Strategies for designing and optimizing new generation vaccines.

Although the field of immunology developed in part from the early vaccine studies of Edward Jenner, Louis Pasteur and others, vaccine development had largely become the province of virologists and other microbiologists, because the model for classic vaccines was to isolate the pathogen and prepare a killed or attenuated pathogen vaccine. Only recently has vaccinology returned to the realm of immunology, because a new understanding of immune mechanisms has allowed translation of basic discoveries into vaccine strategies.

Mucosal AIDS vaccine reduces disease and viral load in gut reservoir and blood after mucosal infection of macaques.

Given the mucosal transmission of HIV-1, we compared whether a mucosal vaccine could induce mucosal cytotoxic T lymphocytes (CTLs) and protect rhesus macaques against mucosal infection with simian/human immunodeficiency virus (SHIV) more effectively than the same vaccine given subcutaneously. Here we show that mucosal CTLs specific for simian immunodeficiency virus can be induced by intrarectal immunization of macaques with a synthetic-peptide vaccine incorporating the LT(R192G) adjuvant. This response correlated with the level of T-helper response. After intrarectal challenge with pathogenic SHIV-Ku2, viral titers were eliminated more completely (to undetectable levels) both in blood and intestine, a major reservoir for virus replication, in intrarectally immunized animals than in subcutaneously immunized or control macaques. Moreover, CD4+ T cells were better preserved. Thus, induction of CTLs in the intestinal mucosa, a key site of virus replication, with a mucosal AIDS vaccine ameliorates infection by SHIV in non-human primates.

Genetic control of immune response to myoglobin. Ir gene function in genetic restriction between T and B lymphocytes.

We studied the genetic restrictions on the interaction between T cells, B cells, and antigen-presenting cells (APC) involved in the H-2-linked Ir gene control of the in vitro secondary antibody response to sperm whale myoglobin (Mb) in mice. The B cells in this study were specific for Mb itself, rather than for a hapten unrelated to the Ir gene control, as in many previous studies. Low responder mice immunized in vivo with Mb bound to an immunogenic carrier, fowl gamma globulin (F gamma G), produced B cells competent to secrete anti-Mb antibodies in vitro if they received F gamma G-specific T cell help. However, (high-responder X low responder) F1 T cells from Mb-immune mice did not help these primed low responder (H-2k or H-2b) B cells in vitro, even in the presence of various numbers of F1 APC that were demonstrated to be component to reconstitute the response of spleen cells depleted by APC. Similar results were obtained with B6 leads to B6D2F1 radiation bone marrow chimeras. Genotypic low responder (H-2b) T cells from these mice helped Mb-primed B6D2F1B cells plus APC, but did not help syngeneic chimeric H-2b B cells, even in the presence of F1 APC. In contrast, we could not detect any Ir restriction on APC function during these in vitro secondary responses. Moreover, in the preceding paper, we found that low responder mice neonatally tolerized to higher responder H-2 had competent Mb-specific helper T cells capable of helping high responder but not low responder B cells and APC. Therefore, although function Mb-specific T cells and B cells both exist in low responder mice, the Ir gene defect is a manifestation of the failure of syngeneic collaboration between these two cell types. This genetic restriction on the interaction between T cells and B cells is consistent with the additional new finding that Lyb-5-negative B cells are a major participant in ths vitro secondary response because it is this Lyb-5-negative subpopulation of B cells that have recently been shown to require genetically restricted help. The Ir gene defect behaves operationally as a failure of low responder B cells to receive help from any source of Mb-specific T cells either high responder, low responder, or F1. The possible additional role of T cell-APC interactions, either during primary immunization in vivo or in the secondary culture is discussed.

Genetic control of the immune response to myoglobins. Both low and high responder T cells tolerant to the other major histocompatibility complex help high but not low responder B cells.

We sought to examine the role of immune response (Ir) genes in helper T cells. To eliminate allogeneic effects, we used neonatally tolerized mice. The results bear not only on the mechanism of Ir genes, but also on the development of the T cell repertoire. B 10.BR (H-2(k)) or C57BL/10 (H-2(b)) mice, which were low responders to myoglobin (Mb), were neonatally tolerized to high responder H-2(d) alloantigens, and B10.D2 mice, which were high responders to Mb, were neonatally tolerized to low responder H-2(k) or H-2(b) alloantigens. Spleen cells from these tolerized mice did not show any reactivity in mixed-lymphocyte reaction or cell-mediated lympholysis against alloantigens used in tolerization. Mb-immune F(1) B cells were helped comparably by Mb-immune tolerized low or high responder T cells. Thus, low responder T cells functioned equivalently to high responder T cells. The failure of nonimmune T cells from tolerized low responder mice to help F(1) B cells and antigen-presenting cells (APC) indicated that collaboration between B10.BR or C57BL/10 T cells and F(1) B cells was not caused by a positive allogeneic effect. Spleen cells from tolerized mice were contaminated with 2-4 percent chimeric F(1) cells, as judged by fluorescence-activated cell sorter analysis, and no F(1) alloantigens were detectable in the thymus. However, removal of chimeric F(1) T cells from the tolerized cell population by treatment with anti-H-2 and complement did not change the helper activity of tolerized low responder T cells. These data indicated that helper activity in the T cell population from low responder mice was not due to F(1) cells. Also, the level of contamination was not sufficient to quantitatively account for the help. In examining the genetic restriction of these tolerized T cells, we found that T cells from tolerized low responder B10.BR or C57BL/10 mice helped F(1) or high responder B10.D2 B cells and APC but not syngeneic B10.BR or C57BL/10 B cells and APC, which were immunized with Mb-coupled fowl gamma globulin instead of Mb to prime low responder B cells with Mb. On the other hand, high responder B 10.D2 tolerized T cells helped syngeneic B 10.D2 B cells but not allogeneic low responder B10.BR B cells. These data indicated that clones of helper T cells specific for Mb exist in low responder mice, and these are not phenotypically different from those in high responder mice, in that both help high responder and F(1) but not low responder B cells and APC. These data are discussed in terms of the mechanism for Ir gene control, and the mechanism of T cell repertoire development- whether intra- or extrathymically-in neonatally tolerized mice.

Immunization with antigen and interleukin 2 in vivo overcomes Ir gene low responsiveness.

We studied the effect of purified interleukin 2 (IL-2), made by recombinant DNA techniques, on the serum antibody response to myoglobin in high- and low-responder mice. Previous studies (6, 7) have shown that this response is controlled by H-2-linked Ir genes. The IL-2 was emulsified with the antigen in complete Freund's adjuvant to provide a sustained high local concentration. In low-responder B10.BR mice, a single dose (optimum 50,000 U) resulted in a consistent 10-50-fold increase in specific serum antibody throughout the time course of the response, from 10 d to 46 d after immunization. In contrast, no effect of IL-2 was seen in congenic high-responder B10.D2 mice. With IL-2, the low-responder mice achieved specific antibody levels comparable to those of high responders. Vehicle alone had no effect, and IL-2 alone, without antigen, did not induce myoglobin-specific antibody. No effect of IL-2 was seen in athymic nude mice of high-responder H-2 haplotype. The effect of IL-2 may be on a small number of responding T cells in the low responder mice, but it is possible that IL-2 also acts directly on B cells in a response that remains T-dependent, and therefore is not observed in athymic mice. We suggest that IL-2 may enhance suboptimal T cell help in the low responder, whereas help is not limiting in the high responder. This approach may enable the study of antibody responses in low responders otherwise too weak to analyze, and may be useful in producing antibodies to poorly immunogenic antigens. Potential clinical uses include immunization with weak antigens in normal patients, or with any antigen in certain immunodeficient patients.

T cell clones specific for an amphipathic alpha-helical region of sperm whale myoglobin show differing fine specificities for synthetic peptides. A multiview/single structure interpretation of immunodominance.

The T cell response to sperm whale myoglobin in the H-2d haplotype has been shown to be largely focused on a limited region around glutamic acid 109 recognized in association with I-Ad. T cell clones 9.27 and 1.2 have been previously (4, 5) shown to reflect this specificity and MHC restriction. In this study we have used a panel of synthetic peptides from the region 102-118 of myoglobin to characterize the specificities of these representative clones. The segment from 106-118 was found to represent a consensus region for recognition by both clones. However, we saw significant differences between clones in the hierarchy of responsiveness to peptides within the panel. In as much as the peptide and the I-Ad molecule remain constant, these differences derive from differences in how each T cell receptor interacts with the antigen. This peptide segment is an amphipathic alpha helix in native myoglobin, meaning that one side is hydrophobic and the other hydrophilic. It is one of the prototype cases that led us to find that amphipathic helices constitute the majority of immunodominant sites recognized by helper T cells (1). It is likely that the peptide will refold into an amphipathic helix stabilized by the interface at the surface of the presenting cell. When such secondary conformation is considered, these data are consistent with a model of multiple T cell specificities arising from multiple views of a single antigen conformation at a single Ia-binding site and do not require postulation of multiple conformations or binding sites. Additionally, the finding of distinct specificities suggests that the immunodominance of this site depends not on the dominance of a single clone, but on the focusing of a polyclonal response on a single region of the molecule in association with I-Ad. The immunodominance of this particular region of the protein may thus depend on intrinsic features of the site, such as potential to form an amphipathic helix, as well as extrinsic factors such as binding properties of the I-A molecule.

An immunodominant class I-restricted cytotoxic T lymphocyte determinant of human immunodeficiency virus type 1 induces CD4 class II-restricted help for itself.

We have observed that a peptide corresponding to an immunodominant epitope of the HIV-1 envelope protein recognized by class I MHC-restricted CD8+ CTL can also induce T cell help for itself. The help is necessary for restimulation of CTL precursors in vitro with peptide alone in the absence of exogenous lymphokines, can be removed by depletion of CD4+ T cells, and can be replaced by exogenous IL-2. Whereas the CTL in BALB/c or B10. D2 mice are restricted by the class I molecule Dd, the Th cells are restricted by the class II molecule Ad, and the help can be blocked by anti-Ad mAb. To examine the genetic regulation of the induction of help, we studied B10.A mice that share the class I Dd molecule, but have different class II molecules, Ak and Ek. Spleen cells of immune B10.A mice behave like CD4-depleted BALB/c spleen cells in that they cannot be restimulated in vitro by the peptide alone, but can with peptide plus IL-2. Therefore, in the absence of exogenous lymphokines, peptide-specific help is necessary for restimulation with this immunodominant CTL epitope peptide, and in H-2d mice, this peptide stimulates help for itself as well as CTL. We speculate on the implications of these findings for the immunodominance of this peptide in H-2d mice, and for the selective advantage of pairing certain class I and class II molecules in an MHC haplotype.

Influences of antigen processing on the expression of the T cell repertoire. Evidence for MHC-specific hindering structures on the products of processing.

Two lines of evidence in the current study indicate that antigen processing is a major factor, in addition to MHC binding and T cell repertoire, that determines Ir gene responsiveness and epitope immunodominance. First, immunization with synthetic peptides of myoglobin sequences revealed new reactivities that had not appeared after priming with native myoglobin. For example, B10.S mice (H-2S) immune to equine myoglobin predominantly responded to peptide 102-118, whereas there was little, if any, response to this peptide in B10.BR (H-2k) mice immunized with native equine myoglobin. However, after immunization with the 102-118 peptide, both strains responded to the peptide. After in vitro restimulation, B10.BR T cells responded as well as B10.S T cells. Similarly, some individual 102-118-specific T cell clones from mice of both haplotypes showed similar dose responses and fine specificity patterns. Thus, low responsiveness to this site is due neither to a hole in the repertoire nor to a failure to bind to the appropriate MHC molecule. An alternative explanation was suggested by the observation that, whereas B10.S T cells from peptide 102-118-immune mice responded almost as well to whole myoglobin as to the peptide, the B10.BR T cells from peptide immune mice, while responding well to peptide, were poorly stimulated by whole myoglobin. Thus, the product of natural processing of equine myoglobin probably has hindering structures in the regions flanking the core epitope 102-118 that interfere with presentation by I-Ak but not I-AS. The second line of evidence that processing of native myoglobin may influence the apparent specificity of the T cell response was obtained using the I-Ad-restricted sperm whale myoglobin 102-118-specific clone 9.27. This clone discriminated readily between whole sperm whale myoglobin and equine myoglobin, but it did not distinguish between peptides corresponding to 102-118 of the sperm whale and equine sequences. This distinction between equine peptide and native equine myoglobin could be overcome by artificial "processing" of equine myoglobin with cyanogen bromide. In both sets of experiments, F1 APCs that present the same epitope well to T cells of another haplotype failed to overcome the defect, which was therefore not due to the availability of different processed cleavage fragments in APC of different haplotypes, as would be expected if there were MHC-linked processing. Thus, the differential responses to peptides versus native molecule for both I-Ad- and I-Ak-restricted clones appeared to depend on the restricting molecule used.(ABSTRACT TRUNCATED AT 400 WORDS)

Limiting dilution comparison of the repertoires of high and low responder MHC-restricted T cells.

To approach the mechanism that determines Ir gene-controlled high or low responsiveness to whole proteins, such as sperm whale myoglobin (SWMb), we compared the repertoires of high and low responder haplotype-restricted T cells for different myoglobin epitopes by limiting dilution frequency analysis. Poisson analysis was performed using long-term limiting dilution cell lines of (B10.BR [low] X B10.D2[high])F1 T cells maintained on high or low responder APCs. The cell lines were tested with SWMb peptides and fragments for T cell repertoire fine specificities and Ia restrictions. The frequency of SWMb-specific F1 T cells responsive on B10.BR (H-2k) APCs was 2.5-3.6-fold lower than on B10.D2 (H-2d) APCs. Strikingly, all of the H-2k-restricted T cells used I-Ek as a restriction element, whereas both I-Ad- and I-Ed-restricted T cells were found among the H-2d-restricted lines. The I-Ad-restricted T cells were dominant, and the majority was specific for the synthetic peptide 102-118. T cells specific for peptide 132-146, dominant in association with I-Ed, were less frequent. However, no detectable H-2k-restricted T cells were specific for either of these peptides, but instead they were specific for fragment 1-55 or peptide 59-80. Fragment 1-55 also stimulated a similar number of H-2d-restricted T cells. Therefore, the low response of F1 T cells on H-2k-presenting cells may be due to the failure to see myoglobin plus I-Ak, in particular the immunodominant site around Glu 109, in contrast to the dominant response of high responder mice (both H-2d and H-2s) focused on the I-A molecule and the site around residue Glu 109. The I-E- low responder B10 strain also failed to respond to peptide 102-118, supporting the idea that the low responder status results from a limited repertoire lacking response to 102-118 plus I-A. In those strains that respond to the immunodominant site 102-118, the frequency of T cells in the repertoire specific for this site was always considerably greater than that for other sites. These results suggest that there is an important difference between immunodominant epitopes and minor epitopes and that Ir gene-controlled low responsiveness to a natural whole protein may be due primarily to the failure to respond to a single immunodominant site, even though a number of other epitopes can be recognized.

Genetic control of the immune response to staphylococcal nuclease. VII. Role of non-H2-linked genes in the control of the anti-nuclease antibody response.

The role of non-H-2-linked genes in the control of the antibody response to staphylococcal nuclease has been investigated. 3 wk after immunization with nuclease in complete Freund's adjuvant, strain A/J (H-2 a) mice produced significantly higher titers of antibody than strain B10.A (H-2(a)) mice, whereas mice of strains A.BY (H-2(b)) and B10 (H-2(b)) produced barely detectable titers. With hyperimmunization, A/J and A.BY mice reached the same peak levels for antibody titers, both severalfold higher than those reached by B10.A and B10 mice. Analysis of the specificity of antibodies by assessment of binding to two fragments of nuclease showed similarities between strains of the same H-2 haplotype. These results suggest that although H-2-1inked genes determined initial responsiveness at 3 wk and the relative proportions of antibodies directed toward different antigenic determinants on the nuclease molecule, non-H-2-linked genes determined the overall magnitude of the hyperimmuneresponse. Measurement of the affinity of the antibodies to the nuclease fragment (1-126) showed that strains B10 and B10.A produced antibodies with 7- to 10-fold higher affinity than comparable antibodies from strains A.BY and A/J. In a backcross of (B10.A x A/J) x B10.A, the level of antibody segregated independently of the Ig-1(e) C(H) allotype and the A/J anti-nuclease idiotypes. Thus, a gene(s) linked to neither H-2 nor heavy chain structural genes appears to control the aggregate response to antigenic determinants on the nuclease molecule independent of subspecificities of these antibodies or their idiotype.

Immunologically relevant peptide antigen exists on the presenting cell in a manner accessible to macromolecules in solution.

Although studies of the association of antigen with APC have been complicated by antigen-processing requirements, recent studies have suggested that immunologically relevant antigen should be present on the APC surface. Nevertheless, blocking of antigen presentation with antibody to the antigen has not been demonstrable in most systems. To study this problem we developed a system using avidin to block presentation of amino-terminal biotinylated synthetic peptide 132-146 of sperm whale myoglobin (B132) to a murine T cell clone specific for this site in association with I-Ed. greater than 95% specific inhibition was observed with doses of B132 equipotent to unmodified peptide. Specific blocking could be observed: (a) after pulsing APC with antigen, washing, and incubating for a chase period of 8-16 h before addition of avidin and T cells to assure adequate time for intracellular trafficking and maximal display of antigen on the cell surface, or (b) when monensin is present during the antigen pulse to inhibit such traffic. Therefore, the inhibition appeared to be occurring at the cell surface unless dissociation and reassociation were constantly occurring. To distinguish these, B10.GD APC (I-Ed-negative) were pulsed with antigen and cocultured with B10.D2 APC (I-Ed-positive). No detectable antigen presentation resulted. Thus, minimal dissociation and reassociation between antigen and APC occurs and, consequently, blocking by extracellular solution-phase binding of avidin to antigen is unlikely. Taken together, these data suggest that the blocking is occurring at the cell surface. Thus, under physiologic conditions, immunologically relevant antigen necessary for T cell activation appears to be present on the APC surface and is freely accessible to macromolecules the size of avidin. These findings hold specific implications for models of antigen presentation for T cell recognition.

A major anti-myoglobin idiotype. Influence of H-2-linked Ir genes on idiotype expression.

A rabbit antiidiotypic antiserum raised against an A.SW IgG1K monoclonal anti-sperm whale myoglobin (Mb) antibody, HAL19, and extensively absorbed with normal mouse immunoglobulin and MOPC 21 (IgG1K), was found to detect a common or major anti-Mb idiotype expressed by some but not all anti-Mb monoclonal antibodies, regardless of immunoglobulin G (IgG) subclass, and by 40-50% of the anti-Mb antibodies in immune serum from five high responder strains of mice representing five different Igh allotypes. It did not inhibit antibodies to three unrelated protein antigens. The fraction of antibodies expressing this idiotype, denoted IdHAL19, was regulated by H-2-linked genes that correlated exactly in four independent haplotypes and an F1 with the known Mb immune response (Ir) genes and may be identical to these. Whereas less than 50% of antibodies from high responder mice were inhibitable by anti-IdHAL19, greater than 80% of antibodies from low responder mice, tested at comparable final antibody concentration, were inhibitable. This result was true for both low responder haplotypes, H-2b (B10) and H-2k (B10.BR). The idiotype was found to be present on antibodies that bound to native Mb but not fragments 1-55 or 132-153 of Mb or a denatured form, S-methyl Mb. This specificity for native Mb paralleled that of the monoclonal idiotype HAL19 itself. Therefore, the production of antibodies specific for native in contrast to denatured Mb was studied in H-2-congenic high and low responder strains. Strikingly, low responders produced antibodies that reacted almost exclusively with the native conformation, whereas a larger proportion of antibodies from high responder mice also reacted with the denatured form, S-methyl Mb. Bypassing of the Ir gene defect by immunization with Mb attached to a carrier, F gamma G, resulted in low responder antisera resembling higher responder sera in both idiotype expression and conformational specificity. The simplest explanation of these results is that H-2-linked Ir genes control antibody fine specificity, which is reflected in the idiotypes of the variable regions expressed. We suggest that low responder mice produce a more limited repertoire of antibodies consisting primarily of IdHAL19-positive antibodies specific for the native conformation of Mb. High responder mice produce a greater diversity of antibodies to Mb, so that the IdHAL19-positive, conformation-specific population represents a smaller proportion of the total. Similarly, the use of carrier-specific helper T cells in low responder mice results in a greater diversity of antibodies, which dilutes out the IdHAL19 subset.(ABSTRACT TRUNCATED AT 400 WORDS)

Genetic control of the immune response to staphylococcal nuclease. IV. H-2-linked control of the relative proportions of antibodies produced to different determinants of native nuclease.

The relative proportions of antibodies of different specificities within antisera raised to native staphylococcal nuclease have been studied in several strains of mice in which the antibody response has been shown to be under H-2-linked Ir-gene control. A method was developed in which binding to different radiolabeled fragments of nuclease was titrated against increasing fragment concentration until the binding capacity of the antiserum for that fragment was saturated. In comparing the low responder (H-2b) strain C57BL/10 with its congenic high responder counterpart B10.A (H-2a), it was found that the two strains made markedly and reproducibly different proportions of antibodies to different determinants on native nuclease. Since these two strains differ only at H-2, and therefore have identical immunoglobulin structural gene repertoires, we conclude that H-2-linked Ir genes can control the response to different determinants on the same antigen molecule independently of one another. This result suggests a possible role of H-2-linked genes in the selection of specific B cells.

Cytokine interactions in human immunodeficiency virus-infected individuals: roles of interleukin (IL)-2, IL-12, and IL-15.

Cytokines have been shown to be powerful regulators of the immune response. In this study, we analyze the effect that the newly recognized cytokine interleukin (IL)-15 has on proliferation and cytokine induction using peripheral blood mononuclear cells (PBMCs) and purified CD4+ T cells from patients infected with human immunodeficiency virus (HIV) who are at various stages in their disease. We observed that IL-15 enhances the proliferative response in a dose-dependent manner from PBMCs of HIV-infected individuals when stimulated by polyclonal mitogen, tetanus toxoid, or HIV-specific antigen. The effects of exogenous IL-15 are substantially diminished by adding a neutralizing antibody to the beta chain of the IL-2 receptor. Moreover, the ability of IL-15 to increase proliferation is enhanced by the presence of endogenous IL-2 produced in the cultures. The effect that exogenous IL-15 had on IL-2, IL-4, and interferon (IFN)-gamma induction from PBMC's or CD4+ T cells in response to mitogen or tetanus toxoid was also examined. This was compared to the effect that exogenous IL-2 and IL-12 had under the same conditions. Addition of IL-2 or IL-15 to short-term in vitro cultures of either PBMCs or CD4+ T cells had little effect on IL-2, IL-4, or IFN-gamma production. By contrast, IL-12 caused substantial enhancement of both IL-2 and IFN-gamma production from these cultures. The role that endogenous cytokines have on IFN-gamma induction was also studied. Addition of a neutralizing antibody to the alpha chain of the IL-2 receptor or IL-12 to antigen stimulated cultures caused a striking decrease in IFN-gamma production. Neutralization of endogenous IL-15 also resulted in diminished IFN-gamma production from cultures stimulated with mitogen. IL-4 and IFN-gamma protein production by PBMCs and CD4+ T cells stimulated with mitogen was assessed to see if we could detect a specific bias of cytokine production. Small amounts of IL-4 were detected from CD4+ T cells but not PBMCs from most individuals tested. IFN-gamma and IL-2, however, were also produced from these same cultures. These results further elucidate the mechanism of cytokine regulation in HIV-infected individuals, and they provide evidence that IL-15 may be a useful immune modulator.

Supraoptimal peptide-major histocompatibility complex causes a decrease in bc1-2 levels and allows tumor necrosis factor alpha receptor II-mediated apoptosis of cytotoxic T lymphocytes.

Cytotoxic T lymphocytes (CTLs) are primary mediators of viral clearance, but high viral burden can result in deletion of antigen-specific CTLs. We previously reported a potential mechanism for this deletion: tumor necrosis factor (TNF)-alpha-mediated apoptosis resulting from stimulation with supraoptimal peptide-major histocompatibility complex. Here, we show that although death is mediated by TNF-alpha and its receptor (TNF-RII), surprisingly neither the antigen dose dependence of TNF-alpha production nor that of TNF-RII expression can account for the dose dependence of apoptosis. Rather, a previously unrecognized effect of supraoptimal antigen in markedly decreasing levels of the antiapoptotic protein Bc1-2 was discovered and is likely to account for the gain in susceptibility or competence to sustain the death signal through TNF-RII. This decrease requires a signal through the TCR, not just through TNF-RII. Although death mediated by TNF-RII is not as widely studied as that mediated by TNF-RI, we show here that it is also dependent on proteolytic cleavage by caspases and triggered by a brief initial encounter with antigen. These results suggest that determinant density can regulate the immune response by altering the sensitivity of CTLs to the apoptotic effects of TNF-alpha by decreasing Bc1-2 levels.

Role of antigen, CD8, and cytotoxic T lymphocyte (CTL) avidity in high dose antigen induction of apoptosis of effector CTL.

Experimental data suggest that negative selection of thymocytes can occur as a result of supraoptimal antigenic stimulation. It is unknown, however, whether such mechanisms are at work in mature CD8+ T lymphocytes. Here, we show that CD8+ effector cytotoxic T lymphocytes (CTL) are susceptible to proliferative inhibition by high dose peptide antigen, leading to apoptotic death mediated by TNF-alpha release. Such inhibition is not reflected in the cytolytic potential of the CTL, since concentrations of antigen that are inhibitory for proliferation promote efficient lysis of target cells. Thus, although CTL have committed to the apoptotic pathway, the kinetics of this process are such that CTL function can occur before death of the CTL. The concentration of antigen required for inhibition is a function of the CTL avidity, in that concentrations of antigen capable of completely inhibiting high avidity CTL maximally stimulate low avidity CTL. Importantly, the inhibition can be detected in both activated and resting CTL. Blocking studies demonstrate that the CD8 molecule contributes significantly to the inhibitory signal as the addition of anti-CD8 antibody restores the proliferative response. Thus, our data support the model that mature CD8+ CTL can accommodate an activation signal of restricted intensity, which, if surpassed, results in deletion of that cell.

Genetic control of the immune response to staphylococcal nuclease. III. Time-course and correlation between the response to native nuclease and the response to its polypeptide fragments.

The progression of the Ir gene-controlled antibody response to staphylococcal nuclease in mice with repeated immunizations has been examined. H-2-linked control of the response to a single immunization with 100 mug of nuclease in complete Freund's adjuvant was confirmed. However, among strains of the high responder H-2a haplotype, the response of the A/J mice was about 10-fold higher than that of the B10.A, indicating additional non-H-2-linked control. In addition, the low responder C57BL/10 (H-2b) strain produced antibody levels as high as or higher than those of the congenic high responder B10.A (H-2a) strain when both strains were repeatedly immunized, indicating complexity even in the H-2-linked control of the response to this small monomeric protein. Polypeptide fragments of nuclease were also studied as immunogens. The antibody response to one fragment (residues 99-149) was found to follow the same pattern among five strains tested as that to whole nuclease. However, in this case the C57BL/10 was found to be a nonresponder rather than a low responder, failing to develop a response despite repeated immunizations. In contrast, the C57BL/10 showed a low but significant response to another fragment (residues 1-126) of nuclease. These results suggest that the apparent H-2-linked control of the response to whole nuclease is a reflection of the ability to recognize a determinant(s) in the region from residues 99 to 149, and that the eventual response of the C57BL/10 strain after hyperimmunization reflects the recognition of other determinants. If these observations reflect the common recognition of a determinant on native nuclease and on a random-conformation fragment, they have implications about the conformational specificity of the receptors, or the flexibility of the determinants, involved in H-2-linked Ir-gene control. In addition, evidence is presented for a possible second H-2-linked gene (or genes) controlling the response to other determinants of nuclease expressed on the polypeptide fragments.

Interleukin 2 receptor expression in unstimulated murine splenic T cells. Localization to L3T4+ cells and regulation by non-H-2-linked genes.

The present study reports the surprising observation that IL-2-R+ cells can be detected in fresh, unstimulated, murine spleen T cells from unimmunized mice by flow cytometry using the monoclonal anti-receptor antibody 7D4. Also, unexpectedly, these cells were found exclusively in the L3T4+Lyt-2- population by two-color fluorescence, in contrast to receptor+ cells after stimulation, in which both L3T4+Lyt-2- and Lyt-2+L3T4- cells were found. The fraction of splenic T cells bearing IL-2-R reproducibly varies twofold under non-H-2-linked genetic control, with high expression in DBA/2 and BALB/c (approximately 6-7%) and low expression in B10.D2 and C57BL/6 (3%). This correlates quantitatively with a greater responsiveness of the DBA/2 and BALB/c splenic T cells to high doses of IL-2, compared with B10.D2 T cells; twice as many B10.D2 T cells as DBA/2 T cells were required to get the same response. Studies with 23 B X D RI strains revealed that the level of IL-2-R+ cells in unstimulated spleen cells was regulated by multiple genes, very likely including at least one gene on chromosome 7, near the HBB locus. The mapping makes novel use of nonparametric (Smirnov) statistics, which we suggest may be of general usefulness in similar analyses of RI strains.

Genetic control of the immune response in mice to a Plasmodium falciparum sporozoite vaccine. Widespread nonresponsiveness to single malaria T epitope in highly repetitive vaccine.

Different H-2 congenic strains of mice were immunized with a P. falciparum sporozoite vaccine currently being tested in humans, or with different segments of the vaccine molecule. Specific IgG production or lymph node cell proliferation in response to different antigens was then determined. Only four of seven strains (representing three of eight possible different class II restriction molecules) responded to the vaccine. Of those restriction molecules, only one, I-Ab, was associated with a response to a malaria-encoded T epitope [contained within NP(NANP)3NA], while the other two molecules (E alpha dE beta d and E alpha kE beta s) were associated with a T cell response to a nonmalarial epitope(s) carboxyterminal to the malaria sequence and encoded by a tetracycline resistance gene, read out of frame. If an analogous situation applies in humans, natural boosting by sporozoites will be very restricted. This has serious implications for the effectiveness of the vaccine, since constant high levels of antisporozoite antibodies and possibly antibody-independent T cell effector functions are required for immunity.

Serum angiotensin-1 converting enzyme activity processes a human immunodeficiency virus 1 gp160 peptide for presentation by major histocompatibility complex class I molecules.

T cell stimulation by the human immunodeficiency virus 1 gp160-derived peptide p18 presented by H-2Dd class I major histocompatibility complex molecules in a cell-free system was found to require proteolytic cleavage. This extracellular processing was mediated by peptidases present in fetal calf serum. In vitro processing of p18 resulted in a distinct reverse phase high performance liquid chromatography profile, from which a biologically active product was isolated and sequenced. This peptide processing can be specifically blocked by the angiotensin-1 converting enzyme (ACE) inhibitor captopril, and can occur by exposing p18 to purified ACE. The ability of naturally occurring extracellular proteases to convert inactive peptides to T cell antigens has important implications for understanding cytotoxic T lymphocyte responses in vivo, and for rational peptide vaccine design.