Roadmap on digital holography [Invited].

This Roadmap article on digital holography provides an overview of a vast array of research activities in the field of digital holography. The paper consists of a series of 25 sections from the prominent experts in digital holography presenting various aspects of the field on sensing, 3D imaging and displays, virtual and augmented reality, microscopy, cell identification, tomography, label-free live cell imaging, and other applications. Each section represents the vision of its author to describe the significant progress, potential impact, important developments, and challenging issues in the field of digital holography.

Purification of functional, determinant-specific, idiotype-bearing murine T cells.

Strain A/J mice immunized with azobenzenearsonate (ABA)-mouse IgG conjugates develop suppression for anti-trinitrophenyl(TNP) responses to doubly conjugated (ABA,TNP) proteins. This suppression is specific for the ABA epitope and is mediated by T cells in cell transfer experiments. ABA-binding T cells from suppressed animals were purified by a two-stage procedure in which B cells were removed from spleen cell populations by adherence to plastic surfaces coated with anti-mouse Ig antibody, followed by binding the nonadherent population (more 95 percent Thy-1-positive) to surfaces coated with ABA-protein conjugates. Approximately 90 percent of the cells recovered by temperature-dependent elution from the ABA plates (similar to 2 percent of the spleen cells) bound antigen immediately afterward, and up to 50 percent of the cells bound anti-cross-reactive idiotype antibody. On the other hand, the nonadherent T-cell population was completely negative in the antigen- binding and idiotype assays. Another distinguishing feature of the two T-cell populations was that 78 percent of the adherent cells, but only 2 percent of the nonadherent cells, were Ia positive, although the specific I-region marker(s) expressed on the cells was not identified. The biological function of the antigen-binding T cells was investigated using a standard cell transfer protocol. Suppressor cells were enriched in the adherent population by a factor of at least 25, establishing that functional, epitope-specific, idiotype-bearing T cells can be significantly purified by this procedure. Note Added in Proof. We have recently isolated two types of ABA-binding molecules biosynthetically labeled with (35)S-methionine from NP-40 lysates of purified antigen-specific T cells. The molecules were purified by adsorption onto an ABA-Sepharose immunoadsorbent followed by elution with 9 M urea. Autoradiograms of SDS-PAGE of the eluates revealed components with tool wt of approximately 60,000 and 33,000 dahons. These molecules were not present in eluates from a bovine IgG-Sepharose control immunoadsorbent and thus represent specific ABA-binding products synthesized by T cells.

A hemolytic plaque assay for activated murine T cells.

In an earlier report, it was shown that murine spleen cells cultured with concanavalin A (Con A) released into the culture supernatants helper and suppressor substances for antibody production. The present communication describes the production of rabbit antisera against culture supernates from Con A-activated spleen cells and their use in a plaque assay for mitogen-activated T cells. The plaque assay, utilizing SRBC to which Staphylococcal protein A had been coupled, the developing anti-supernatant antiserum and guinea pig complement, readily detected secreting T cells. The T-cell nature of the plaque-forming cells (PFC) was established principally by the following: (a) the majority of lymphocytes in the centers of plaques were Thy-1-positive by fluroescence; (b) spleen cells depleted of B cells by incubation in plastic dishes coated with rabbit anti-mouse Ig antibody gave greatly enriched PFC responses; (c) anti-Thy-1 and anti-Lyt-2.2 treatment of spleen cells almost completely depleted PFC; (d) T-cell mitogens (Con A and phytohemagglutinin) but not B-cell mitogens (lipopolysaccharides) induced PFC responses; (e) T cells maintained in culture for 10 d with Con A and T-cell growth factor yielded PFC. Kinetic and dose response studies showed that high doses of mitogen induced rapidly appearing T-PFC and the responses peaked at day 1--2 of culture. Lower doses of mitogen-induced PFC required longer periods of incubation for detection, indicating that cell activation and secretion may be different dose-dependent activities of mitogens. Another noteworthy finding was that the antiserum reacted with surface antigens of T-PFC, indicating that secreted products are expressed on the membranes of T cells, offering the possibility of isolating populations of cells with specific secretory potential. Although the precise nature of the T-cell products detected by the antiserum used in this assay are unresolved, 10% of the target-cell-adherent population from spleen cells of BALB/c mice sensitized to L929 cells formed plaques. This suggests that the antiserum has significant activity against the products of cytotoxic T cells, a finding which accords with the activity of anti-Lyt-2.2 serum against mitogen-induced T-PFC. The method clearly offers new possibilities for the analysis of T cells and their products and should provide an important approach to the clonal analysis of lymphokine production.

The chemical nature of macrophage RNA-antigen complexes and their relevance to immune induction.

10 different compounds, including natural and synthetic polypeptides, proteins, polysaccharides, amino acids, and steroid hormones, were assayed for their capacity to form complexes with peritoneal exudate cell RNA. Only molecules carrying negatively charged groups were able to do so. The formation of RNA-antigen complexes was unrelated to the immuno-potency of the "antigen," was not an enzyme-dependent reaction, did not require the synthesis of RNA following introduction of the antigen, did not seem to involve antigen-specific RNAs, was not specific for macrophages, since HeLa cells could be used as effectively, and occurred when purified RNA was mixed with antigen only in the presence of divalent cations. The complexes were very stable, once formed, but could be dissociated by exhaustive dialysis against buffers containing a chelating agent. The macrophage RNA-antigen complex therefore appears to be a chelate between anionic groups on the two components. Based on the total absence of a relationship between immunogenicity and the capacity to form such complexes, as well as the nonspecific nature of complex formation at every level examined, it appears unlikely that RNA-antigen complexes play a physiologically significant role in immune induction.

Carrier-directed anti-hapten responses by B-cell subsets.

The capacity of the trinitrophenyl (TNP) haptenic group, coupled to a series of chemically dissimilar carriers, to cross-stimulate putative T- dependent and T-independent murine B-cell subpepulations was determined by using an in vitro limiting dilution technique to generate primary IgM responses. It was found that TNP-Ficoll and TNP-dextran, two T- independent antigens with little or no polyclonal mitogenicity, stimulate the same population of anti-TNP precursors, which is distinct from the precursor population activated by TNP-bacterial lipopolysaccharide (LPS), a T-independent polyclonal mitogen, or TNP-horse erythrocytes (HRBC), a T-dependent antigen. On the other hand, TNP-LPS and TNP-HRBC activate the same precursor population, indicating that LPS can substitute for the T- cell signal in T-dependent B-cell responses, whereas nonmitogenic T- independent antigens cannot. However, the cumulative evidence from this and other laboratories strongly indicates that LPS and T-dependent antigens activate B cells by different mechanisms. Of particular interest, LPS is incapable of activating B cells responsive to weakly- or nonmitogenic T-independent antigens. Based on clonal burst size, T-dependent antigens are capable of inducing greater antigen-specific B-cell proliferation than T-independent antigens. However, TNP conjugates of Ficoll and dextran, which are relatively poor inducers of polyclonal B-cell activation, induced larger anti-TNP clones than did TNP-LPS, a strong polyclonal mitogen. The findings reinforce the evidence favoring existence of multiple B- cell subpopulations with distinctive activation pathways. They also strengthen the proposition that a given B-cell subset can be activated by more than one mechanism.

Rosette formation between murine lymphocytes and erythrocytes. A new locus in the H-2 region.

More than 5% of murine splenic lymphocytes form rosettes with syngeneic erythrocytes. This property was maximally expressed when the lymphocytes were cultured for 24 h before rosetting. About 70% of the rosetting lymphocytes were B cells and 30% were T cells on the basis of surface immunoglobulin and the Thy-1-antigen. Capping surface immunoglobulin had no effect on the capacity of lymphocytes to form rosettes, indicating that the receptor in question was not immunoglobulin. The capacity of lymphocytes to form rosettes with erythrocytes from other strains of mice was H-2 restricted. Extensive pairings of congenic and recombinant strains as donors of lymphocytes and erythrocytes showed that none of the known loci within the H-2 region-controlled rosetting. The involvement of regions on chromosome 17, telomeric or centromeric to H-2, was also excluded. The data were only compatible with the conclusion that this form of self-recognition is associated with a new locus (or loci) mapping between H-2G and H-2D.

Spatial requirements between haptenic and carrier determinants for T-dependent antibody responses.

To gauge the proximity between cooperating T and B cells required for effective triggering of antibody production, guinea pigs were immunized with bifunctional antigens in which the haptenic and carrier determinants were separated by rigid spacers of varied dimension. These took the form 2,4-dinitrophenol-(proline)n-L-tyrosine-p-azobenzenearsonate, where n varied from 1 to 40 proline residues. Animals immunized with n = 10 and n = 22 compounds made strong anti-DNP antibody responses, whereas animals immunized with bifunctional compounds containing longer spacers did not make antibody detectable by precipitation. It can be calculated on the basis of very strong physicochemical evidence for the rigidity and axial translation of poly-L-proline chains in solution that the cut-off point for effective interaction between T and B cells lies between 69 and 97 A U.

Idiotype profile of an immune response. I. Contrasts in idiotypic dominance between primary and secondary responses and between IgM and IgG plaque-forming cells.

The primary response of A/J mice to p-azobenzenearsonate-keyhole limpet hemocyanin (ABA-KLH) was investigated. A day-by-day analysis at the plaque- forming cell (PFC) level was performed, with inhibition by anti-cross- reactive idiotype (CRI) serum to determine percentage of CRI(+) PFC. A regular pattern in the dynamics of Id (idiotype) dominance was observed. Just as in the NP-b and NP-a systems (9, 12), the major Id (CRI) is more dominant in primary than in secondary or hyperimmune responses. This trend is more apparent in IgG PFC which are generally 80-95 percent CRI(+) at day 10 in the primary response but only 30-40 percent CRI(+) at day 10 in secondary or hyperimmune responses. A somewhat different pattern is seen with IgM PFC. These may reach a peak of 85 percent CRI(+) in the primary response, but secondary or hyperimmune IgM PFC, which are lower in numbers than IgG PFC, remain high in CRI content at approximately 70 percent. The PFC data on extent of id dominance in secondary or hyperimmune responses is fully compatible with previously reported serological data by others. Analysis of IgG PFC by hapten inhibition indicated that heterogeneity was in the order secondary PFC {greater than} primary PFC {greater than} hybridoma AK-2.2 PFC with H(75)/H(25) values of 22.9, 6.2, and 2.7, respectively; where H(75) and H(25) are the hapten concentrations required to give 75 percent and 25 percent of inhibition of PFC, respectively. Hapten inhibition data also suggested that secondary IgG PFC were 10 times higher in median binding avidity for ABA-L-tyrosine than primary IgG PFC. The kinetic analysis strongly indicated that CRI(+) IgM PFC were preferentially switched to IgG PFC in the primary response. In both studies, the CRI content of the earliest-appearing IgG PFC was significantly higher than that of IgM PFC on that day. For example, in one case IgM PFC were 60 percent CRI + on day 6 whereas IgG PFC were 100 percent CRI(+). The high Id dominance and selective isotype switching may have either a B or a T cell basis.

The functional dissection of an antigen molecule: specificity of humoral and cellular immune responses to glucagon.

Bovine glucagon, a polypeptide of 29 amino acids, was immunogenic in guinea pigs. The immunologic determinants of glucagon were investigated using isolated tryptic peptides of the hormone. Antibodies from virtually all of more than two dozen animals had specificity primarily for the amino-terminal heptadecapeptide (NM) and showed little or no binding with the carboxy-terminal undeca- and dodecapeptides (C). The smallest synthetic peptide of a series initiated at residue 16 which measurably bound antibody comprised residues 5-16 of glucagon. In cellular immune assays, both NM and C elicited delayed cutaneous reactions and inhibited the migration of peritoneal cells from immune animals. However, only intact glucagon and its C fragment stimulated lymphoid cells to synthesize DNA. While glucagon was somewhat more active than C, the addition of NM to C did not enhance its transforming activity. The smallest synthetic carboxy-terminal peptide with discernible transforming activity comprised residues 19-29 of glucagon. In both native and synthetic C peptide preparations, the undecapeptide was generally more active than the dodecapeptide, although cells from different animals gave different response patterns. The difference between the two is the presence of arginine at the amino-terminus of the peptide chain. Thus, the recognition specificity of populations of antigen-reactive cells from different animals displays a variation which is at least superficially analogous to that of populations of antibody molecules. In limited experiments using NM and C peptides as immunogens, neither gave rise to delayed hypersensitivity or to glucagon-binding circulating antibody, following a regimen which invariably provoked these responses when glucagon itself served as the immunogen. These results indicate that glucagon was cleaved by trypsin along functional lines into two parts, one of which housed the major antigenic determinant and the other of which carried the major immunogenic determinant, and they are highly compatible with a two-cell mechanism of immune induction. An apparent dissociation between the capacity to provoke delayed hypersensitivity reactions and to transform antigen-reactive cells in culture was observed.

Antigen structural requirements for immunoglobulin isotype switching in mice.

L-Tyrosine-p-azobenzene-p-arsonate (RAT) is immunogenic and serves as a carrier for anti-hapten antibody responses in guinea pigs, rats, and mice. However, the murine anti-N-2,4-dinitrophenyl (DNP) plaque-forming cell (PFC) response to the bifunctional antigen 2,4-dinitrophenyl-6-amino-caproyl-L- tyrosine-p-azobenzene-p-arsonate (DNP-SAC-RAT; or BI-1) is extremely weak (2,000-4,000 PFC/spleen) and exclusively IgM in both primary and secondary responses. The 6-amino-caproyl group serves as a spacer in this antigen between the DNP haptenic and RAT carrier epitopes. In view of recent evidence indicating that different T helper cells synergize for optimal antibody responses, a trifunctional antigen, N-2,4- dinitrophenyl-6-amino-caproyl-L-tyrosine-p-azobenze-p-arsonate-(proline)9-L- tyrosine-p-azobenzene-p-arsonate (DNP-SAC-RAT-PRO(9)-RAT; or TRI), was prepared to investigate the effect of adding a second RAT epitope to BI-1. The nonaproline spacer between the two RAT epitopes in TRI is assumed to be a rigid rod of approximately 28 A. TRI induced about twice as many PFC as BI-1 in primary responses of A/J mice, and induced both IgM and IgG PFC in secondary responses. Furthermore, TRI induced IgG PFC responses in mice primed with p-azobenzene-p-arsonate-keyhole limpet hemocyanin, BI-1, or RAT, whereas boosting with BI-1 failed to induce IgG PFC, even in mice primed with TRI. These findings indicate that the minimum antigen structural requirements for inducing IgG PFC in mice are two carrier epitopes and one haptenic epitope. In addition, priming with a mono-epitope carrier (RAT) is sufficient preparation for IgG responses to a trifunctional immunogen. Because TRI differs from BI-1 by the (proline)(9) spacer as well as the additional RAT epitope, two other compounds, N-2,4-dinitrophenyl-6-amino- caproyl-(proline)(9)-L-tyrosine-p-azobenzene-p-arsonate (DNP-SAC-PRO(9)-RAT; or BI-2) and N-2,4-dinitrophenyl-6-amino-caproyl-(proline)(9)-L-tyrosine-p- azobenzene-arsonate (DNP-SAC-RAT-PRO(10); or BI-3), were prepared to evaluate the possible role of the spacer in the observed responses. BI-2, but not BI-3, induced IgG as well as IgM PFC in TRI-primed mice. However, BI-2 failed to induce IgG responses in RAT-primed mice, indicating that TRI and BI-2 were not equivalent immunogens. Because anti-prolyl antibodies had been found in guinea pigs immunized with N-2,4-dinitrophenyl-(proline)10-L-tyrosine-p- azobenzene-p-arsonate (DNP-PRO(10)-RAT), it seemed possible that priming with TRI might induce anti-prolyl antibodies, which, in turn, could cross-link BI-2 molecules into aggregates containing at least two carrier epitopes. To help resolve this question, mice were immunized with acetyl-(proline)10-L- tyrosine-p-azobenzene-p-arsonate and boosted with BI-2. IgG PFC responses were detected, suggesting that anti-prolyl antibodies were indeed responsible, because priming with RAT and boosting with BI-2 did not induce IgG formation. Accordingly, the observations that IgG responses in RAT-primed mice were induced only by TRI and not by any of the bifunctional antigens indicate that two carrier epitopes per antigen molecule are indeed required for IgG induction. They also provide indirect evidence for synergistic help in the switching of immunoglobulin isotypes.

Murine B-cell subpopulations responsive to T-dependent and T-independent antigens.

Strain A/J mice made secondary indirect plaque-forming cell (PFC) responses to azobenzenearsonate (ABA) conjugates of giant keyhole limpet hemocyanin (KLH), a thymic-dependent antigen, but not to conjugates of Ficoll, a T-independent antigen. ABA-Ficoll was also unable to elicit a response in animals primed with ABA-KLH, which have an expanded anti-ABA memory cell pool. On the other hand, ABA-Ficoll rendered mice unresponsive to ABA-KLH when administered before priming or boosting with the T-dependent immunogen. Hence, the T-independent antigen was able to tolerize but unable to trigger B-memory cells responsive to the T-dependent antigen. A/J mice immunized with dinitrophenyl conjugates of Ficoll or bovine IgG (BGG) made vigorous IgM and IgG PFC responses. PFC responses to ABA-KLH and 2,4-dinitrophenyl (DNP)-BGG were abrogated by depleting mice of C3 with cobra venom factor, whereas the IgM and IgG PFC responses to DNP-Ficoll were unaffected. B lymphocytes were fractionated on the basis of receptors for C3 and the subpopulations were assayed for in vitro PFC responses to DNP-Ficoll. Very little response was obtained from complement receptor lymphocyte [CRL(+)] B cells, whereas CRL(-) cells were more responsive than unfractionated B cells. Both populations responded to a polyclonal B-cell mitogen (lipopolysaccharide). On the other hand, the in vitro PFC response to a T-dependent antigen (sheep erythrocytes) correlated with the presence of CRL(+) B cells in the cultures. However, a minor component of this response, sensitive to anti-Thy-1 serum, was made by CRL(-) B cells, indicating the existence of subpopulations of T-dependent B cells with different signalling requirements. The results suggest that most B cells responsive to T-dependent antigens possess receptors for C3 and that C3 plays an obligatory role in the response of these cells. A distinct subpopulation of B cells which lack C3 receptors respond to T-independent antigens. The precursors of PFC for the ABA epitope reside largely or exclusively in the CRL(+) compartment in A/J mice, whereas precursors for the DNP determinant are found in both compartments.

Idiotype profile of an immune response. II. Reversal of the relative dominance of major and minor cross-reactive idiotypes in arsonate-specific T-independent responses.

Two different cross-reactive idiotype (CRI) groups are distinguishable in the Ab response of A/J mice to the p-azobenzenearsonate (ABA) hapten: CRIA and CRIm. These two groups showed distinct patterns of relative dominance in the ensuing response depending on whether the inducing Ag was a T cell-dependent (TD) form of ABA, such as ABA-KLH or ABA-CGG, or a T-independent type 1 (TI-1) form, such as ABA-Brucella abortus or ABA-lipopolysaccharide (LPS), and on whether the response was elicited in vivo or in vitro. The CRI+ component of primary in vivo plaque-forming cell (PFC) responses to TD ABA Ags was largely (greater than 90%) CRIA+ as was, to a slightly lesser extent (greater than 75%) the CRI+ portion of secondary or hyperimmune serum Ab or PFC responses to the same Ags. In contrast, in vivo primary and hyperimmune PFC responses to ABA-Bru or ABA-LPS showed a significantly lower CRIA/CRI ratio, averaging 0.5-0.6, with some individual mice giving figures as low as 0.2, indicating predominance of CRIm over CRIA. Serological analysis of hyperimmune anti-ABA Abs from a group of 5 A/J mice immunized with ABA-Bru gave a figure of less than 0.5 for the CRIA/CRI ratio. The most striking disparity from the TD pattern was seen in primary in vitro PFC responses to the TI ABA Ags; here ratios of less than 0.2 were generally seen. Since T cell removal did not alter the Id pattern in the TI responses, CRIA-specific Ts cells do not account for the weak expression of CRIA in such responses. We propose a model that explains these results on the basis of differential expression of IdX dominance by two distinct B cell subpopulations--equatable to the Lyb-5+ and Lyb-5- B cell subsets--along with differential relative activation of these subsets in different types of responses. Examination of anti-ABA PFC responses of F1 progeny of CBA/N and A/J mice to ABA-Bru lends support to this hypothesis since CRIA expression was significantly lower in mice with the xid defect.

Arsonate-specific murine T cell clones. I. Genetic control and antigen specificity.

The antigen-induced proliferative response of lymph node cells (LNC) from mice sensitized to the monofunctional antigen L-tyrosine-p-azobenzenearsonate (ABA-Tyr) was used to monitor genetic control. All strains tested mounted significant responses, but those that were H-2(b) at both the I-A and I-E loci [B10., B6., B10.A(18R), A.BY, and C3H.SW] gave consistently weaker responses than other haplotypes. The F(1) progeny of matings between high and low responder phenotype parents (DBA/2 and B6, respectively) were high responders, establishing the dominance of the responder trait. Proliferative responses of LNC to ABA-Tyr were blocked by the appropriate anti-Ia monoclonal reagents. For example, B10.A(4R) LNCI (I-A(k), I-E(b)) were blocked by anti-I-A(k), whereas B10.A(3R) LNC (I-A(b), I-E(k)) were blocked by anti-I-E(k). Long-term cultures of T cell lines specifically reactive to ABA-Tyr were established from LNC of A/J mice immunized with ABA-Tyr and were cloned by limiting dilution. The proliferative responses to ABA-Tyr of 14 out of 15 clones tested were I-A restricted on the basis of activation by antigen-presenting cells from appropriate recombinant strains and the blocking activity of the monoclonal anti-Ia antibodies. The response of the other clone was I-E restricted. The fine antigen specificity of the clones was studied using structural analogs of the homologous antigen to induce proliferation. The clones could be divided into three types with respect to responsiveness to ABA-histidine (ABA-His). One group responded about equally well to ABA-His and ABA-Tyr. A second set responded less strongly to ABA-His than to ABA-Tyr, while the third showed no response above background to ABA- His. In all instances, the ABA-His-responding clones discriminated exquisitely between the 2-azo and 4-azo histidine isomers, responding only to the 4-azo compound. These T cell clones provide extremely useful tools for studies of T cell specificity, antigen recognition and lymphoid cell interaction systems.

Antigen recognition and the immune response. Structural requirements in the side chain of tyrosine for immuno-genicity of L-tyrosine-azobenzenearsonate.

The low molecular weight compound L-tyrosine-azobenzenearsonate (RAT) induces a cellular immune response in guinea pigs. The contribution of the side chain of tyrosine to the immunogenicity of RAT and the structural requirements at that position for immunogenicity were assessed by synthesizing a series of analogs of RAT containing modifications in the side chain of tyrosine and employing them as immunogens. Removal of either the carboxyl or amino group did not markedly affect immunogenicity, measured by the induction of delayed cutaneous sensitivity, whereas deletion of both completely abolished it. However, a charged group was not required since side chains containing a polar hydroxyl group could substitute for chains bearing an amino or carboxyl group. The size of the side chain exerted a pronounced influence; the charged or polar substituent had to be extended from the phenolic ring by at least two carbon atoms in order to confer immunogenicity.

Antigen recognition and the immune response. "Self-help" with symmetrical bifunctional antigen molecules.

L-Tyrosine-p-azobenzenearsonate (RAT) induces cellular immunity without humoral antibody in guinea pigs. Asymmetric bifunctional antigens composed of one RAT moiety and one dinitrophenyl (DNP) group separated by flexible spacers induce anti-RAT cellular immunity and an anti-DNP humoral response. Symmetrical bifunctional antigens of similar design but comprised of two RAT determinants induce cellular immunity without demonstrable anti-RAT antibody. However, when the flexible spacer is replaced by a rigid decaproline chain, humoral anti-RAT responses are provoked. Since RAT contains both electropositive (azo) and electronegative (arsonate) centers, the failure of bifunctional RAT compounds with flexible spacers to induce humoral immunity might be ascribed either to intramolecular stacking, which compromises their bifunctional character, or to interaction of both determinants with receptors on the same cell surface, which would fail to satisfy the requirement for cooperation. In order to distinguish between these alternatives, symmetrical bifunctional antigens composed of two L-tyrosine-p-azophenyltrimethylammonium (TAT) determinants separated by flexible or rigid spacers were synthesized. TAT is immunogenic and does not cross-react with RAT. Furthermore, it contains only electropositive centers and consequently bifunctional molecules do not undergo intramolecular stacking. Immunization with either flexibly or rigidly spaced bifunctional TAT antigens raised anti-TAT antibody. These results conclusively demonstrate that "self-help," cooperation between bone marrow-derived and thymus-derived lymphocytes of identical or similar specificity, can occur, provided the determinants on the antigen are prevented from associating with each other.

Antigen recognition and the immune response. Humoral and cellular immune responses to small mono- and bifunctional antigen molecules.

L-Tyrosine azobenzene-p-arsonate (RAT) induced cellular immunity without antibody production in guinea pigs. Bifunctional antigens were prepared consisting of one RAT carrier moiety linked either directly to a dinitrophenyl (DNP) haptenic determinant or through one or more 6-amino-caproyl (SAC) spacers. Each SAC unit has an extended span of 8 A. Guinea pigs immunized with these conjugates developed cellular immunity directed against the RAT determinant and antibody specific for the DNP determinant. The anti-DNP response was the same with one or three SAC spacers, but was significantly weaker when the two determinants were joined without a spacer. Animals immunized with either DNP-SAC-TYR or DNP-TYR developed neither cellular nor humoral immunity. Prior immunization with RAT potentiated the secondary anti-hapten response to DNP-SAC-RAT. Modification of RAT at either the arsonate or tyrosine positions showed that other charged groups (sulfonate and trimethylammonium) could substitute for arsonate without loss of immunogenicity. Removal of either the amino or carboxyl group from the side chain of tyrosine did not abolish immunogenicity, but immunogenicity was lost upon removal of both. Immunization with symmetrical bifunctional RAT-(SAC)(n)-RAT and cyclo-(L-RAT-D-RAT) antigens led to cellular immunity but no anti-arsonate antibody, suggesting a barrier to "self-help." These compounds were also ineffective in inducing a secondary anti-arsonate response in animals primed with arsonate-BSA conjugates and RAT.

Immunogenicity of glucagon: determinants responsible for antibody binding and lymphocyte stimulation.

Bovine glucagon, a polypeptide of 29 amino acids, is immunogenic in rabbits and guinea pigs. The antigenic determinants of glucagon were investigated with isolated tryptic peptides of the hormone. Antibodies from virtually all of more than a dozen animals tested had specificity primarily for the aminoterminal heptadecapeptide. However, only intact glucagon and its carboxy-terminal dodecapeptide stimulated spleen or lymph node cells to synthesize DNA. It thus appears that glucagon was cleaved along functional lines into two parts, one of which contained the major antigenic determinant for serum antibody and the other of which was "recognized" by antigen-reactive cells.

The murine T-lymphocyte response to tyrosine-azobenzenearsonate. Characteristics of a low responder haplotype T-cell clone.

An I-Ab-restricted, L3T4+ Ly2- T-cell clone, 5R-4F3, specific for ABAtyr was established in culture from a B10.A(5R) mouse. Since b haplotype mice respond weakly to ABAtyr compared to other haplotypes, this is a candidate clone of low responder phenotype. In support of this contention, 5R-4F3 grew very poorly under conditions that supported the vigorous growth of E beta bE alpha k-restricted T-cell clones from the same mouse. The I-A (low responder) and I-E (high responder) restricted T-cell clones also differed in their responses to apc pre-pulsed with antigen, compared to apc with antigen present continuously during culture. The low and high responder clones responded comparably to IL-2. Attempts to elevate the response of C57BL/6 mice to ABAtyr in vivo by injecting them with human recombinant IL-2 and antigen together were only partially successful: C57BL/6 mice treated in this way showed a 3-5-fold increase in their proliferative responses to ABAtyr, which was at best only one quarter of the level of response shown by high responder A/J mice to the same antigen dose.

Immunogenicity of biotinylated hapten-avidin complexes.

The efficacy of avidin as a carrier for the generation of anti-hapten antibodies was assessed in mice by immunization with complexes of avidin and synthetic peptides containing biotin and an epsilon-dinitrophenyl (DNP) lysine residue. The synthetic haptens were constructed with 0, 1 or 2 6-aminocaproyl groups as spacers between the biotin and DNP-lysine moieties. Complexes without a spacer did not induce anti-DNP antibody responses, while those with two spacers induced stronger responses than those with only one spacer. However, the anti-DNP responses to avidin-biotinylated hapten complexes were considerably weaker than responses to a conventional hapten-protein conjugate (DNP-ovalbumin), and, like "T-independent" antigens, failed to induce significant immunological memory. The distribution of isotypes in the anti-DNP antibodies produced to avidin-biotin-6-aminocaproyl-epsilon-DNP-lysine-alanine and DNP-ovalbumin was similar, but the former antigen induced significantly lower levels of antibody in (CBA/N X BALB/c) F1 male mice with the xid defect than in phenotypically normal female littermates, and also induced significant responses in nu/nu mice, in contrast to DNP-ovalbumin. These findings suggest that there is at least a "T-independent" or "T-efficient" component in the response to avidin-biotin complexes, perhaps due to the tetrameric structure of the molecule. Estimates of the depth of the receptor site for biotin were obtained by using the complexes to competitively inhibit the binding of anti-DNP antibody to plates coated with DNP-protein. The findings were consonant with the data on immunogenicity (capacity to induce anti-DNP antibody responses) and suggested that the receptor site has a depth of 16-26 A.

Differential induction of help and suppression in mice by bifunctional antigens administered via different routes.

Bifunctional antigens composed of one L-tyrosine-p-azobenzenearsonate (Tyr-ABA) carrier epitope and one dinitrophenyl (DNP) haptenic epitope separated by 6-aminocaproyl or polyprolyl spacers induced weak IgM anti-DNP plaque-forming cell (PFC) responses in the spleens of mice immunized intraperitoneally, without detectable IgG PFC. However, the same antigens introduced into the footpads induced IgG PFC responses in the draining lymph nodes which rose to levels greater than 100/10(6) viable lymphocytes. Moreover, the response in the lymph nodes to booster injections of antigen was characteristic of secondary T-dependent antibody responses, whereas the splenic secondary response simply mirrored the primary. The magnitude of the IgG PFC response was influenced by the size of the spacer and by the strain of mice, although genetic control did not map to the major histocompatibility complex. Prior i.p. immunization suppressed the IgG response to subsequent immunization in the footpads. This suppression could be transferred to normal syngeneic recipient mice with spleen cells from suppressed donors. Suppressor activity was eliminated by treating the spleen cells with anti-Thy-1 antibody prior to transfer, establishing the T-cell dependency of suppression. Suppression was also induced by Tyr-ABA itself, but not by DNP-lysine, indicating the epitope specificity of the suppressor cells. Thus, bifunctional antigens induce dominant suppression in the spleen but significant help in lymph nodes.