STUDIES ON IMMUNOLOGICAL TOLERANCE TO LCM VIRUS. 4. THE QUESTION OF IMMUNITY IN ADOPTIVELY IMMUNIZED VIRUS CARRIERS

Hypogammaglobulinemia and exacerbated CD8 T-cell–mediated immunopathology in SAP-deficient mice with chronic LCMV infection mimics human XLP disease

The human genetic disease X-linked lymphoproliferative disease (XLP), which is caused by mutations in SH2D1A/SAP that encode SLAM-associated protein (SAP), is characterized by an inability to control Epstein-Barr virus (EBV) and hypogammaglobulinemia. It is unclear which aspects of XLP disease are specific to herpesvirus infection and which reflect general immunologic functions performed by SAP. We examined SAP– mice during a chronic LCMV infection, specifically to address the following question: Which SAP deficiency immunologic problems are general, and which are EBV specific? Illness, weight loss, and prolonged viral replication were much more severe in SAP– mice. Aggressive immunopathology was observed. This inability to control chronic LCMV was associated with both CD8 T-cell and B-cell response defects. Importantly, we demonstrate that SAP– CD8 T cells are the primary cause of the immunopathology and clinical illness, because depletion of CD8 T cells blocked disease. This is the first direct demonstration of SAP– CD8 T-cell–mediated immunopathology, confirming 30 years of XLP clinical observations and indirect experimentation. In addition, germinal center formation was extremely defective in chronically infected SAP– animals, and hypogammaglobulinemia was observed. These findings in a chronic viral infection mouse model recapitulate key features of human XLP and clarify SAP's critical role regulating both cellular and humoral immunity.

Exhaustion of cytotoxic T cells during adoptive immunotherapy of virus carrier mice can be prevented by B cells or CD4+ T cells

Rapid disappearance of antiviral CTL after transfusion into persistently infected individuals is a serious limitation of adoptive immunotherapy protocols. In the mouse model of persistent infection with lymphocytic choriomeningitis virus (LCMV) naive or immune virus-specific donor CD8+ T cells are exhausted after transfusion into carrier recipients with similar kinetics. Here we show that cotransfusion of immune CD4+ T cells prevents exhaustion of immune CD8+ T cells. Interestingly, cotransfer of primed B cells also prevented CD8+ T cell exhaustion in carriers even in the absence of T helper cells. This effect required the presence of immune B cells as repetitive treatment with hyperimmune serum led to the generation of antibody escape mutants. A combination of primed CD4+ T cells and primed B cells enhanced antiviral effects and prevented exhaustion also of naive CD8+ T cells. One key factor for prevention of CD8+ T cell exhaustion was the antiviral effect of the cotransfused cells thus reducing the time that CD8+ T cells are confronted with a high systemic viral load. These findings have implications for improving adoptive immunotherapy for persistent human viral infections.

A critical role for neutralizing-antibody-producing B cells, CD4(+) T cells, and interferons in persistent and acute infections of mice with lymphocytic choriomeningitis virus: implications for adoptive immunotherapy of virus carriers

This study demonstrates that neutralizing-antibody-producing B cells, CD4(+) T cells, and interferons (IFNs) are of key importance in virus control both in adoptive immunotherapy of persistent infection and in the late phase of acute infection with the WE strain of lymphocytic choriomeningitis virus (LCMV). We report the following results. (i) Clearance of LCMV-WE from C57BL/6 carrier mice by adoptive transfer of memory spleen cells requires B cells and CD4(+) T cells but not necessarily CD8(+) T cells. (ii) At the doses examined, CD8(+) T cells contribute to the initial reduction of viral titers but are alone not sufficient to clear the virus because they are exhausted. (iii) In the presence of functional IFN-gamma, virus clearance correlates well with the generation of neutralizing antibodies in the treated carrier mice. (iv) In the absence of receptors for IFN-gamma, virus clearance is not achieved. (v) Adoptive immunotherapy of mice persistently infected with a distinct virus isolate, LCMV-Armstrong, revealed only low levels of neutralizing antibodies; in this case, CD8(+) T cells were needed for virus clearance in addition to B and CD4(+) T cells. (vi) After low dose infection of C57BL/6 mice with LCMV-WE, virus is eliminated below detectable levels by CD8(+) T cells, but long-term (>2 months) virus control is usually not achieved in the absence of B cells or CD4(+) T cells; reappearance of the virus is paralleled either by exhaustion of virus-specific cytotoxic T lymphocytes or lethal immunopathology. These findings are of importance for adoptive immunotherapy strategies against persistent virus infections in humans.

Effective clearance of a persistent viral infection requires cooperation between virus-specific Lyt2+ T cells and nonspecific bone marrow-derived cells

The lifelong chronic lymphocytic choriomeningitis virus (LCMV) infection established in neonatally or congenitally infected mice can be eliminated by adoptive transfer of lymphoid cells from LCMV-immune mice. In this study, we have identified the effector cells mediating the clearance of persistent and disseminated LCMV infection. Using mice that are recombinant in the H-2 region and by selective depletion of lymphocyte subpopulations, we show that viral clearance was mediated by LCMV-specific Lyt2+ L3T4- T cells that are restricted to the class I genes of the major histocompatibility complex. In addition, our results show a requirement for host-derived bone marrow cells for the effective elimination of virus from the liver. These studies emphasize the importance of virus-specific T cells and an intact bone marrow function in viral clearance.

High-dose survival in the lymphocytic choriomeningitis virus infection is accompanied by suppressed DTH but unaffected T-cell cytotoxicity

Provided that intracerebral inoculation is applied, an increase in the virus dose from 10(2) to 10(4) LD50 of lymphocytic choriomeningitis virus (LCMV) leads to strikingly reduced mortality. To analyse the background for this autointerference, we measured several virologic and immunologic variables in mice infected with these doses of virus. In the high-dose mice we found generally higher organ virus titres and serum interferon titres than in the low-dose mice. Since we could demonstrate that virus-specific T-cell cytotoxicity in spleen, peripheral blood, and meningeal exudate was similar after intracerebral infection with large and small virus doses, and since the LCMV infection in the brain qualitatively and quantitatively was independent of the size of virus inoculum, the explanation for the survival of the high-dose animals is obviously not lack of possibilities for interaction between cytotoxic T cells and infected sensitive targets in the central nervous system. On the other hand, high doses of virus caused a clear suppression of the LCMV-specific delayed-type hypersensitivity (DTH). In addition, when splenocytes from high-dose animals were transferred either intravenously or locally into the footpad of newly virus-challenged mice, DTH was markedly suppressed as compared with the response after transfer of spleen cells from low-dose mice. We therefore conclude that autointerference in the LCMV infection is due to a selective suppression of Td function. Large amounts of persistent virus late after infection with high doses of virus suggest a central role for Td function also in virus clearance. Finally, our results indicate the existence of two subsets of K,D region-restricted T cells, one mediating cytotoxicity and the other mediating DTH. This possibility is discussed.

Lymphocytic choriomeningitis virus killer T cells are lethal only in weakly disseminated murine infections

Two types of lymphocytic choriomeningitis (LCM) viruses were studied which, upon intracerebral injection into adult C3H mice, provoked either (a) acute fatal central nervous system (CNS) disease or (b) life-long persistent infection. Both virus types, (a) aggressive and (b) docile, had been found to induce LCM-specific lymphocytes with comparable in vitro lytic activity (11). Because the requirement for T cells in the development of adult LCM disease has been extensively documented, we sought other reasons for the lack of acute disease in mice infected with docile virus. A striking correlation was found between the outcome of the infection and spread of virus to visceral organs. Adoptive transfer experiments showed that a 300-plaque forming unit inoculum of docile virus induced a population of T cells in donor mice fully capable of causing CNS disease in identically infected recipients. This disease causing ability was lost if the interaction was delayed beyond 3 d after infection of the recipients, but could be preserved by lowering the size of the viral inoculum in the recipients. Furthermore, without adoptive transfer, very low intracerebral doses of docile virus (which mimicked the normally slow spread of aggressive virus) were lethal. On the other hand, very high doses of aggressive virus, which mimicked the normally rapid spread of docile virus, did not induce fatal CNS disease. The results suggest that rapid dissemination of the LCM infection creates multiple target organs which divert the focused lethal T cell attack on the brain.

Cytotoxic T cells are induced in mice infected with lymphocytic choriomeningitis virus strains of markedly different pathogenicities

The ability of two lymphocytic choriomeningitis virus substrains to induce cytotoxic T-lymphocyte (CTL) responses in intracerebrally infected mice was examined. One strain, designated A (aggressive), provoked a convulsive type of death in 100% of the mice within 8 to 9 days, whereas the other strain, designated D (docile), killed less than 10% of the mice during 28-day observation periods. CTL activity was assessed by the capacity of partially purified splenocytes to lyse 51Cr-labeled L-cell targets infected with either type of lymphocytic choriomeningitis substrain. The CTL population was identified by its sensitivity to anti-Thy-1 serum and its inability to lyse uninfected target cells or infected target cells with which it differed at the level of antigens controlled by the major histocompatibility gene complex. A strong CTL response developed in mice infected with either lymphocytic choriomeningitis substrain, although the activity provoked by substrain D was somewhat less than that seen after substrain A infection. Peak CTL activities induced by both strains occurred at about the same time. Even though docile virus replicated more extensively in the brain than did aggressive virus and fluorescent antibody staining revealed similar distributions of viral antigen, no inflammatory response was noted in the brains of mice infected with docile virus. These results are discussed with regard to the role of CTLs in mediating classic central nervous system pathology.

Concanavalin A-mediated in vitro activation of a secondary cytotoxic T-cell response in virus-primed splenocytes

In a recent report it was shown that what appeared to be secondary cytotoxic T cells could be obtained from lymphocytic choriomeningitis virus (LCMV)-primed splenocytes after stimulation in vitro with the non-specific T cell mitogen concanavalin A (Con A). The present experiments attempt to characterize further these effector cells and, in particular, to establish whether the Con A-activated cytotoxic effectors are qualitatively different from the secondary cytotoxic T cells induced by restimulation with the homologous antigen. It was found that: (1) in vitro activation with Con A could be obtained with populations harvested between 13 days (the earliest tested) and at least 300 days after priming; (2) cytotoxicity was independent of the presence of carried-over Con A in the cytotoxicity assay; (3) cytotoxicity was dependent on close association between activated T cells and target cells, since no evidence was found to indicate a role for other cell types or soluble (cytotoxic or arming) factors; (4) cytotoxicity was specific with regard to both virus and 'self'. By comparison with previous data on LCMV-induced cytotoxic T cells, it is concluded that Con A induces the generation of cytotoxic T cells from LCMV-primed splenocytes, which, by the criteria used, are indistinguishable from virus-induced secondary cytotoxic T cells. The implications of these findings are discussed.

Immunological unresponsiveness of nude mice to LCM virus infection

The acute LCM infection in nude mice runs a course which is clinically inapparent, and neither a humoral nor a cell-mediated immune response could be detected. Furthermore, during this infection the blood virus titers reached extremely high values. These observations are contrary to what is seen when ordinary normal mice are infected with the LCM virus but identical with the events following infection of ordinary but immune-deficient mice. Despite the absence of immune responses to the virus in the nude mice the very high virus titers obtained within the first few days of the infection declined somewhat during the following weeks. This and the other observations made are discussed briefly in the light of the current hypothesis concerning the immune status of the nude mice and the pathogenesis of the LCM virus infection in mice.

Evaluation of bis-benzimidazoles in the treatment of murine lymphocytic choriomeningitis virus infections

Seventy percent of the mice receiving (S,S)-1,2-bis(5-methoxy-2-benzimidazolyl)-1,2-ethandiol (A36683) in their drinking water lived at least four times longer than control mice when infected with 10 or 100 mean lethal doses of lymphocytic choriomeningitis virus strain UBC. In the next 4 months, most of the survivors died with lymphocytic choriomeningitis-like symptoms. Drug treatment during the first 7 days after infection was found to have no significant effect on virus titers in various organs. The sparing effect of the drug is discussed in terms of immunosuppression.

Studies on cell-mediated immunity to lymphocytic choriomeningitis virus in mice

A large amount of experimental evidence has already been presented indicating the great importance of the cell-mediated immunity in the pathogenesis of the LCM virus infection in mice. In this laboratory a method which makes it possible to measure this cellular immunity quantitatively in vitro has been developed. The method is based on the determination of the radioisotope released after the interaction between specifically sensitized lymphocytes and syngeneic (1)Cr-labeled LCM virus-infected target cells. By using this technique the time-course of the cell-mediated immunity has been established in acutely infected mice and in virus carriers adoptively immunized with syngeneic sensitized lymphocytes. Lymphocytes from acutely infected mice showed a strong lysing effect on the target cells, with a sharp maximum at about the 9th day after infection. The cell-mediated immunity in adoptively immunized virus carrier mice showed the same time-course, but in these animals the lytic effect of the lymphoid cells was considerably less pronounced. Lymphocytes from untreated virus carriers did not, however, have any effect on the target cells, and in these animals it was not possible to demonstrate any evidence of enhancing antibodies, In experiments employing serial dilutions of sensitized lymphocytes in normal cells a direct linear relationship between the number of sensitized lymphocytes and target cell destruction was found. These experiments seem to indicate that the underlying mechanism in the cytotoxic reaction is a direct cell-to-cell interaction.

Phospholipid synthesis in HeLa cells exposed to immunoglobulin G and complement

1. HeLa cells were cultured in the presence of heterologous immunoglobulin G and guinea-pig serum together with [(32)P]phosphate. 2. Incorporation of [(32)P]phosphate was significantly stimulated by anti-HeLa immunoglobulin G and complement-sufficient serum compared with immunoglobulin G from unimmunized rabbits and complement. Within 2.5h heat-inactivated guinea-pig serum and anti-HeLa immunoglobulin G stimulated [(32)P]phosphate incorporation to the same extent as heat-inactivated complement and immunoglobulin G from unimmunized rabbits. 3. Compared with cells exposed to immunoglobulin G from unimmunized rabbits together with complement, anti-HeLa immunoglobulin G with complement increased the phospholipid content of HeLa cells twofold within 5h of incubation. 4. Exposure of HeLa cells to anti-HeLa immunoglobulin G and complement for 5-22h resulted in a twofold increase in the net accumulation of [(32)P]phosphate in sphingomyelin and phosphatidylcholine and a 50% increase in the net accumulation of [(32)P]phosphate in phosphatidylethanolamine, compared with cultures exposed to immunoglobulin G from unimmunized rabbits and complement. 5. A transient accumulation of (32)P-labelled lysophosphoglycerides in HeLa cells exposed to antibody and complement was detected, confirming previous findings (Güttler & Clausen, 1969b). 6. The stimulation of [(32)P]phosphate turnover occurred in cells filling up their cytoplasma with vacuoles. This supports the suggestion that the accumulation of phospholipid in these cells may be concerned with the synthesis and function of cytomembranes.

Immunopathogenesis of acute central nervous system disease produced by lymphocytic choriomeningitis virus. II. Adoptive immunization of virus carriers

Lymphocytic choriomeningitis (LCM) virus carriers were established by intracerebral inoculation of adult BALB/c mice followed by a single dose of cyclophosphamide (CY) (150 mg/kg) 3 days after infection, and by intracerebral injection within 24 hr of birth. These carriers were then adoptively immunized with spleen cells or serum from immune or normal BALB/c donors. Transfer of immune spleen cells into drug-induced carriers consistently resulted in acutely fatal choriomeningitis, histologically strikingly similar to classical LCM. Normal spleen cells or immune serum failed to produce either central nervous system (CNS) pathology or illness with any regularity. In addition, focal necrosis of the cerebellum was seen after adoptive immunization of drug-induced carriers but only when mice received cells at least 3 wk after inoculation, which is probably explained by the gradual spread of infection from membranes to the neural parenchyma during the first month after establishment of the carrier state in adult mice. Immune spleen cells, when transferred to neonatal carriers, led to a decrease in virus titers in blood and brains and to development of antibody without acute CNS disease. It appears that the production of fatal choriomeningitis after LCM infection is determined in part by the distribution of viral antigen, and this is markedly different in neonatal and drug-induced carriers at the time of cell transfer. Another factor of potential importance is the much higher level of circulating viral antigen in the plasma of neonatal than in that of drug-induced LCM carriers. Classical LCM disease can only be transferred by immune lymphoid cells and not by antiserum. Furthermore, little or no complement-fixing (CF) antibody was found in the plasma of mice dying of acute choroiditis. These observations strongly suggest that acute choroiditis is dependent upon the cell-mediated immune response.

Immunopathology of lymphocytic choriomeningitis viurs infection of newborn mice. Antithymocyte serum effects on glomerulonephritis and wasting disease

Antithymocyte serum, when administered neonatally to mice, delayed the maturation of the lymphoid system, permitting development of cellular tolerance to LCM virus at an older age than is ordinarily possible. Humoral antibody formation was not prevented and the animals exhibited the paradox of high titers of both circulating virus and antibody. This, in turn, was followed by a chronic immunopathologic glomerulonephritis in most animals. Some animals developed wasting disease between 1 and 2 months of age, characterized by reticular cell hyperplasia and widespread infiltration into tissues and organs.

The provocation of latent lymphocytic choriomeningitis virus infections in mice by treatment with antilymphocytic serum

The hypothesis that treatment with antilymphocytic serum (ALS) can provoke latent virus infections has been investigated. In adult mice infections with sublethal doses of LCM virus usually result in the development of immunity to the virus and at the same time to a prolonged latent infection. In the experiments described an intensive treatment with large doses of ALS was given to mice which had recovered from LCM virus infection. At the beginning of the treatment the mice had high titers of complement-fixing antibodies in their blood and no detectable virus. The data presented show that in spite of the immunity the ALS treatment provoked the occult virus and led to the development of viremia in all the treated mice. In some, very high virus titers were demonstrable. When the ALS treatment was discontinued the viremia disappeard again. In most of the mice the ALS did not suppress the complement-fixing antibody titers and in some there was even a considerable increase in titer. In such cases the increases in virus titers and in antibody titers were closely related to one another. These results demonstrate once again that the complement-fixing antibodies to the LCM virus in mice probably do not influence the virus.