Mechanisms of genetic resistance to Friend virus leukemia. III. Susceptibility of mitogen-responsive lymphocytes mediated by T cells

The Accidental Pathologist: A Curiosity-Driven Journey from Plant Evolution to Innate Immunity

I have had the singular opportunity to perform research and to participate in medical education. Not unexpectedly, people have asked me which of the two was more important to me. My answer has always been and remains that I am equally passionate about research and teaching. My research has been curiosity driven and not purposeful; hence, I was willing to take risks. That my research led to the discovery of natural killer cells and the unraveling of the molecular basis of a human disease was an unexpected reward. By contrast, my interest in medical education was purposeful, with the goal of improving healthcare by teaching pathology as the scientific foundation of medicine. It started with participation in Robbins pathology texts but progressed toward development of technology-based tools for medical education. This was driven by the belief that technology, by providing equal access to knowledge across the world, can be a powerful democratizing force.

Effect of Friend leukemia virus infection on susceptibility to Candida albicans

Previous studies have demonstrated that Friend leukemia virus (FLV) induces a profound immunosuppression in susceptible mice. The studies described in this report indicate that mice infected with FLV have an increased susceptibility to subsequent infection with the opportunistic pathogen Candida albicans, as measured by increased numbers of C. albicans CFU in the kidneys of FLV-infected mice relative to uninfected controls. Experiments in which the NB-tropic and N-tropic strains of FLV were used suggest that virus replication or the resulting virus burden may be important in the observed increased susceptibility to C. albicans. Since neutrophils are believed to be important in the response of mice to systemic Candida infections, the effect of FLV infection on neutrophil candidacidal activity was investigated. The percentage of neutrophils present in unfractionated Proteose Peptone-elicited peritoneal exudates of mice infected with FLV for 14 days was significantly lower than in uninfected control mice or mice infected with FLV for 6 or 10 days. When neutrophils from FLV-infected and control mice were purified, adjusted to equal concentrations, and tested for in vitro candidacidal activity, neutrophils from mice infected with FLV for 14 days were deficient in their ability to kill C. albicans relative to normal controls and mice infected with FLV for 6 or 10 days. Addition of normal mouse serum increased killing in all groups but did not restore candidacidal activity of neutrophils from mice infected with FLV for 14 days to levels of control neutrophils or neutrophils from mice infected for 6 or 10 days with the virus. These results suggest a defect in neutrophil function, at the later stages of FLV infection, involving in vitro candidacidal activity. In addition, neutrophils from FLV-infected mice may be deficient in in vivo chemotactic activity. These defects in neutrophil function could account, at least in part, for the observed increased susceptibility of FLV-infected mice to C. albicans.

Influence of the murine MHC (H-2) on Friend leukemia virus-induced immunosuppression

Friend murine leukemia virus complex (FV)-induced immunosuppression was studied by assaying splenic anti-SRBC PFC responses and plasma antibody titers in mice at various times after FV inoculation. Genes located within the H-2 complex were found to influence resistance to FV-induced immunosuppression. Near normal responses were observed in mice having the H-2a/b or H-2b/b genotype, whereas mice having the H-2a/a genotype were suppressed. This H-2 effect was observed not only in mice having heterozygous C57BL/10 X A background genes, including Rfv-3r/s, but also was apparent in mice having homozygous A-strain background genes, including Rfv-3s/s. Therefore, the Rfv-3 gene did not appear to convey resistance to FV-induced immunosuppression. The suppression in susceptible H-2a/a mice was characterized by a partial suppression of the IgM response and a profound suppression of both the primary and secondary IgG responses. Neither splenomegaly nor viremia alone appeared to be sufficient for the induction or maintenance of the immunosuppression. The mechanism of suppression was unclear, but both B lymphocyte and T lymphocyte functions appeared to be altered.

Target cell heterogeneity in murine leukemia virus infection. III. Identification of susceptible Lyt 1+ and resistant Lyt 2+ T-cell subsets following in vitro infection with Friend murine leukemia virus

The susceptibility of splenic T-cell subpopulations to productive infection with Friend murine leukemia virus was determined after in vitro infection and stimulation with Con A. Con A enhanced the number of productively infected cells in unseparated spleen cells as well as in T-cell-enriched spleen cell fractions. Splenic T cells were fractionated into Lyt 1+ and Lyt 2+ subpopulations using both positive and negative selection techniques; susceptible splenic T cells were recovered in the Lyt 1+ fraction and specific cytotoxic treatment with anti-Lyt 1 antibody and complement reduced the number of infectious center-producing cells by greater than 87%. In marked contrast, Lyt 2+ splenic T cells were resistant to productive infection by Friend murine leukemia virus in vitro.

Contrasuppression: the second law of thymodynamics, revisited

The data discussed here touch upon several issues in the evolving story of T cell contrasuppression, the underlying theme being that of heterogeneity. First, there is the issue of function. We are considering here only those cells that affect the function of secretory differentiation. We have evidence that different contrasuppressor cells exist for clone growth, but have not yet studied them in the same depth as those for secretory differentiation. Second, there is the important issue of target cells. In this article by Green and Gershon it is pointed out that there is clear evidence that contrasuppressor effects can work by protecting helper cells from suppressor cell effects in vitro. On the other hand, direct additional inhibition of the suppressor cells themselves has not been excluded. The latter point is also true in our system. However, we must suppose for the sake of simplicity in many of our experiments that if suppressors are not the target of the contrasuppressor effects then the B cells themselves probably are. This is because the tumor cells engage in a spontaneous rate of growth and differentiation in the absence of help or suppression. When T cell-dependent, specifically triggered effects reduce this spontaneous behavior, then a suppressive effect must have been delivered directly to the B cells. This is a simplifying assumption which is attractive, but since the experiments are carried out in vivo and thus may be affected by some factors that we have not yet recognized, we are not confident on its "intuitive" appeal. A third issue revolves around triggering specificity. One of our contrasuppressors exhibits the phenomenon of carrier crossreactivity (CRCS) and is thus behaving in accord with expectations aroused by Green and Gershon in this review. The other cell is apparently quite carrier specific (SCS). The meaning of this is not at all clear, but its potential significance may somehow be related to a sort of "mirror image" relationship of the two cells. Thus, for example, in other experiments not discussed here, we have noted that the CRCS binds to 315 protein-coated plates, but as noted here counteracts a suppressive effect which is generated by cells which do not adhere to these plates. In contrast to SCS does not bind to 315 plates and yet, as noted here, appears to counteract a suppressor effect generated by cells which do adhere to 315 plates.(ABSTRACT TRUNCATED AT 400 WORDS)

T and B lymphocyte susceptibility to murine leukemia virus moloney

The susceptibility of T and B lymphocytes to productive infection and transformation by murine leukemia virus Moloney was determined by enumeration of cells producing infectious virus after in vitro infection of mitogen-stimulated, isolated cell populations and by in vivo infection of euthymic BALB/c and thymus-deficient (nude) mice. Our in vitro results demonstrated that the majority of splenic T cells and thymocytes are resistant to productive infection in vitro; a specific subpopulation of susceptible nylon-adherent splenic T cells was identified, however. Similarly, surface immunoglobulin-positive B cells also represent susceptible targets in vitro; mature B cells, however, did not represent the principal target for transformation in the in vivo experiments. Infected euthymic mice expressed increasing titers of murine leukemia virus and uniformly developed fatal T-cell lymphomas at 10 to 12 weeks postinfection; nude mice, in contrast, maintained high, stable levels of viremia throughout the 28 weeks of observation. Infected nude mice remained free of malignancy or developed either granulocytic leukemias or, in one case, reticulum cell sarcoma. Collectively, the results indicate that while the majority of T cells are resistant to productive infection, they represent the principle targets for transformation; B cells, however, represent permissive targets for virus replication, but are resistant to transformation.

H-2D control of recovery from Friend virus leukemia: H-2D region influences the kinetics of the T lymphocyte response to Friend virus

A Friend virus (FV)-specific T lymphocyte proliferation assay was used to compare the T lymphocyte responses of H-2 congenic mice that differed in their ability to recover from FV leukemia after inoculation of high virus doses. Gene(s) of the H-2D region influenced the kinetics of this response such that H-2Db/b homozygous mice were positive 6-8 d earlier than H-2Dd/b mice. This correlated with the Rfv-1, H-2D-linked influence on recovery from FV by these mice, and also appeared to explain the prominent effect of virus dose on recovery incidence. These findings were supported by the ability of passively transferred immune splenic T lymphocytes to induce recovery from leukemia at 6 d after FV inoculation, but not at 16 d. H-2a/a mice were found to be unresponsive in the FV-specific T lymphocyte proliferation assay. This effect mapped to the left of H-2D, possibly in the H-2I region, and may be an in vitro manifestation of the Rfv-2 gene. No evidence for nonspecific immunosuppression of the T lymphocyte response to concanavalin A was observed in any of the H-2 congenic F1 mice studied.

Aging of natural and acquired immunity of mice. II. Decreased T cell responses to syngeneic tumor cells and parental-strain spleen cells

Cytolytic T lymphocyte (CTL) functions were compared in mice between the ages of 2 and 30 months. The stimulator cells were H-2 allogeneic spleen or tumor cells, parental-strain spleen cells, or syngeneic tumor cells. Effector cells capable of lysing syngeneic tumor cells were shown to be T cells and not NK cells. The cell-mediated lympholysis (CML) responses by spleen cells of aged mice were near normal against H-2 allogeneic spleen or tumor cells but were defective against syngeneic tumor cells or parental-strain spleen cells. The defective syngeneic tumor CML response was observed at various responder:stimulator ratios and at various days of incubation. The defect was in the nonadherent, and not in the adherent, fraction of spleen cells. Suppressor cells were detected in spleens of 30 month, but not of 18 month old mice. Aged mice were more susceptible than young mice to small inocula of syngeneic C57BL EL-4 lymphoma cells. The immunogenicity of irradiated spleen cells of old mice had not changed for the F1 antiparent CML response. Splenic CML responses of young mice treated with 89Sr demonstrated a similar pattern, i.e., good responses to H-2 allogeneic stimulator cells but poor responses to syngeneic tumor cells or to parental-strain spleen cells. This loss of certain CTL functions influenced by marrow dependent cells can partially explain the increased susceptibility of old animals to tumors.

Aging of natural and acquired immunity of mice. I. Decreased natural killer cell function and hybrid resistance

Two "natural resistance" functions, natural killer (NK) cell activity against YAC-1 lymphoma cells and rejection by irradiated mice of parental-strain or H-2 allogeneic bone marrow cell grafts (hybrid or allogeneic resistance) were compared in mice at ages between 10 weeks and 26 months. NK cell numbers, as assessed by target-binding cells, decreased to one-half that of young mouse spleen cells, whereas NK lytic function was much more depressed. Hybrid, but not allogeneic, resistance to marrow grafts was weakened by 17 months of age. The immunogenicity of marrow stem cells of old Fl hybrid mice had not changed. The interferon inducer polyinosinic:polycytidylic acid (pI:pC) restored hybrid resistance to marrow grafts but only weakly boosted NK cell function in old mice. Incubation of spleen cells of old mice with beta interferon resulted in a weak boosting of NK cell activity. No cells capable of inhibiting NK cell function were detected in the spleens of old mice. These findings in old mice were similar to findings in young mice treated with 89Sr, with the exceptions that both hybrid and allogeneic resistance to marrow grafts are defective in 89Sr-treated mice and pI:pC failed to restore hybrid resistance in mice treated with 89Sr. This loss of "natural resistance" by aged mice, perhaps mediated by marrow-dependent effector cells, can partially explain the increased incidence of tumors in aging populations.

Immunotherapy of murine leukemia. VII. Prevention of Friend leukemia virus-induced immunosuppression by passive serum therapy

Previous studies have suggested that the passive therapy of Friend leukemia virus (FLV)-induced disease with chimpanzee anti-FLV serum operates by reducing the level of infectious virus in the treated animal below the immunosuppressive threshold, thereby allowing the host to mount anti-viral immune responses which are responsible for long-term protection. The present study was undertaken to examine directly the effect of passive serum therapy on the marked immunosuppression induced by FLV in progressively infected mice, as well as to determine whether virus-specific host cellular immune effector functions are augmented in serum-protected animals. Using a variety of assays of host immunocompetence, including natural killing (NK), antibody-dependent cellular cytotoxicity (ADCC) in vivo and in vitro induction of allogeneic killers, and mitogen blastogenesis, a marked compartmentalization of FLV immunodepression was observed in progressively infected DBA/2 mice, possibly reflecting the distribution of FLV target cells in various host lymphoid populations. Thus, spleen-cell functions were suppressed most rapidly and to the greatest degree, followed by peritoneal cells and peripheral blood lymphocytes, while lymph node cells and thymocytes maintained normal levels of activity. In contrast, serum-protected mice demonstrated no sign of FLV-induced immunosuppression regardless of the host effector-cell population or immune function examined. However, we were not able to identify host anti-viral cellular immune functions which are significantly enhanced in serum-protected animals; thus the specific role of the host immune system in the passive serum therapy of FLV-induced disease remains undefined at the present time.

Analysis of low natural killer cell activity in 89Sr-treated mice

Treatment of mice with the long-lived bone-seeking radioisotope 89Sr results in the selective irradiation and destruction of the bone marrow. This is accompanied by a marked reduction in natural killer cell activity against YAC-1 lymphoma [NK(YAC-1)]. To test for the presence of cellular suppressors of NK(YAC-1) in 89Sr-treated mice, in vitro and in vivo cell mixture protocols were used. In vitro, we did not observe any specific inhibitory effect of spleen cells from 89Sr-treated mice on NK(YAC-1) activity of normal spleen cells. The NK(YAC-1) activity of 89Sr-treated mice, measured in vivo by their ability to clear radiolabeled YAC-1 cells from the lungs, was impaired. However, spleen cells from 89Sr-treated mice, when adoptively transferred with normal spleen cells, failed to inhibit the NK(YAC-1) activity of the latter in the lung clearance assay. Further, when normal spleen cells were injected into 89Sr-treated mice, the ability of the transferred cells to mediate in vivo activity was not suppressed in the 89Sr-treated host. These experiments support the suggestion that the low NK(YAC-1) activity in 89Sr-treated mice is not mediated by suppressor cells, but may be due to the destruction of the marrow microenvironment which is essential for the generation of functional NK(YAC-1) cells.

Murine cytomegalovirus stimulates natural killer cell function but kills genetically resistant mice treated with radioactive strontium

Treatment of C3H/St mice with 100 microCi of 89Sr weakened their genetic resistance to murine cytomegalovirus (MCMV) infection. The criteria utilized to detect increased susceptibility were: (i) survival of mice; (ii) numbers of MCMV-infected cells in the spleens and liver; and (iii) serum glutamic pyruvic transaminase levels. The natural killer (NK) cell activity of spleen cells from mice treated with 89Sr is very low. However, the NK activities of spleen cells of both normal and 89Sr-treated mice were greatly augmented 3 days after infection with MCMV. These NK cells lysed a variety of tumor cells and shared several features with conventional NK cells, but were not lysed by anti-Nk-1.2 serum (specific for NK cells) plus complement. Splenic adherent cells did not lyse tumor cells themselves but were necessary for the stimulation of NK cells by MCMV. The paradox of high NK cell function and poor survival in 89Sr-treated mice infected with MCMV was a surprise. We conclude that these augmented NK cells, of themselves, cannot account for the genetic resistance of C3H/St mice to infection with MCMV.

Impairment of in vitro generation of cytotoxic or T suppressor lymphocytes by Friend leukemia virus infection in mice

Spleen cells collected from DBA/2 (H-2d) mice inoculated with the polycythemic variant of Friend-Leukemia Virus Complex (FLV-P) were tested for T-dependent immune functions, such as the in vitro generation of cytotoxic T lymphocytes (CTL) and of non-specific T suppressor lymphocytes (STL). CTL were generated against H-2b splenocytes, and STL were obtained following a 5-day lymphocyte culture without stimulator cells. A progressive and severe impairment of the generation of both CLT and STL was found from 2 weeks onward after infection, being almost totally abolished 3-4 weeks after virus challenge. Suppressor cells (SC) capable of inhibiting CTL generation was detected in FLV-P bearing mice. Suppressor activity was unaffected by anti-Thy 1.2 serum and complement but was removed following iron-magnet depletion or passage through nylon-wool column. Moreover complete recovery of the competence of CTL generation was attained when FLV-P infected splenocytes were passed through nylon-wool column. It is concluded that FLV-P infection depresses T-dependent cytotoxic and suppressor responses in mice, by the appearance of non-T adherent phagocytic cells, capable of impairing CTL generation in vitro.

Hybrid resistance to EL-4 lymphoma cells. II. Association between loss of hybrid resistance and detection of suppressor cells after treatment of mice with 89Sr

(C57BL/6 X DBA/2)F1 hybrid (B6D2F1) mice resist the growth of parental-strain (B6) EL-4 lymphoma cells inoculated intraperitoneally; that is, B6D2F1 mice survive longer than B6 mice and do not develop ascites. As compared with B6 mice, B6D2F1 mice have higher levels of natural killer (NK) activity against 51Cr-labelled EL-4 cells in their lymphoid organs. B6D2F1 mice treated with 89Sr lose NK activity for certain lymphoma cell targets, e.g. YAC-1, but NK(EL-4) function is usually intact. However, 89Sr-treated mice had lost hybrid resistance to EL-4 cells in vivo, as determined by survival by irradiated or unirradiated EL-4 cells, Corynebacterium parvum, or polyinosinic:polycytidylic acid (pI:pC) in spleens of normal B6D2F1 mice, but NK(EL-4) activity was depressed within 3 days by such treatment in B6D2F1 mice previously injected with 89Sr. Suppressor cells for NK(EL-4) but not for NK(YAC-1) effectors were easily detected in spleens of 89Sr-treated mice "challenged' with C. parvum. Thus, agents capable of stimulating NK cell function in normal mice may lead to suppression of that activity in mice depleted of marrow-dependent cell function by 89Sr. Spleen cells of 89Sr-treated B6D2F1 mice were also unable to generate anti-EL-4 cytotoxic T lymphocytes in a cell-mediated lympholysis system; this defect appeared also to be mediated by suppressor cells. Lymphoid cells depleted by 89Sr-induced marrow aplasia may have two functions in host defences against tumours (especially lymphomas): they may lyse tumour cells directly and they may "down-regulate' suppressor cells capable of inhibiting other "natural' or "induced' immune functions.

Target cell heterogeneity in murine leukemia virus infection. II. Demonstration of Friend leukemia-virus-permissive and non-permissive subsets of splenic T cells

The permissiveness of normal splenic lymphocytes to Friend murine leukemia virus was determined by enumeration of cells producing infectious MuLV following infection with Friend virus in vitro. The infection was enhanced greatly in the presence of mitogens in the culture medium. The number of infected cells in cultures stimulated with bacterial lipopolysaccharide increased progressively between days 1 and 7 whereas in cultures with concavalin A, the number of infected cells reached a maximum on days 3-4 post infection and then declined to the level observed in unstimulated cultures. The con-A-enhanced infection was absent in cultures of splenocytes from nude mice but was present in cultures from nude mice implanted with thymus glands 6 weeks or more before use as donors of spleen cells. The cells permissive to MuLV upon con-A stimulation segregated in the nylon-wool-adherent fraction (together with B cells involved in the LPS-dependent infection) whereas the nylon-non-adherent fraction, containing approximately 90% T cells, was refractory to in vitro infection. The con-A-dependent infectious centers were inhibited by cytotoxic treatment with anti-Thy 1.2 antibody plus complement. These results indicate the existence of two subpopulations of splenic T cells, a major nylon-non-adherent and a minor, nylon-adherent subpopulation, which are, respectively, non-permissive and permissive to MuLV-Friend.

H-2D (Rfv-1) gene influence on recovery from Friend virus leukemia is mediated by nonleukemic cells of the spleen and bone marrow

H-2D (Rfv-1)-associated control of recovery from FV leukemia was studied in congenic mice. In irradiation chimeras, the high recovery phenotype was transferred by cells of the spleen, bone marrow, and fetal liver. Furthermore, in cell transfers using unirradiated recipients, spleen and bone marrow cells of the high-recovery genotype were able to mediate recovery from leukemia in mice of the low-recovery genotype. Thus, the H-2D (Rfv-1) influence on recovery appeared to operate via nonleukemic cells of the spleen and bone marrow rather than via leukemic cells. The specific nonleukemic cell type(s) involved in recovery remains unknown. However, the mechanism appears to be complex and probably involves both anti-FV antibody and FV-specific cytotoxic T lymphocytes.

H-2 associated resistance to leukaemia transplantation: natural killing in vivo

Natural resistance in vivo was studied by injecting non-immunized mice with leukaemia cells prelabelled with the thymidine analogue 131I-iododeoxyuridine. There was a decrease in the survival of the leukaemia cell inoculum as determined by whole-body gamma counting, and a failure of the leukaemia cells to survive in the spleens of mice which were not H-2 identical with the transplant. H-2-associated resistance could be measured within 24 h of leukemia inoculation and was strongest in the spleen and absent from the liver. Although all strains of mice tested were able to resist H-2 non-identical cells, resistance in irradiated (800--900 R) mice was restricted to certain strains and their F1 hybrids, notably those of the C57BL family. Resistance in both non-irradiated and irradiated mice was not due to classical immunological rejection. Mice with either genetic or induced T-cell deficiency showed full resistance, and circulating preformed antibody could not account for the rejection observed. Treatment with silica or with 89Sr abrogated natural resistance in non-irradiated as well as irradiated animals; these treatments had previously been shown to abolish both bone-marrow graft rejection in irradiated mice and in vitro natural killing. Resistance against leukaemia transplantation in irradiated C57BL mice appeared to depend on Hh-1 (H-2D) incompatibility between the host and the graft, again suggesting that bone-marrow graft rejection, and perhaps natural killer activity, is a subset of a more general paraimmune or non-adaptive rejection mechanism.

Hybrid resistance to EL-4 lymphoma cells. I. Characterization of natural killer cells that lyse EL-4 cells and their distinction from marrow-dependent natural killer cells

Natural killer (NK) cells from nonimmunized mice capable of lysing EL-4 (C57BL/6 strain H-2b) tissue culture-adapted lymphoma cells have been analyzed and compared with NK cells which lyse YAC-1 (A-strain, H-2a) lymphoma cells. A correlation was seen in the ability of inbred and B6D2F1 mice to reject C57BL/6 (B6) bone-marrow grafts and the ability of their spleen cells to lyse EL-4 cells in vitro. This suggests that hybrid or hemopoietic histocompatibility antigens, (Hh-1b), relevant in the rejection of B6 stem cells may also be the relevant target structures for the anti-EL-4 NK cells. Certain features of these NK cells are similar to the NK cells reactive against YAC-1 cells. Both types of NK cells are present in athymic nude mice, are not affected by treatment with anti-immunoglobulin plus complement, and are not depleted by techniques that remove macrophages. NK activity against both targets is stimulated 3 d after injection of Corynebacterium parvum, and 24 h after challenge with polyinosinic:polycytidylic acid. Hydrocortisone acetate and cyclophosphamide lead to reduction of NK activity within 2-3 d after administration. However, the anti-YAC and anti-EL-4 NK reactivities differed in several important respects. Treatment of mice with 89Sr, the bone-seeking isotope, to deplete marrow-dependent cells, depleted the anti-YAC-1 but not anti-EL-4 cell functions. Anti-EL-4 NK cells were unaffected by silica particles in vivo or in vitro; the NK cells reactive to EL-4 cells matured functionally much earlier in life (5 d of age) and the function did not decline with age. Irradiated mice reconstituted with syngeneic marrow or spleen cells developed functional NK cells against EL-4 targets before they developed anti-YAC-1 NK cells in their spleen. Thus anti-EL-4 NK cells that express hybrid resistance in vitro appear to differ from anti-YAC-1 NK cells and do not require an intact marrow microenvironment for functional differentiation. Despite differences in the NK-cell types involved in the lysis of YAC-1 and EL-4 cells, these two tumor cells share certain common determinants. This was ascertained both by cold competition and by utilization of YAC-1 and EL-4 cell monolayers as immunoadsorbents. We conclude that Hh-1b is the common antigen present in EL-4 and YAC-1 cells, because B6D2F1 anti-B6 (anti-Hh-1b) cytotoxic T lymphocytes lysed both the tumor cells. Our data suggest that Hh-1b antigen is recognized by both types of NK cells, but that additional determinants must be present on YAC-1 cells. Two models of NK cell lysis compatible with the data are presented.

Immunosuppression by Friend leukemia virus is H-2 restricted by alloreactive T lymphocytes

Friend leukemia virus suppresses mitogen-responsive cells in vitro by activating thymus-dependent suppressor cells. The interaction between T suppressor and mitogen-responsive cells is H-2D restricted by a third cell type, called an interfering cell. The interfering cells could be characterized as alloreactive T cells that functionally mature in the spleen at 2 weeks of age and that can be functionally inhibited by mitomycin C, irradiation, and cortisol. Interfering cells are stimulated by H-2D (and not H-2L) alloantigens of the mitogen-responsive cells. H-2D differences between interfering and T suppressor cells are unimportant. Induction of "tolerance" to H-2 alloantigens in semi-allogeneic radiation marrow chimeras resulted in the specific loss of interfering cell function. It is possible that interfering or similar cells participate in other forms of H-2 restriction.

Immune depression in trypanosome-infected mice. III. suppressor cells

Spleen cells from trypanosome-infected mice strongly suppressed lymphocyte stimulation induced in normal spleen cell populations by lipopolysaccharide, concanavalin A or allogeneic (H-2-different) stimulator cells. This suppression was not H-2-restricted, as responses of spleen lymphocytes both allogeneic and syngeneic to the suppressors were inhibited. Irradiation or mitomycin C treatment of suppressor populations markedly reduced but did not eliminate suppressor activity. Suppressor populations were effective when present in very low numbers. Addition of suppressor cells to mixed lymphocyte cultures at various intervals after initiation of the cultures showed that the suppressors require 48 h to manifest their activity. Cell depletion or enrichment experiments indicate that the mechanism of suppression is complex and involves more than one cell type.

Persistence and pathogenicity of defective Friend spleen focus-forming virus. Decreased transplantability of hemopoietic cells as a marker for preleukemic change

A latent form of persistent infection can be established in susceptible adult mice inoculated with a preparation of defective Friend spleen focus-forming virus (SFFV) purified free from standard leukemia-inducing helper virus (LLV-F). SFFV persistence was initially observed using an in vivo rescue technique in which SFFV could be directly rescued to form splenic foci of malignant erythropoiesis in mice. At approximately 30 d after virus inoculation however, SFFV could not be rescued after inoculation of LLV-F indicating that persistently infected (i.e., SFFV+) mice were either immume to exogenous helper virus or able to express SFFV-associated defective-interfering (DI) function(s). Persistent infection by SFFV was further documented using an in vitro rescue technique and ultimately resulted in the induction by SFFV of erythroleukemia in the absence of polycythemia or overt virus production. However, SFFV rescued by LLV-F from persistently infected normal and transformed hemopoietic cells was able to induce polycythemia in adult mice suggesting that this is a helper controlled property of the Friend virus complex. Transplantable SFFV-induced erythroleukemic cells could be retrieved from persistently infected yet histologically normal mice. The duration of SFFV persistence in normal spleen tissue suggests that the SFFV provirus resides in either a long-lived or pluripotent hemopoietic cell. Further, certain changes occurred, presumably in the membranes of persistently infected cells, which preceded the overt development of Friend leukemia and facilitated the definition of an SFFV preleukemic phase. Cell surface alterations were revealed using cell transfer techniques. Hemopoietic cells harboring a rescuable SFFV failed to proliferate when inoculated into lethally irradiated, syngeneic adult mice. In contrast, the transformed progeny of preleukemic cell populations and spleen cells transformed by FV complex (i.e., cells replicating both SFFV and LLV-F) were not rejected. This result suggests that histologically normal SFFV+ preleukemic cells express an antigen recognition site which is not present on overtly transformed cells and which may be a pertinent surveillance target for host anti-leukemogenic reactions.

Casein-induced experimental amyloidosis. IX. Alterations in marrow dependent function

CBA/J mice receiving multiple injections of sodium caseinate (CAS) or bovine serum albumin (BSA) were assayed for marrow dependent functions by measuring their ability (i) to reject bone marrow allografts and (ii) to resist Friend virus (FV)-induced suppression of lymphocyte mitogenesis. Mice that developed amyloidosis following 25-30 injections completely lost the ability to reject allogeneic marrow cells, whereas nonamyloid BSA-treated mice had enhanced rejection of marrow allografts. There was increased resistance to the suppressive effects of FV in spleen cells from 'preamyloid' mice receiving CAS injections and nonamyloid mice receiving 10-40 BSA injections. Amyloid mice appeared to be as susceptible to the effects of FV-induced suppression as control (untreated) animals. These data indicate that alterations in marrow dependent function may be related to the pathogenesis of amyloid disease.

The immunodepressive effect of Friend virus. IV. Effects on spleen B lymphocytes

Splenic immune responses having varying dependence on accessory cell co-operation have been studied after infection of mice with Friend virus. Infection has no effect on cell proliferation or antibody production in cultures stimulated with E. coli lipopolysaccharide. The response in vivo to type III pneumococcal polysaccharide is depressed only moderately. The response to sheep red blood cells is depressed severely both in vivo and in vitro. Depression in vitro is greatly reduced by co-stimulation with E. coli lipopolysaccharide. Depletion of potential suppressor lymphocyte populations by irradiation or adult thymectomy does not ameliorate depression of responses to sheep red blood cells or pneumococcal polysaccharide. Responses after adult thymectomy plus irradiation are not affected by the virus. Although it is known that macrophage and helper T-lymphocyte co-operation are not themselves impaired by infection, these results suggest that there is a direct relationship between severity of immune depression and dependence on co-operation. Implications for the action of the virus are discussed.

Mechanisms of genetic resistance to Friend virus leukemia in mice. IV. Identification of a gene (Fv-3) regulating immunosuppression in vitro, and its distinction from Fv-2 and genes regulating marrow allograft reactivity

Friend leukemia viru (FV) suppresses the proliferative response of normal lymphocytes to mitogens. The in vitro suppressive effect of FV on lymphocyte mitogenesis is mediated by T-suppressor cells and is under host genetic control. Lymphocytes from strains of mice of the C57BL background (e.g., C57BL/6) are resistant while cells from other strains (e.g., 129 and DBA/2) are susceptible. Genetic analyses utilizing resistant and susceptible parental strains, their F1, intercross and backcross progeny indicated that susceptibility to in vitro suppression is regulated by a single autosomal gene, dominant for susceptibility to suppression. This gene, which is not linked to the H-2 complex, segregated independently of the Fv-2 gene which controls resistance to spleen focus formation in vivo. The gene is also unlinked to the Ir-like genes which regulate the ability of H-2d mice to reject H-2b bone marrow grafts. The gene is therefore designated as Fv-3. Fv-3 may mediate its effect by regulating the numbers and/or functions of T-suppressor cells.

Genetics of resistance of animals to viruses: I. Introduction and studies in mice

Inherited resistance to animal viruses may be conveniently classified into three types: monogenetic, following simple mendelian ratios; polygenetic; and cytoplasmic. A virus is a unique cellular parasite, dependent upon the host for reproduction and nourishment in a variety of different ways. Since, as with the other types of parasites, the host and the parasite have necessarily evolved together. It is a distortion to consider the resistance of the host, without considering the evolutionary steps in the development of this extreme form of parasitism; therefore, this chapter reviews some of the ideas put forward about host-agent interactions in plants as well as in animals. The importance of genes in regulating the resistance to disease, including parasites and parasitoids, is apparent if the disease is considered to be an important evolutionary force. The selective effects of viruses have not yet been adequately studied. Continued attempts to find a correlation between the different blood groups and differing severity of smallpox infection clearly searched for selective forces, but the results were inconclusive. Most of the knowledge of genetic resistance to virus disease rests on the study of resistance to selected agents in various inbred strains of mice and chickens, rather than on any knowledge of the effects of genetic resistance in a natural heterozygous population. The increasing frequency, however, with which genetic resistance is found, is in itself an evidence that these genes are important in natural outbred populations. In addition, there are increasing numbers of virus diseases, in which the viral agent seems to be inherited in a mendelian fashion.

Direct cytotoxicity against chicken erythrocytes in mice. I. Fundamental nature of T cell-mediated cytotoxicity

Immune responses were examined after immunization with chicken erythrocytes (CRBC) in mice. Cytotoxicity of spleen cells was assessed by the release of 51Cr from labelled target cells. (1) At early stages (day 4-7) after primary intraperitoneal immunization, direct cytotoxicity of spleen cells was raised efficiently in C57BL/6 and AKR mice, but not in C3H/He, SL and DDD mice. Delayed hypersensitivity and antibody production were raised to almost the same extent in all the strains at such periods. (2) Effector cells in direct cytotoxicity were theta-positive and IgG-positive, and glass-nonadherent and Nylon wool column-adherent. Effector cells in antibody-dependent cell-mediated cytotoxicity in the presence of antibody to CRBC were eliminated by treatment with anti-IgG serum, but not by treatment with anti-theta serum. (3) Cytotoxicity and antibody production were raised efficiently after intraperitoneal or intravenous immunization, but not after footpad immunization. On the other hand, delayed hypersensitivity developed most efficiently after footpad immunization.

The immunodepressive effect of Friend virus III. Effects on spleen T cells

We have examined various T lymphocyte functions in the spleens of mice infected 4 days previously with Friend viurs (FV) in order to analyse its effect on the antibody response. We have found (a) that infection does not reduce the percentage of T lymphocytes in the spleen, nor their ability to respond to PHA, (b) that infected spleen cells mediate allogeneic augmentation of the primary response to SRBC in vitro, even though their own depressed response cannot be restored via the allogeneic effect, and (c) that infected spleen cells restore responses to SRBC by both allogeneic and syngeneic spleen cell cultures depleted of T lymphocytes. These results suggest that FV does not affect spleen T lymphocyte proliferation of helper function. Since macrophages from infected spleens cooperate normally in the response to SRBC in vitro, we conclude that the immune defect resides in the B lymphocytes.

Nephrotic syndrome of childhood and disorder of T cell function

In thirty-two patients with nephrotic syndrome (NS) phytohemagglutinin (PHA)-induced lymphocyte proliferation was studied at various stages of the disease. We demonstrated that lymphocyte transformation during acute exacerbation is markedly decreased, especially if cells are cultured in patient serum. During treatment with steroids PHA-stimulation improves. During full remission all patients showed their maximal lymphocyte stimulation. On the basis of these results and reports from the literature we postulate that patients with the NS have a T cell clone which inhibits the transformation capacity of the remaining lymphocytes through production of a heat stable serum factor. The same or a second factor produced by these lymphocytes could at the same time exert a toxic effect on the glomerular basement membrane.

Mechanisms of genetic resistance to Friend virus leukemia in mice. II. Resistance of mitogen-responsive lymphocytes mediated by marrow-dependent cells

Friend leukemia virus suppresses the proliferative responses of normal thymus-dependent (T) and bursa equivalent-dependent (B) lymphocytes from spleen, thymus, lymph node, and bone marrow to mitogens. The suppressive effect of Friend virus complex (FV) requires fully infectious virions. Friend erythroleukemic cells, washed to removed extracellular virus, fail to suppress concanavalin A (Con-A)-induced mitogenesis of normal spleen cells. This indicates that FV does not mediate its immunosuppressive effect via transformed erythropoietic cells. The in vitro suppressive effect of FV on lymphocyte mitogenesis is under host genetic control. Spleen, bone marrow, and thymus cells from strains of mice susceptible to FV-induced leukemogenesis in vivo were quite susceptible to the suppressive effects of FV in vitro. On the other hand, similar cells from strains of mice such as C57BL/6 resistant to Friend erythroleukemia, were quite resistant to in virto immunosuppression by FV. Mitogenesis of splenic T cells from resistant B6 mice, previously treated with 89Sr, became susceptible to suppression by FV. This indicated that the in vitro resistance of lymphocytes to FV-induced suppression is not an intrinsic property of T cells, but is controlled by marrow-dependent (M) cells which are selectively eliminated by treatment with 89Sr. M-cell function does not develop in mice less than 3-wk old. The Con A response by thymus cells from 2-wk-old B6 mice was susceptible to suppression by FV, further supporting the concept that M cells may regulate the genetic resistance to FV.