Auxotrophic vaccines for tuberculosis.

Tuberculosis is responsible for the deaths of more people each year than any other single infectious disease, with greater than 7 million new cases and 2 million deaths annually. It remains the largest attributable cause of death in HIV-infected individuals, responsible for 32% of deaths of HIV-infected individuals in Africa. The only currently available vaccine for tuberculosis, bacille Calmette-Guerin (BCG) is the most widely used vaccine in the world, being administered to approximately 100 million children each year. Although untoward effects were not seen in several studies of HIV-seropositive children, the safety of live attenuated BCG vaccine in HIV-positive adults remains unknown and a matter of some concern. To obviate potential adverse affects of BCG vaccines in immunodeficient individuals, we have studied five auxotrophic strains of BCG produced by insertional mutagenesis for safety in administration to mice with severe combined immunodeficiency disease (SCID), and for protection in a susceptible strain of mice. The results indicate that viable BCG could no longer be detected in mice receiving the auxotrophs after 16-32 weeks, and that infected SCID mice survived for at least 230 days. In contrast, all SCID mice succumbed within eight weeks to conventional BCG vaccine. When susceptible BALB/c mice were immunized with auxotrophs and subsequently challenged with virulent Mycobacterium tuberculosis, several of the auxotrophs produced comparable protection against intravenous and intratracheal challenge with M. tuberculosis relative to conventional BCG. These results suggest that auxotrophic strains of BCG represent a potentially safe and useful vaccine against tuberculosis for populations at risk for HIV.

Requirement for T cells in the production of migration inhibitory factor.

The question whether B lymphocytes are capable of being activated by antigen in the absence of functional T cells was investigated in a model that excludes participation of T cells by virtue of an immune response gene restriction. Strain 2 guinea pigs are capable of responding to immunization with DNP-PLL, whereas strain 13 animals are not. In the present experiments, animals of both strains were immunized with DNP-PLL complexed to ovalbumin (DNP-PLL-Ova) under conditions in which equal titers of antibodies to DNP were produced by both strains. The failure of T cells of strain 13 animals to respond to DNP-PLL was confirmed by the virus plaque assay. While spleen cells from both strains produced MIF after stimulation with DNP-PLL-Ova, in response to DNP-PLL only strain 2 spleens were able to produce MIF. Cells from neither strain could be activated by DNP-guinea pig albumin to produce MIF. We conclude that B lymphocytes are incapable of being stimulated by antigen in the absence of T cells, and that MIF production is a thymus-dependent response. While the results indicate that MIF production is a valid qualitative assay for T-cell competence, since MIF can be produced by B and T cells, the degree of migration inhibition cannot be regarded as a quantitative measure of T-cell function.

Products of activated lymphocytes. I. The use of radiolabeling techniques in the characterization and partial purification of the migration inhibition factor of the guinea pig.

General methods were developed and applied to the biosynthesis and purification of products of activated lymphocytes available in minute quantities. The activity studied here was the migration inhibitory factor (MIF) produced by purified protein derivative (PPD)- or concanavalin A (Con A)-stimulated lymphocytes obtained from one guinea pig or less. The methods selected yielded results in terms of two chemical parameters characteristic of the molecules involved, namely K(d) on Sephadex G-75 and isoionic point, pI, on isoelectric focusing. When supernatants were fractionated on G-75 columns, there were several areas even in control supernatants which produced migration inhibition relative to medium controls. However, in PPD- and Con A-stimulated supernatants, at least one peak of MIF activity was found solely in the stimulated cultures, with a K(d) of 0.15. A double-labeling technique was used to characterize the proteins of this peak. Control, unstimulated cultures were labeled with [(14)C]leucine and stimulated cultures were labeled with [(3)H]leucine. After mixing the supernatants and G-75 filtration, a major "ratiolabeled" broad peak. i.e. one with increased (3)H/(14)C ratio, was found. When a narrow portion of this peak about K(d) 0.15, containing most of the MIF activity, was subjected to analytical isoelectric focusing, all of the label was associated with proteins of lower net charge than albumin. A unique ratiolabeled peak was found in PPD- and Con A-stimulated fractions with a pI of approx. 5.3. A micropreparative isoelectric focusing technique was developed and yielded MIF activity in the same region as the major ratiolabeled peak. Further study will be required to ascertain whether the ratiolabeled protein is MIF. By following the K(d), pI, and (3)H/(14)C labeling ratio, at least 14 products of activated lymphocytes, synthesized either de novo or in increased amounts, could be distinguished.

A T helper cell 2 (Th2) immune response against non-self antigens modifies the cytokine profile of autoimmune T cells and protects against experimental allergic encephalomyelitis.

Experimental allergic encephalomyelitis (EAE) is an autoimmune disease of the central nervous system (CNS), and the most commonly used experimental model for multiple sclerosis. It is mediated by autoreactive T cell clones exhibiting a T helper cell (Th) 1 cytokine profile. Nonencephalitogenic T lymphocytes specific for self or exogenous antigens have been found to suppress encephalitogenic T cell responses and to protect against autoimmune disease. The mechanisms by which exogenous antigens modulate autoimmunity are not fully understood. In this study, we tested the hypothesis that a Th2-type immune response against an exogenous, nonself antigen, keyhole limpet hemocyanin (KLH), by releasing IL-4 in the microenvironment, could shift the cytokine profile of encephalitogenic T cells from an inflammatory Th1 to a protective Th2 type. SJL/J mice were preimmunized with the KLH in incomplete Freund's adjuvant to induce a population of Th2 memory cells that would be expected to release Th2 cytokines when activated by the specific antigen at the time of EAE induction. Four weeks later, mice received an encephalitogenic challenge containing guinea pig myelin in complete Freund's adjuvant with or without KLH. All KLH primed animals not receiving the exogenous antigen at the time of EAE induction developed a severe clinical disease indistinguishable from control mice not KLH primed. In contrast, animals preimmunized and challenged with the encephalitogenic inoculum containing KLH showed either no, or markedly reduced, clinical signs. Enzyme-linked immunospot analysis demonstrated that KLH-specific T cells in the primed mice were producing IL-4 characteristic of Th2 cells. In the KLH-primed and restimulated mice, the cytokine profile of the autoreactive, myelin basic protein-specific T cells was shifted from an inflammatory Th1 towards a protective Th2 type. We infer that the presence of IL-4 secreted by KLH-specific memory Th2 cells in the lymphoid system microenvironment in which the autoreactive T cells were engaged by the encephalitogenic stimulus were able to bias their cytokine profile towards a protective Th2 phenotype. This interpretation is supported by the observation that the protective effect of preimmunization with KLH was overcome by rm-IL-12, which inhibited the production of IL-4 by the Th1 cells and biased the autoimmune response to a predominantly Th1 type. Since IL-4 mRNA could not be detected by reverse transcriptase PCR in the CNS, the protective effect was inferred to be mediated by Th2 cells in the lymphoid system, and not the target organ. We conclude that exogenous, nonself antigens that can induce Th2 responses, can modify the cytokine environment sufficiently to alter the cytokine phenotype of inflammatory, autoreactive T cell clones, and ultimately, to provide significant protection against EAE and possibly other T cell-mediated autoimmune diseases.

Differentiation of memory T cells to virus plaque-forming cells and cytotoxic T lymphocytes.

The aims of this study were to define the T-cell subpopulation(s) detected by the virus plaque assay, and particularly to determine whether the virus plaque assay could be used to enumerate cytotoxic T lymphocytes. In addition, studies were undertaken to ascertain whether cell proliferation was required for development of cytotoxic effector function and virus plaque formation by these subpopulations. The results of experiments with a secondary mouse mixed lymphocyte culture (MLC) model indicated that 70 percent of virus plaque-forming cells bore the Ly 1 phenotype and 30 percent the Ly 2,3 phenotype. Three lines of evidence suggested that cytotoxic T lymphocytes (CTL) can be detected by this assay: the fact that some virus plaque-forming cells (V-PFC) bear the same Ly phenotype as CTL; the use of an inhibitor of DNA synthesis indicated that proliferating cells could be eliminated with no effect on V-PFC production and cytotoxic activity of the Ly 2,3 cell population; and that infection of primed lymphocyteswith vesicular stomatitis virus before (MLC) stimulation eliminated cytotoxic activity. In primary MLC, development of V-PFC and CTL was completely abolished by cytosine arabinoside. In contrast, in secondary MLC, some CTL and V- PFC were generated by antigenic stimulation in the absence of proliferation. However, the development of both functions became progressively more susceptible to cytosine arabinoside as the time between primary immunization and in vitro boosting is increased. It is suggested that there may be a considerable disparity between the number of existing effector cells at any given time and the cytotoxic potential, i.e. the number of cells capable of being generated by antigenic stimulation.

Primary demyelination as a nonspecific consequence of a cell-mediated immune reaction.

Primary demyelination occurs in a variety of human and experimental diseases known to be associated with the presence of inflammatory cells. However, the mechanism of demyelination remains unclear. The possibility that myelin can be damaged as a nonspecific consequence of a specific delayed type of hypersensitivity reaction directed at nonnervous tissue antigens was investigated. Guinea pigs were sensitized to tuberculin with Freund's complete adjuvant, and were challenged in the central and peripheral nervous system either with live or killed sonicated tubercle bacilli, Old Tuberculin, or tuberculin purified protein derivative (PPD). Local inflammatory reactions were invariably produced and primary demyelination was a constant feature of the lesions. The morphological picture was rather similar to that observed in human neurotuberculosis and early tuberculoid leprosy, and in experimental allergic encephalomyelitis and distemper encephalitis in animals. The infiltrates consisted predominantly of mononuclear cells with some polymorphonuclear cells as well. Vesicular disruption of the myelin sheath in the immediate vicinity of the inflammatory cells and stripping of the myelin lamellae by the histiocytes without axonal damage were the leading features of the lesion. The results indicate that cell-mediated immune reactions to a variety of nonbrain antigens could be responsible for a component of the demyelination seen in some inflammatory demyelinating conditions, and suggest that this system may serve as a useful model for studying the immunopathology of demyelinating disease.

On the relation of products of activated lymphocytes to cell-mediated cytolysis.

Experiments have been designed to test the hypothesis that soluble mediator production and T-cell-mediated cytotoxicity are necessarily related phenomena, and that soluble mediators may be involved in the mechanism of cytolysis. To this end, agents known to inhibit T-cell-mediated lysis in vitro have been studied for their effects on the production of two lymphocyte-derived mediators, lymphotoxin (LT) and migration inhibitory factor (MIF). A clear dissociation between mediator production and cell-mediated cytolysis was found using inhibitors of protein synthesis. Pactamycin and emetine, in doses of 10(-7) M to 10(-6) M, suppressed production of MIF and LT with only slight effect on killing of mastocytoma cells by immune T cells. On the other hand colchicine and vinblastine inhibited T-cell-mediated cytolysis in a dose-related manner but had no significant effect on either MIF or LT production, A striking dichotomy was also observed after augmentation of intracellular cyclic 3'5' adenosine monophosphate (cAMP) levels with cholera enterotoxin. Increased cAMP levels were associated with abrogation of direct lytic activity, but were without significant effect on MIF or LT production in guinea pigs or mice. These findings indicate that mediator production and direct lymphocyte-mediated cytolysis can be experimentally dissociated and represent independent cell-mediated immune functions.

A plaque assay for enumerating antigen-sensitive cells in delayed-type hypersensitivity.

A general method is described for enumerating antigen-sensitive lymphocytes obtained from individuals having delayed hypersensitivity, in this case from highly tuberculin-sensitive guinea pigs. The method is based on the observation that resting lymphocytes are generally unable to support replication of RNA viruses, whereas antigen-"activated" lymphocytes can. Lymph node lymphocytes from individual animals were cultured in the presence or absence of tuberculin purified protein derivatives (PPD). After various periods of time, the cells were infected either with Newcastle disease virus or vesicular stomatitis virus, and plated in agar over a monolayer of cells susceptible to the virus. Wherever a lymphocyte yielded infectious virus, a discrete plaque in the monolayer could be seen. The increase in plaques of the antigen-stimulated cells over the background of the control sample was taken as the number of antigen-sensitive cells in the population. When lymphocytes from normal guinea pigs or from guinea pigs immunized to produce only circulating antibody to PPD were similarly tested, no increase in plaque-forming units (PFU) was observed. The average increase in PFU due to antigenic stimulation varied from 1 per 1000 lymphocytes at 24 hr to 16 per 1000 lymphocytes at 96 hr. By employing inhibitors of mitosis (colchicine, vinblastine, and thymidine) it was evident that the increase in PFU at least up to 48 hr was primarily due to initial antigen-reactive cells and not their progeny.

Isolation of variants in phagocytosis of a macrophage-like continuous cell line.

We have isolated cloned variants in phagocytosis from a cloned continuous murine macrophage-like cell line, J 774.2. A selection procedure against Fc receptor-mediated phagocytosis was devised using IgG-coated SRBC containing a toxic drug, tubercidin, as the lethal agent. A series of variant clones deficient in Fc receptor-mediated phagocytosis were isolated. Such variants occurred at low frequency (approximately 6 X 10(-5)), were stable, and appeared to possess Fc receptors. The degree to which they were defective in phagocytosis of IgG-coated SRBC varied from clone to clone, yet all clones, were able to phagocytize latex particles. The phagocytic defect in some variants could be corrected by the addition of 8 Br-cAMP, in others, the drug was without effect. It is likely, therefore, that different variants are defective in several distinct steps critical to Fc receptor-mediated phagocytosis.

On the heterogeneity of murine natural killer cells.

The heterogeneity of cells capable exerting spontaneous cytotoxicity in vitro was explored using antisera to several genetically determined surface markers on mouse lymphocytes. Four phenotypes of cells derived either from fresh or cultured murine lymphoid tissue were found to exert natural killer (NK) activity in vitro. One affector cell subset, termed NKI cells, had the serological phenotype of Thy-1-, Lyt-2-, Qa5+, and lysed measles virus persistently infected target cells (HeLa-Ms) but not P815 mastocytoma cells. It corresponds with the NK cells described in most systems in which lymphoma targets are commonly used. A second subset, with the same target cell specificity, termed NKT is a thymus-independent cell with the phenotype Thy-1+, Lyt-2-, Qa-5+, Ly-5+. A third subset of NK cells, termed T killer (TK) cells deriving from cultures of conventional but not nude mouse spleens, mediated spontaneous cytotoxicity of P815 mastocytoma cells, but not of virus-infected targets. It has a phenotype of Thy-1+, Lyt-2+, Qa-5-, Ly-5+, apparently identical with that of conventional, antigen-specific cytotoxic T lymphocytes. The fourth phenotype of NK cells, termed NKM, derived primarily from cultures of bone marrow, is cytotoxic for HeLa-measles but not P815, and expresses only Ly-5+ among the various markers tested. Beige mice possess normal TK and NKM activities, but had normal NKI, NKT as well as NKM activity. All NK cell subsets express the Ly-5 surface marker. The existence of four phenotypically distinct NK effector cells was strengthened by studies on selective regulation of their activity by two different biological factors. Interferon (IFN) augmented NK activity of primarily one of the subsets examined, the NKI cell; the activity of IFN on NKT cells could not be directly tested, but IFN was without positive effect on TK or NKM cells. In contrast, partially purified IFN-free interleuken 2 (IL-2) augmented the activities of both the TK and NKT subsets, but not of NKI or NKM cell. IL-2 was active in augmenting NK activity in spleen cells obtained from both conventional and nu/nu mice, but was without effect on spleens of nu/nu mice depleted of Thy-1+ cells. These and other data suggest that IL-2 acts primarily, if not exclusively, on THy-1+ cells. These results strengthen the view that natural cytotoxicity in vitro can be mediated by several distinct cell populations under different genetic and regulatory control and indicate the importance of defining and delineating the cell lineages of each and the role of the independent subsets in resistance to virus infections and tumors in vivo.

Selective viral immunosuppression of the graft-versus-host reaction.

Graft-vs.-host (GVH) reactivity of parental lymph node (LN) cells was assayed by measurements of 3H-thymidine incorporation in vivo in spleens of irradiated F1 recipients. Preincubation of parental LN cells with vesicular stomatitis virus (VSV) for 2 h at 37 degrees C followed by washing resulted in an 85-90% reduction in splenic radioactivity, as did injection of VSV on days 0-2 after recipients received untreated parental LN cells. In contrast, 3H-thymidine incorporation in the spleens or irradiated F1 hosts was not affected by VSV when F1 bone marrow cells were incubated with the virus. In addition, preincubation of F1 B cells with VSV still allowed these syngeneic B cells to be recruited into proliferation by mitomycin-treated parental LN cells. The inhibitory effect of VSV, thus, seems to be specific for T-cell proliferation. These observations suggest that viral immunosuppression might be capable of being developed into a useful strategy for selective deletion of lymphocytes capable of reacting against histocompatibility antigens and initiating GVH reactions.

Mode of regulation of natural killer cell activity by interferon.

Whereas xenogeneic tumors such as baby hamster kidney or HeLa cells grow in nude mice, the same cells persistently infected with a variety of viruses are rejected. Spleen cells from normal nude mice were found to be induced to produce interferon and to exert natural killer (NK) activity on virus persistently infected (PI) tumor cells, and not on uninfected parental cells in vitro. The phenotype of the interferon-producing cells and the NK effector cells was found to be the same namely, Qa 5(+), Ly 5(+), ganglio-N- tetraosylceramide, with 35 percent of the NK cells also expressing Thy 1.2. NK activity against virus PI tumor cell lines could be nonspecifically augmented both in vivo and in vitro by prior contact with virus PI tumor cells. It was unambiguously demonstrated with chemically homogeneous mouse interferon that interferon, and not a contaminant, was responsible for the augmentation of NK activity in vitro. Studies on the mode of interferon action in augmenting NK activity revealed that the target cell for interferon action was serologically distinct from the NK effector cell. Anti-Ly 5 + complement (C)-treated spleen cells were depleted of NK activity and the ability to produce interferon, but, upon incubation with interferon for 1-3 h, regained both NK activity and susceptibility to anti-Ly 5 + C. Treatment with anti-Qa 5 + C eliminated NK activity, which could not be restored by the addition of interferon. We conclude that interferon produced by Ly 5(+) cells in response to virus PI tumor cells acts on Ly 5(-) precursor cells and induces their differentiation into functional Ly 5(+) NK effector cells.

On the number and nature of antigen-sensitive lymphocytes in the blood of delayed-hypersensitive human donors.

The virus plaque assay has been successfully employed to enumerate antigen-sensitive cells in the peripheral blood lymphocyte populations of tuberculin-hypersensitive human donors. The method is based on the finding that, while resting lymphocytes are unable to produce a variety of viruses upon infection, lymphocytes activated by specific antigens become capable of virus replication. The average number of antigen-sensitive cells detected in cell populations from donors reacting to first test strength or intermediate test strength tuberculin was approximately 3.6/1000 lymphocytes, and the averages for both groups were similar. Studies on the kinetics of appearance of these virus plaque-forming cells and on the effects of the mitotic inhibitor, vinblastine, indicate that the activation of these antigen-sensitive cells is a linear process and that the cells must be nondividing cells during this process. These qualities contrast markedly with those described for the mitogenic response and the antibody-producing cells which require cell division and increase exponentially. On the basis of these experiments it is suggested that the antigen-sensitive cell measured in the virus plaque assay is the effector cell in delayed-type hypersensitivity reactions and, in addition, may be one of the cells critically involved in antibody formation.

The production of vesicular stomatitis virus by antigen- or mitogen-stimulated lymphocytes and continuous lymphoblastoid lines.

A variety of lymphoid cell populations were examined in terms of their ability to replicate vesicular stomatitis virus (VSV), a lytic, RNA-containing virus maturing at the cell surface. The number of cells capable of producing VSV was estimated in terms of infectious centers by the virus plaque assay (VPA), and morphologically by electron microscopy (EM). The lymphoid cells examined in this study included: (a) lymph node cells from delayed hypersensitive guinea pigs stimulated by specific antigen, (b) mouse spleen cells activated by selective bone marrow-derived (B) cell and thymus derived (T) cell mitogens, and (c) cells of human and murine continuous lymphoblastoid or lymphoma lines. In unstimulated cultures of guinea pig lymph node cells there is a background of approximately 1 in 1,000 cells which produces VSV; in purified protein derivative (PPD)-stimulated cultures the number of cells producing virus was 1.6% in the VPA and 1.9% by EM. These cells were large lymphocytes with some morphological features of transformed lymphocytes but were not typical blast cells. A few macrophages were associated with virus in both stimulated and control cultures. These observations indicate that (a) cells responsive to antigens, as detected by a marker virus, were lymphocytes; (b) cells other than lymphocytes (macrophages) were capable of replicating VSV even without antigenic stimulation; and (c) the correlation of results obtained by VPA and morphologic examination was usually quite good. Of the total number of mouse spleen cells stimulated with concanavalin (Con A), a T cell mitogen, 4.5 (EM)-5.7% (VPA) were associated with VSV. These were characteristic transformed lymphocytes, similar to phytohemagglutinin (PHA)-stimulated human lymphocytes. In contrast Escherichia coli lipopolysaccharide (LPS)-treated mouse spleen cultures contained lower numbers of virus plaque-forming cells. The majority of such cells associated with virus displayed extensive rough endoplasmic reticulum. Two cultured murine lymphomas containing lymphocytes with the theta surface marker (L5178Y and EL-4) showed a 15-100-fold higher incidence of virus-producing cells than leukemias (L1210 and C57Bl/6) which did not carry this marker. Similarly, the L2C guinea pig leukemia, a known B cell leukemia, yielded a low percent of virus plaque-forming cells (<2%). However, MOPC-104, a plasma cell tumor presumed to be of B cell origin, was found to be an efficient virus producer. There was a wide variation in the efficiency of VSV replication among human lymphoblastoid lines. One line, Wil-2, produced 80% infectious centers after 24 h of exposure to VSV, and all cells were associated with virus at the EM level. The relationship between the virus-producing cells and different lymphocyte subpopulations as well as the efficiency of the two assays for studying virus-producing lymphocytes is discussed.

Killing of virulent Mycobacterium tuberculosis by reactive nitrogen intermediates produced by activated murine macrophages.

Tuberculosis remains one of the major infectious causes of morbidity and mortality in the world, yet the mechanisms by which macrophages defend against Mycobacterium tuberculosis have remained obscure. Results from this study show that murine macrophages, activated by interferon gamma, and lipopolysaccharide or tumor necrosis factor alpha, both growth inhibit and kill M. tuberculosis. This antimycobacterial effect, demonstrable both in murine macrophage cell lines and in peritoneal macrophages of BALB/c mice, is independent of the macrophage capacity to generate reactive oxygen intermediates (ROI). Both the ROI-deficient murine macrophage cell line D9, and its ROI-generating, parental line J774.16, expressed comparable antimycobacterial activity upon activation. In addition, the oxygen radical scavengers superoxide dismutase (SOD), catalase, mannitol, and diazabicyclooctane had no effect on the antimycobacterial activity of macrophages. These findings, together with the results showing the relative resistance of M. tuberculosis to enzymatically generated H2O2, suggest that ROI are unlikely to be significantly involved in killing M. tuberculosis. In contrast, the antimycobacterial activity of these macrophages strongly correlates with the induction of the L-arginine-dependent generation of reactive nitrogen intermediates (RNI). The effector molecule(s) that could participate in mediating this antimycobacterial function are toxic RNI, including NO, NO2, and HNO2, as demonstrated by the mycobacteriocidal effect of acidified NO2. The oxygen radical scavenger SOD adventitiously perturbs RNI production, and cannot be used to discriminate between cytocidal mechanisms involving ROI and RNI. Overall, our results provide support for the view that the L-arginine-dependent production of RNI is the principal effector mechanism in activated murine macrophages responsible for killing and growth inhibiting virulent M. tuberculosis.

Occurrence of restricted suppressor T-cell activity in man.

Blood leukocytes from an immunologically hyporesponsive patient with urinary bladder carcinoma were found to be deficient in their ability to stimulate 3 of 27 responder leukocyte preparations from normal individuals in one-way mixed leukocyte culture (MLC). The patient's T-depleted leukocytes, however, functioned adequately as stimulator cells. T-enriched lymphocytes from this patient suppressed the MLC responsiveness of those three normals but not the responsiveness of other normals. The patient's cells suppressed the MLC responsiveness of only one of each of the parents of two of the normals who could be suppressed by the patient's leukocytes suggesting a possible genetic restriction to this suppressor cell activity.

Isolation of a heterogeneous population of temperature-sensitive mutants of measles virus from persistently infected human lymphoblastoid cell lines.

Two human lymphoblastoid B-cell lines, WI-L2 and 8866, were infected with the Edmonston strain of measles virus at a multiplicity of infection of 10(-6), and stable persistent infections were established. By immunofluorescence and electron microscopy, the vast majority of cells from both cell lines were expressing viral antigens and releasing virion-like particles. However, very little infectious virus could be detected at 37 degrees C, either by an infectious centers assay or by titration of supernates from persistently infected cultures. When cultures were shifted to 31 degrees C, the cells released a population of virus that was temperature-sensitive. Clonal analysis of supernatant virus at 31 degrees C revealed a highly heterogeneous population of temperature-sensitive mutants, differing in plating efficiency ratios, thermolability, and antigen production at the nonpermissive temperature. Factors such as interferon, defective interfering particles, and extracellular virus do not appear to be important in maintaining the persistent carrier state. These studies have important implications for persistent infections of lymphoid cells in vivo, and the slow neurological diseases associated with measles, subacute sclerosing panencephalitis, and multiple sclerosis.

Mechanism of rejection of virus persistently infected tumor cells by athymic nude mice.

Cell lines known to be tumorigenic in the nude mouse were modified by rendering them persistently infected (P.I.) with a variety of RNA viruses, including measles, mumps, vesicular stomatitis virus, and influenza. Although as few as 100 HeLa or BHK cells produced tumors in 100% of nude mice, as many as 2 x 10(7) of the same cells P.I. with viruses failed to produce tumors. An active host response responsible for restricting the growth of the P.I. cells was suggested by the findings of marked mononuclear cell infiltrates at the inoculation sites and the inability of irradiated nude mice to reject them. An analysis of the in vitro cytotoxic activity of spleen cells from normal nude mice indicated that: (a) P.I. cell lines, but not uninfected cell lines, were susceptible to spontaneous cytotoxicity; (b) in vivo inoculation of P.I. lines induced an enhanced cytotoxic activity for P.I. targets in vitro, and this induction was not specific either for inducing virus or cell line; and (c) the effector cell had the characteristics for natural killer (NK) cells. Although the specificity of recognition of the various P.I. cell lines remains unclear, cold competition experiments indicated that blocking the killing of one P.I. cell line, e.g. HeLa-measles, could be achieved only by unlabeled homologous cells, i.e. HeLa-measles, and not by uninfected cells or other P.I. lines. A variant subline of BHK cells P.I. with VSV was selected for its ability to withstand the rejection process in nude mice. These cells formed metastatic and invasive tumors in nude mice. Although they were the most potent inducers in vivo of NK cell activity against various P.I. targets, they were the most resistant of the P.I. lines to NK cell cytotoxicity in vitro. In this system there was a good correlation between tumor rejection in vivo and susceptibility to NK cells in vitro. The present results suggest that NK cells may play a significant role in both rejection of tumor cells, and in resistance to viruses, particularly persistent infections.

Interferon as a mediator of human lymphocyte suppression.

Evidence is presented that interferon (IF) is a major mediator of the human concanavalin A (Con A) suppressor cell. The suppressive effects of Con A-activated lymphocytes on the mitogen responses of normal responder cells were largely abrogated by addition of anti-human leukocyte IF serum. Similar suppressor activity was generated by coculture of peripheral blood leukocytes (PBL) with a melanoma cell line (MeWo) and a HeLa cell line persistently infected with measles virus that induced the production of IF by lymphocytes. A human mammary carcinoma line (MCF-7) and two bladder carcinoma lines (T24 and TCCSUP) failed to induce IF or suppression. Addition of anti-human leukocyte IF serum to suppressor cells and supernates from tumor cell-lymphocyte cocultures largely abolished suppression and neutralized the antiviral activity of such supernates. Exposure of PBL from purified protein derivative (PPD)-positive donors to PPD caused the production of suppressor activity and IF. PBL from PPD-negative donors failed to produce significant amounts of IF or to suppress on exposure to PPD. Supernates from PBL treated with virus (Newcastle disease virus [NDV]) contained IF and suppressed the mitogen responses of responder PBL. Both the suppressive and the antiviral activities of this material were eliminated after treatment with anti-IF serum. To ascertain whether antiviral and suppressive activities were mediated by the same types of IF, supernates from PBL cultured with Con A, PPD, NDV, and tumor cells were treated with anti-IF serum or acid pH. In all cases antiviral activity was neutralized in parallel with abrogation of suppressor activity. These results provide strong evidence for the role of IF as a mediator of human suppressor cell activity.

Macrophage variants in oxygen metabolism.

Whereas phagocytic cells from normal individuals have the capacity to kill ingested bacteria and parasites, those from patients with several uncommon genetic deficiency diseases are known to be defective in bactericidal activity. Studies on neutrophils of these patients have revealed fundamental defects in their ability to reduce molecular oxygen and metabolize it to superoxide anion, hydrogen peroxide, and oxygen radicals. In the present experiments, we describe a clone of a continuous murine macrophage-like cell line, J774.16, that, upon appropriate stimulation, activates the hexose monophosphate shunt, and produces superoxide anion and hydrogen peroxide. With nitroblue tetrazolium to select against cells capable of being stimulated by phorbol myristate acetate to reduce the dye to polymer--formazan--which is toxic fot cells, we have selected for variants that are defective in oxygen metabolism. Four of these subclones have been characterized and found to be lacking in the ability (a) to generate superoxide anion, as measured by cytochrome c reduction; (b) to produce hydrogen peroxide, as measured by the ability to form complex I with cytochrome c peroxidase; and (c) to be stimulated to oxidize glucose via the hexose monophosphate shunt. These variants appear to represent a useful model for studying the molecular basis for macrophage cytocidal activity.