Murine AIDS is initiated in the lymph nodes draining the site of inoculation, and the infected B cells influence T cells located at distance, in noninfected organs.

The infection of cells which belong to the B-cell lineage is thought to be the primary event leading to the phenotypic and functional alterations seen in the murine AIDS (M. Huang, C. Simard, D. Kay, and P. Jolicoeur, J. Virol. 65:6562-6571, 1991). Using in situ hybridization, we studied the time course of the anatomic distribution of the murine AIDS-infected B cells in C57BL/6 mice inoculated intraperitoneally or in the foot pad with helper-free stocks of the defective murine AIDS virus. The local lymph nodes draining the injection site (the mediastinal or popliteal lymph nodes) were the primary organs in which infected B cells could be detected. From this initial site, the proliferating infected B cells were found to migrate progressively to most of the other lymph nodes and to the spleen. The bone marrow cells (containing the precursor B cells) were not found to be infected by the virus. These results suggest that the defective murine AIDS virus infects mature Ly-1- B cells present in lymph nodes. We compared the concanavalin A response of the T cells at an early time postinoculation, before all lymphoid organs are infiltrated with infected B cells. In lymphoid organs free of infected B cells, T cells were found to be hyperresponsive. In lymphoid organs in which infected B cells were present, T cells were hyporesponsive. These data suggest that infected B cells influence distant T cells, maybe by the release of a circulating factor or through another uninfected cell population activated by the infected B cells.     

Cytolytic T lymphocytes specific for tumors and infected cells from mice with a retrovirus-induced immunodeficiency syndrome.

LP-BM5 retrovirus complex-infected C57BL/6 mice develop immunodeficiency, somewhat analogous to AIDS, termed murine AIDS (MAIDS). After secondary stimulation with syngeneic B-cell lymphomas from LP-BM5-infected mice, C57BL/6 mice produced vigorous CD8+ cytotoxic T lymphocytes specific for MAIDS-associated tumors. An anti-LP-BM5 specificity was suggested because spleen and lymph node cells from LP-BM5-infected mice served as target cells in competition assays, and cells from LP-BM5, but not ecotropic, virus-infected mice functioned as secondary in vitro stimulators to generate cytotoxic T lymphocytes to MAIDS tumors.     

Lactate dehydrogenase-elevating virus replication persists in liver, spleen, lymph node, and testis tissues and results in accumulation of viral RNA in germinal centers, concomitant with polyclonal activation of B cells.

Lactate dehydrogenase-elevating virus (LDV) replicates primarily and most likely solely in a subpopulation of macrophages in extraneuronal tissues. Infection of mice, regardless of age, with LDV leads to the rapid cytocidal replication of the virus in these cells, resulting in the release of large amounts of LDV into the circulation. The infection then progresses into life-long, asymptomatic, low-level viremic persistence, which is maintained by LDV replication in newly generated LDV-permissive cells which escapes all antiviral immune responses. In situ hybridization studies of tissue sections of adult FVB mice revealed that by 1 day postinfection (p.i.), LDV-infected cells were present in practically all tissues but were present in the highest numbers in the lymph nodes, spleen, and skin. In the central nervous system, LDV-infected cells were restricted to the leptomeninges. Most of the infected cells had disappeared at 3 days p.i., consistent with the cytocidal nature of the LDV infection, except for small numbers in lymph node, spleen, liver, and testis tissues. These tissues harbored infected cells until at least 90 days p.i. The results suggest that the generation of LDV-permissive cells during the persistent phase is restricted to these tissues. The continued presence of LDV-infected cells in testis tissue suggests the possibility of LDV release in semen and sexual transmission. Most striking was the accumulation of large amounts of LDV RNA in newly generated germinal centers of lymph nodes and the spleen. The LDV RNA was not associated with infected cells but was probably associated with virions or debris of infected, lysed cells. The appearance of LDV RNA in germinal centers in these mice coincided in time with the polyclonal activation of B cells, which leads to the accumulation of polyclonal immunoglobulin G2a and low-molecular-weight immune complexes in the circulation.     

Adoptive transfer of polyclonal and cloned cytolytic T lymphocytes (CTL) specific for mouse AIDS-associated tumors is effective in preserving CTL responses: a measure of protection against LP-BM5 retrovirus-induced immunodeficiency.

Cytolytic T lymphocytes (CTL) can be raised against C57BL/6 B-cell lymphomas from mice with LP-BM5 murine leukemia virus-induced AIDS (MAIDS). Adoptive transfer of polyclonal anti-MAIDS tumor CTL or two CTL clones specific for the B6-1710 MAIDS lymphoma caused preservation of major histocompatibility complex-restricted and allogeneic CTL responses, which may be interpreted as indices of protection from LP-BM5 murine leukemia virus-induced immunodeficiency.     

Autocrine regulation of IL-12 receptor expression is independent of secondary IFN-gamma secretion and not restricted to T and NK cells.

The biological response to IL-12 is mediated through specific binding to a high affinity receptor complex composed of at least two subunits (designated IL-12Rbeta1 and IL-12Rbeta2) that are expressed on NK cells and activated T cells. The selective loss of IL-12Rbeta2 expression during Th2 T cell differentiation suggests that regulation of this receptor component may govern IL-12 responsiveness. In murine assays, down-regulation of IL-12Rbeta2 expression can be prevented by treatment with IFN-gamma, indicating that receptor expression and hence IL-12 responsiveness may be regulated, at least in part, by the local cytokine milieu. In this study, we report that cellular expression of both IL-12Rbeta1 and beta2 mRNA is increased in the lymph nodes of naive mice following systemic administration of murine rIL-12 (rmIL-12). Changes in IL-12R mRNA were associated with increased IFN-gamma secretion following ex vivo activation of lymph node cells with rmIL-12, indicating the presence of a functional receptor complex. Expression of IL-12R mRNA was not restricted to lymph node T cells, and its autocrine regulation was independent of secondary IFN-gamma secretion. Data from fractionated lymph node cells as well as rmIL-12-treated B cell-deficient mice suggest that IL-12-responsive B cells may represent an alternative cellular source for IFN-gamma production. However, the strength of the biological response to rmIL-12 is not governed solely by receptor expression, as rmIL-12-induced IFN-gamma secretion from cultured lymph node cells is accessory cell dependent and can be partially blocked by inhibition of B7 costimulation.     

CD4+ subset regulation in viral infection. Preferential activation of Th2 cells during progression of retrovirus-induced immunodeficiency in mice.

Progressive lymphoproliferation and increasingly severe immunodeficiency are prominent features of a syndrome, designated mouse AIDS, which develops in susceptible strains of mice infected with the mixture of murine leukemia viruses, termed LP-BM5. Development of splenomegaly and lymphadenopathy, caused primarily by increases in B cell immunoblasts, requires the presence of CD4+ T cells and is assumed to be mediated by lymphokines produced by these cells inasmuch as progression of disease is markedly inhibited by treatment of infected mice with cyclosporin A. Studies of spleen cells from infected mice revealed spontaneous production of cytokines (IFN-gamma, IL-2, IL-4, IL-5, and IL-10) characteristic of Th0 (or a mixture of Th1 and Th2) T helper cells at 1 wk after infection. At later times, IFN-gamma and IL-2, characteristic products of Th1 helper clones, were expressed poorly, either spontaneously or after stimulation of cells with Con A. In contrast, IL-4, IL-5, IL-6, and IL-10, cytokines typically synthesized by Th2 cells, were produced in response to Con A or spontaneously through 18 wk post-infection. Increased serum IgE levels and enhanced IL-10 mRNA expression were consistent with expression of Th2 cytokines at biologically significant levels in vivo. Selective depletion of T cell subsets before stimulation with Con A showed that CD4+ T cells were the primary source of IL-2, IL-4, IL-10, and, to a lesser extent, IFN-gamma in spleens and lymph nodes of normal or infected mice. These results suggest that persistent activation of CD4+ T cells with the lymphokine profile of Th2 helper clones is responsible for chronic B cell stimulation, down-regulation of Th1 cytokines, and impaired CD8+ T cell function in mouse AIDS. This provides the first demonstration that, like many parasitic infections, viruses encoding potent antigenic stimuli can markedly affect the balance of Th subset expression.     

T and B lymphocyte migration into syngeneic tumors.

The migration of splenic T and B lymphocytes into syngeneic tumors undergoing immunologic rejection was investigates. Spleen cells were obtained from normal BALC/c mice or BALB/c mice bearing tumors induced by murine sarcoma virus (MSV). Either whole spleen cells or immunoabsorbent purified T and B cells were radiolabeled with sodium chromate-51 and injected i.v. into normal or MSV inducted-tumor bearing syngeneic recipients. Twenty-four hours later the recipient mice were sacrificed and radioactivity was assessed for tumor, contralateral normal muscle, the lymph nodes draining the tumor and contralateral draining lymph nodes, peripheral lymph nodes, spleen, and liver. Both T and B lymphocytes from either normal or MSV tumor-bearing animals show greatly increased migration into the tumor when compared with normal muscle. Migration of T cells from both normal and MSV tumor bearers was 30 times that of migration to normal muscle. B cells from tumor-bearing mice, on the other hand, localized in the tumor itself only 50% as frequently as did B cells from normal animals. In addition, T cells from MSV tumor bearers were found in the highest proportion in the lymph node draining the tumor site. We conclude that T and B lymphocytes from either normal or tumor-bearing mice migrate to a syngeneic tumor undergoing immunologic rejection. In contrast, the migration of both T and B cells from tumor-bearing animals was decreased to the peripheral lymph nodes at the time of maximum tumor growth.     

CD19 signaling pathways play a major role for murine AIDS induction and progression

Infection of genetically susceptible mice with the LP-BM5 mixture of murine leukemia viruses including an etiologic defective virus (BM5def) causes an immunodeficiency syndrome called murine AIDS (MAIDS). The disease is characterized by interactions between B cells and CD4(+) T cells resulting in polyclonal activation of both cell types. It is known that BM5def is expressed at highest levels in B cells and that B cells serve as viral APC. The CD19-CD21 complex and CD22 on the surface of B cells play critical roles as regulators of B cell responses to a variety of stimuli, influencing cell activation, differentiation, and survival. CD19 integrates positive signals induced by B cell receptor ligation by interacting with the protooncogene Vav, which leads to subsequent tyrosine phosphorylation of this molecule. In contrast, CD22 negatively regulates Vav phosphorylation. To analyze the role of CD19, CD21, Vav, and CD22 in MAIDS, we infected mice deficient in CD19, CD21 (CR2), Vav-1, or CD22 with LP-BM5 murine leukemia viruses. Infected CR2(-/-) mice developed MAIDS with a time course and severity indistinguishable from that of wild-type mice. In contrast, CD19 as well as Vav-1 deficiency restricted viral replication and suppressed the development of typical signs of MAIDS including splenomegaly, lymphadenopathy, and hypergammaglobulinemia. Finally, CD22 deficiency was found to accelerate MAIDS development. These results provide novel insights into the B cell signaling pathways required for normal induction and progression of MAIDS.     

Characterization of the CD154-positive and CD40-positive cellular subsets required for pathogenesis in retrovirus-induced murine immunodeficiency

Genetically susceptible C57BL/6 (B6) mice that are infected with the LP-BM5 isolate of murine retroviruses develop profound splenomegaly, lymphadenopathy, hypergammaglobulinemia, terminal B-cell lymphomas, and an immunodeficiency state bearing many similarities to the pathologies seen in AIDS. Because of these similarities, this syndrome has been called murine AIDS (MAIDS). We have previously shown that CD154 (CD40 ligand)-CD40 molecular interactions are required both for the initiation and progression of MAIDS. Thus, in vivo anti-CD154 monoclonal antibody (MAb) treatment inhibited MAIDS symptoms in LP-BM5-infected wild-type mice when either a short course of anti-CD154 MAb treatment was started on the day of infection or a course was initiated 3 to 4 weeks after LP-BM5 administration, after disease was established. Here, we further characterize this required CD154-CD40 interaction by a series of adoptive transfer experiments designed to elucidate which cellular subsets must express CD154 or CD40 for LP-BM5 to induce MAIDS. Specifically with regard to CD154 expression, MAIDS-insusceptible B6 nude mice reconstituted with highly purified CD4+ T cells from wild-type, but not from CD154 knockout, B6 donors displayed clear MAIDS after LP-BM5 infection. In contrast, nude B6 recipients that received CD8+ T cells from wild-type B6 donors did not develop MAIDS after LP-BM5 infection. B6 CD40 knockout mice, which are also relatively resistant to LP-BM5-induced MAIDS, became susceptible to LP-BM5-induced disease after reconstitution with highly purified wild-type B cells but not after receiving purified wild-type dendritic cells (DC) or a combined CD40+ population composed of DC and macrophages obtained from B6 SCID mouse donors. Based on these and other experiments, we thus conclude that the cellular basis for the requirement for CD154-CD40 interactions for MAIDS induction and progression can be accounted for by CD154 expression on CD4+ T cells and CD40 expression on B cells.     

Human lymphomas transplanted in nude mice

This study was carried out to determine the take rate of malignant lymphomas transplanted subcutaneously in nude mice. Lymphoid tissue from patients with a variety of lymphoproliferative and lymphomatous disorders was employed, but only four (8.3% of total) non-Hodgkin's lymphomas of various types grew in the nude mice. These transplants were from patients with lymphoplasmacytic, lymphoblastic, immunoblastic and centroblastic lymphomas; two of them were serially transferred. High grade malignant lymphomas seem easier to transplant than low grade ones. In each case, the tumor growing in nude mice was similar to the patient's tumor. In one case, metastases were found in mesenteric lymph nodes and lung. Electron microscopic study showed that neoplastic cells were associated with peculiar dark cells the nature of which is discussed. Furthermore, in two transplanted lymphomas, neoplastic cells contained C type virus particles, indicating contamination by the murine xenotropic type C virus.     

Distribution of cycling T lymphocytes in blood and lymphoid organs during immune responses

Proliferation of murine T lymphocytes in blood, lymph nodes, and spleen was studied in four in vivo stimulation systems, using BrdU pulse-labeling of DNA-synthesizing cells. The T cell response to the superantigen Staphylococcus enterotoxin B (SEB) was studied in detail. Vbeta8+ T cells showed a peak of DNA synthesis 16-24 h after SEB injection, and the percentage of BrdU+ CD4 and CD8 T cells was higher in blood than in lymph nodes and spleen. DNA synthesis was preceded by massive migration of Vbeta8+ cells from blood to lymphoid organs, in which the early activation marker CD69 was first up-regulated. SEB-nonspecific Vbeta6+ cells showed minimal stimulation but, when cycling, also expressed a high level of CD69. The other systems studied were injection of the IFN-gamma inducer polyinosinic:polycytidylic acid, infection by the BM5 variants of murine leukemia virus (the causative agent of murine AIDS), and T cell expansion after transfer of normal bone marrow and lymph node cells into recombinase-activating gene-2-deficient mice. In each case, a peak of T cell proliferation was observed in blood. These data demonstrate the extensive redistribution of cycling T cells in the first few hours after activation. Kinetic studies of blood lymphocyte status appear crucial for understanding primary immune responses because cycling and redistributing T lymphocytes are enriched in the circulating compartment.     

The generation of monoclonal anti-idiotype antibodies to human B cell-derived leukemias and lymphomas

We developed murine anti-idiotype monoclonal antibodies for each of four patients with B cell-derived leukemias and lymphomas. Idiotypic immunoglobulin was isolated from mouse X human tumor-cell hybridomas or from patients' serum and was used to immunize mice for the development of murine anti-idiotype monoclonal antibodies. Each patient's anti-idiotype antibodies demonstrated reactivity restricted to the immunizing immunoglobulin, thereby limiting their therapeutic utility to a single individual. In addition, we isolated isotype switch variants of hybridomas producing monoclonal anti-idiotypic antibody. The restricted specificity of these antibodies was found to be of value for the analysis of the extent of malignant B cell infiltration in a variety of tissues from several patients. Large populations of idiotype-bearing cells were detectable in biopsy specimens from patients K.T. and L.H. In contrast, although bone marrow specimens from patient G.D. were apparently devoid of morphologically abnormal cells, a small, highly fluorescent population of cells was demonstrable underscoring the potential utility of these antibodies for posttreatment evaluation as well as for therapy. In a fourth patient, H.M., anti-idiotype antibodies developed against the circulating macroglobulin isolated from his plasma failed to react with either his circulating or bone marrow hairy cell leukemia cells. However, examination of an enlarged inguinal lymph node revealed the presence of a large number of idiotype-bearing cells. Thus, the presence of two distinct malignant B cell clones were discovered in this individual through the use of anti-idiotype monoclonal antibodies. Anti-idiotype antibodies, therefore, represent a highly specific tool for the evaluation and potential therapy of B cell malignancies in individual patients.     

Experimental Trypanosoma cruzi infection alters the shaping of the central and peripheral T-cell repertoire

We investigated the thymic and peripheral T-lymphocyte subsets in BALB/c mice undergoing acute or chronic Trypanosoma cruzi infection, in terms of expression of particular Vbeta rearrangements of the T-cell receptor. We first confirmed the severe depletion of CD4(+)CD8(+) thymocytes following acute T. cruzi infection. By contrast, the numbers of CD4(+)CD8(+) cells in subcutaneous lymph nodes increased up to 16 times. In subcutaneous lymph nodes, we found CD4(+)CD8(+) cells that expressed prohibited segments TCRVbeta5 and TCRVbeta12 (which are physiologically deleted in the thymus of BALB/c mice), as did some mature single-positive cells (CD4(+)CD8(-) and CD4(-)CD8(+)). In the thymus of infected animals, although higher numbers of immature cells bearing such Vbeta segments were seen, they were no longer detected in the mature single-positive stage, suggesting that negative selection occurs normally. We also found increased numbers of cells bearing the potentially autoreactive phenotype TCRVbeta5(+) and TCRVbeta12(+) in T-lymphocyte subsets from subcutaneous lymph nodes of T. cruzi chronically infected mice. In conclusion, our data indicate that immature T lymphocytes bearing prohibited TCRVbeta segments leave the thymus and gain the lymph nodes, where they further differentiate into mature CD4(+) or CD8(+) cells. Conjointly, these findings show changes in the shaping of the central and peripheral T-cell repertoire in both acute and chronic phases of murine T. cruzi infection. The release of potentially autoreactive T cells in the periphery of the immune system may contribute to the autoimmune process found in both murine and human Chagas' disease.     

Common germinal-center B-cell origin of the malignant cells in two composite lymphomas, involving classical Hodgkin's disease and either follicular lymphoma or B-CLL

BACKGROUND: Classical Hodgkin's disease (HD) and B-cell non-Hodgkin lymphoma (NHL) occasionally occur in the same patient. Such composite lymphomas represent interesting models to study the pathogenesis of B-cell lymphomas and the relationship between HD and B-cell NHL. MATERIALS AND METHODS: We analyzed two composite lymphomas (a combination of classical HD with follicular lymphoma [FL] and a combination of classical HD with B-cell chronic lymphocytic leukemia [B-CLL]) by micromanipulation of single cells from tissue sections and amplification of immunoglobulin V region genes for the clonal relationship of the tumor cells. RESULTS: In both cases, clonally related variable (V) genes with both shared as well as distinct somatic mutations were obtained from the two lymphomas, showing that in each of the cases the distinct tumor cells were members of a common germinal center (GC) B-cell clone. FL cells from two different lymph nodes of patient 1 showed a similar mutation pattern, suggesting that infiltration of these lymph nodes by tumor cells was not restricted to a particular FL cell or subclone. In the FL, a single cell was identified with a mutation signature indicating that premalignant cells can persist in the tissue. CONCLUSIONS: The cases presented here further underline the close relationship between HD and B-cell NHL and the role of the GC in lymphomagenesis. Whereas the latter was already suggested for FL and HD, the present study indicates that also in the B-CLL subset characterized by mutated Ig genes, important steps in malignant transformation happen in the GC, and that HRS cells can derive from CD5-positive B cells.     

Immune recognition of AIDS virus antigens by human and murine cytotoxic T lymphocytes

The CTL response to HIV was analyzed in humans and in mice. By using a novel and strictly autologous lymphocyte culture system, human CTL lines were established with PBL from seropositive asymptomatic donors and from patients suffering from AIDS or presenting AIDS-related complex. CTL from HLA-A2 donors recognize and kill murine P815 mastocytoma cells doubly transfected with the human HLA-A2 gene and the HIV env gene; they also kill HLA-compatible human macrophages infected with HIV. CTL specific for the HIV env Ag were also generated in BALB/c mice by immunization with syngeneic murine cells transfected with the HIV env gene. Human and murine HIV-immune CTL populations belong to the CD8 subset of T lymphocytes and are restricted by class I HLA or H-2 transplantation Ag, respectively, in the recognition of HIV env Ag. The two different experimental systems presented here can be used to study CD8 lymphocyte immunity against HIV. The murine model of CTL immunity offers the additional advantage of avoiding the manipulation of infectious virus isolates.     

T cell regulation of polyclonal B cell responsiveness. I. Helper effects of T cells.

Polyclonal activation of murine splenic B lymphocytes to secrete immunoglobulin was shown to be subject to regulation by splenic T cells. By admixture of separated B and T cell populations it was demonstrated that normal fresh splenic T cells were able to augment polyclonal B cell responsiveness to LPS up to several-fold. Optimal collaboration between these two cell types ensued when they were co-cultured in equal numbers. T cell-mediated enhancement of polyclonal B cell responses was dependent upon the ability of T cells to divide and was manifested upon T cell interaction with B cells soon after culture initiation. Originally expounded as a one-signal phenomenon, polyclonal activation of lymphocytes by LPS is, under the circumstances described, attributable instead to two distinct, nonspecific signals acting in concert. The observation that T cells from LPS-nonresponder (C3H/HeJ) mice were deficient in the capacity to enhance polyclonal B cell responsiveness of B cells derived from responder (C3H/HeN) mice implied a direct action of LPS on the involved T cells as well as an active role for the T cell signal in this immunoregulatory event. The novel observation of a functional T cell defect in LPS responsiveness in the C3H/HeJ mouse is discussed in terms of its other cellular defects.     

Impaired calcium mobilization in CD4+ and CD8+ T cells in a retrovirus-induced immunodeficiency syndrome, murine AIDS.

After infection with LP-BM5 murine leukemia viruses, susceptible strains of mice develop a severe and progressive immunodeficiency disease, termed murine AIDS (MAIDS), features of which include markedly impaired T cell response to mitogens or specific Ag stimulation and decreased production of IL-2. Since an elevation of intracellular calcium concentration resulting from binding of Ag to the TCR is associated with IL-2 production, T cells from mice either uninfected or infected with LP-BM5 murine leukemia viruses were examined by a calcium mobilization assay. Both CD4+ and CD8+ T cells from infected mice manifested impaired calcium mobilization responses upon in vitro stimulation with anti-CD3 mAb or Con A. The abnormalities appeared early after virus inoculation and showed no difference in time course between subsets of T cells. Frequencies of prestimulation calcium-positive cells among both CD4+ and CD8+ cells in mice with MAIDS were significantly higher than those for uninfected mice. These abnormalities were associated with presence of the MAIDS-inducing defective virus genome, but were not induced by infection of mice genetically resistant to development of MAIDS or with nonpathogenic helper murine leukemia virus, a virus component that induces high spontaneous proliferation of T cells, even in MAIDS-resistant mice.     

Indiscriminate representation of VH-gene families in the murine B lymphocyte responses to Trypanosoma cruzi

The utilization of the nine major homology families of VH-genes was quantitated in the B lymphocyte response to Trypanosoma cruzi infection of C57BL/6 mice. Normal and infected mice at various times after parasite inoculation were compared for VH-gene distribution of CFU-B produced by activated blasts recovered from spleen and lymph nodes, and for relative hybridization of total spleen RNA with each of the family probes. T. cruzi infection results in large increases of splenic RNA in the various homology families, and the numbers of activated CFU-B, reflecting the massive B lymphocyte responses. In acute phase, all nine families are expressed in roughly the same proportions as in normal mice, whereas in chronic infection, B cells expressing S107 and 7183 VH-genes might be preferentially stimulated. These results establish the polyclonal nature of the host response to T. cruzi infection.     

Atrophy of mesenteric lymph nodes in experimental Chagas' disease: differential role of Fas/Fas-L and TNFRI/TNF pathways

It is currently accepted that experimental acute infection by Trypanosoma cruzi promotes changes in secondary lymphoid organs, with general T and B lymphocyte polyclonal activation. Here we show that mesenteric lymph nodes (MLN) of acutely infected mice show severe atrophy due to extensive lymphocyte apoptosis. Accordingly, clusters of apoptotic cells are detected in the initial phase of infection in MLN but not in subcutaneous nodes. Moreover, such atrophy is independent of the infection route, parasite load or the mouse strain used. Studies in Fas-L deficient (BALB gld/gld+/+) and in TNF type 1 receptor (p55-/-) knockout mice indicate that both molecules are involved in MLN atrophy: Fas-L participates in cell death of CD4+ as well as B lymphocytes, whereas the TNF type 1 receptor is important for the apoptosis of CD4+ and CD8+ T lymphocytes. In contrast, perforin does not play a role, as lymph nodes from perforin-deficient mice do not behave differently from the corresponding wild types. Our data support the concept that, even in a systemic infection, differential (even opposing) responses can be found in different lymph node chains.