Nephritogenicity of the lprcg gene on the MRL background.

The novel lymphoproliferative and autoimmune lprcg gene, originally discovered in the CBA/K1Jms (CBA) strain of mice, was transferred onto the MRL/MpJ (MRL) strain background, and the resultant partially congenic MRL-lprcg/lprcg carrying 93% or more MRL genomes on average were examined for immune-complex glomerulonephritis and serological aberrations. Ordinary histological studies revealed that MRL-lprcg/lprcg mice developed glomerulonephritis histologically indistinguishable from that in MRL-lpr/lpr but at a lower frequency than in MRL-lpr/lpr mice. Glomerular immune complex deposition was almost the same in MRL-lprcg/lprcg and MRL-lpr/lpr mice. The levels of serum Ig, circulating immune complexes and autoantibodies in MRL-lprcg/lprcg were comparable to or even higher than those in MRL-lpr/lpr mice. Comparison of the serological abnormalities between MRL-lprcg/lprcg with glomerulonephritis and CBA-lprcg/lprcg without it evidenced the enhanced class switch from IgM to IgG responses in both class-specific autoantibody responses and serum Ig levels in MRL-lprcg/lprcg as in MRL-lpr/lpr mice. These results taken together indicate that the lprcg gene functions in much the same manner as lpr in induction of glomerulonephritis and serological abnormalities on the MRL background as expected from the allelism between the two mutant genes.     

A pivotal role of cell-bound but not soluble CD4 molecules in full development of lupus-like manifestations in MRL-Fas(lprcg)/Fas(lprcg) mice

The role of CD4 molecules in the autoimmune and lymphoproliferative syndrome caused by murine Fas mutations was studied using the novel systemic lupus erythematosus (SLE) model, MRL-Fas(lpr(cg))/Fas(lprcg) (MRL-lpr(cg)) mice, in combination with the novel mutant CD4 gene producing soluble CD4 (sCD4) instead of membrane-bound CD4 (mCD4). For this purpose, various autoimmune manifestations were compared among MRL-lpr(cg) mice homozygous (CD4slprcg), heterozygous (CD4s/mlpr(cg)), and wild-type (CD4mlpr(cg)) for the CD4 mutation. The mortality, glomerulonephritis, proteinuria, and lymphadenopathy were significantly ameliorated in CD4slprcg compared with CD4mlpr(cg) and CD4s/mlpr(cg) mice, both being comparable in these clinical characteristics. In parallel with the clinical improvement, the serum levels of immunoglobulin, anti-DNA antibodies, anti-nuclear antibodies and immune complexes, and the extent of glomerular immune deposition, were significantly lower in the former. The results indicate that mCD4 is important and can not be replaced by sCD4 in full development of SLE-like manifestations, and suggest that CD4+ T cells may aggravate the autoimmune disease by stimulating autoreactive B cells to produce autoantibodies through their helper activity in Fas mutant models. The sCD4 levels in the serum and spleen elevated with the increased accumulation of B220+CD4-CD8- (double-negative (DN)) T cells in CD4slpr(cg) mice. This, together with the significantly milder lymphadenopathy associated with lower DN T cell contents in CD4slpr(cg) than CD4mlpr(cg) mice, implies that some of abnormal DN T cells may be derived from cells of the CD4 lineage.     

Characterization of Mouse Mammary Tumour Virus-Induced Migration of Lymphoid Cells into Lymph Nodes

We previously found that Mtv-2+ lymph nodes (LN) implanted into Mtv-2- mice underwent marked hyperplasia owing to the influx of lymphocytes. LN grafts infected with exogenous mouse mammary tumour viruses (MMTV), MMTV(FM) transmitted by FM mice and MMTV-2 produced by Mtv-2, also swelled in MMTV-free recipients. Mtv-3 and Mtv-7 also displayed this capability. Mtv-2-induced LN hyperplasia was earlier in onset and greater in extent when major histocompatibility complex (MHC) class II I-E was expressed than unexpressed. Mtv-3-induced LN hyperplasia was suppressed completely by Mtv-3 from a different mouse strain and partially by Mtv-6 slightly different from Mtv-3 in superantigen (SAg) Vbeta specificity. LN hyperplasia occurred bidirectionally in LN transplantation between mice carrying Mtv-2 and Mtv-3, which are different SAg Vbeta specificity. LN hyperplasia induced by MMTV-2 carrying SAg responsive to Vbeta14 alone and MMTV(FM) carrying SAg responsive to Vbeta14 and Vbeta8.2 was completely but partially suppressed by MMTV(FM) and MMTV-2, respectively. CD4+ T cells were essential for MMTV-induced LN hyperplasia. LN in situ also underwent significant hyperplasia when infected with MMTV. Thus, MMTV SAg may entice circulating lymphocytes into lymphoid organs and contribute to more efficient dissemination MMTV in vivo. Secondary lymphoid tissue chemokine (SLC) may not be directly involved in this event.     

Characterization of two infectious mouse mammary tumour viruses: superantigenicity and tumorigenicity

Mouse mammary tumour virus (MMTV) is a type B retrovirus that causes mammary tumours in susceptible mice. MMTV encodes a superantigen (SAg) that has the property of stimulating T-cell populations expressing a particular variable region of the T-cell receptor (TCR) beta chain (Vbeta) and needs to be presented in the context of major histocompatibility complex (MHC) class II molecules. Previously, we described two exogenous MMTV, MMTV BALB14, which encodes a superantigen that induces the deletion of Vbeta14+ Tcells, and MMTV BALB2, which encodes a SAg that induces the deletion of Vbeta2+ Tcells. We now describe their biological activity: the deletions involve both CD4+ and CD8+ populations, are progressive and can be detected in blood, lymph nodes and spleen. Such deletions reflect, at least in part, those occurring during intrathymic development. Both BALB2 and BALB14 viral variants are capable of inducing a strong increase of Vbeta-specific T cells in BALB/c mice (I-A+, I-E+). However, when injected into the footpad, their initial stimulatory capacity differs in that the presence of MHC I-E molecules is essential only for the stimulation of Vbeta2+ T cells. Both viral variants are able to induce deletion even in the absence of the I-E molecule in which case, however, deletion appears later and is less pronounced. Both exogenous MMTVs induce, at the end of a year, 30-35% of pregnancy-dependent mammary adenocarcinomas.     

Pairing of Vbeta6 with certain Valpha2 family members prevents T cell deletion by Mtv-7 superantigen

Superantigens (SAg) are proteins of bacterial or viral origin able to activate T cells by forming a trimolecular complex with both MHC class II molecules and the T cell receptor (TCR), leading to clonal deletion of reactive T cells in the thymus. SAg interact with the TCR through the beta chain variable region (Vbeta), but the TCR alpha chain has been shown to have an influence on the T cell reactivity. We have investigated here the role of the TCR alpha chain in the modulation of T cell reactivity to Mtv-7 SAg by comparing the peripheral usage of Valpha2 in Vbeta6(+) (SAg-reactive) and Vbeta8.2(+) (SAg non-reactive) T cells, in either BALB/D2 (Mtv-7(+)) or BALB/c (Mtv-7(-)) mice. The results show, first, that pairing of Vbeta6 with certain Valpha2 family members prevents T cell deletion by Mtv-7 SAg. Second, there is a strikingly different distribution of the Valpha2 family members in CD4 and CD8 populations of Vbeta6 but not of Vbeta8.2 T cells, irrespective of the presence of Mtv-7 SAg. Third, the alpha chain may play a role in the overall stability of the TCR/SAg/MHC complex. Taken together, these results suggest that the Valpha domain contributes to the selective process by its role in the TCR reactivity to SAg/MHC class II complexes, most likely by influencing the orientation of the Vbeta domain in the TCR alphabeta heterodimer.     

Significant role of Fas ligand-binding but defective Fas receptor (CD95) in lymph node hyperplasia composed of abnormal double-negative T cells

The functional differences between two mutations of the Fas (CD95) locus, Faslpr (lpr) and Faslprcg (lprcg), were investigated using bone marrow (BM) transplantation on the C3H mouse background. Both lpr/lpr and lprcg/lprcg BM transferred caused lymph node (LN) hyperplasia in lpr/+ and lprcg/+ recipients, although it was clearly smaller than that in lpr/lpr and lprcg/lprcg recipients of lpr/lpr and lprcg/lprcg BM. In addition, both BM induced significantly larger LN hyperplasia in lprcg/+ than lpr/+ recipients. Appearance of CD4- CD8-[double negative (DN)] T cells in the periphery is the most consistent phenotype of Fas mutations. Importantly, the proportion of DN T cells was higher in larger LN hyperplasia in the order of lpr/+, lprcg/+ and lpr/lpr or lprcg/lprcg recipients. On the other hand, both lpr/lpr and lprcg/lprcg BM transferred into wild-type (+/+) mice caused marked LN atrophy. The former, but not the latter, induced wasting syndrome. Faslg1d (gld)-homozygous lpr/lpr BM transferred into +/+ mice elicited LN hyperplasia of the same extent as that in lpr/lpr mice transferred with lpr/lpr BM, but not wasting syndrome. Taken together with the fact that DN T cells massively express Fas ligand (FasL), this study implied that FasL overexpressed on DN cells may be involved in the accumulation of DN T cells in LN, LN atrophy and wasting syndrome, and that lprcg Fas, which can bind to Fas ligand but not transduce apoptosis signal into cells, may modulate these pathological conditions by interfering with the binding of FasL to Fas.     

Differences between two strains of myelin basic protein (MBP) TCR transgenic mice: implications for tolerance induction

Experimental autoimmune encephalomyelitis (EAE) is mediated by CD4+ T cells which preferentially use the Vbeta8.2 TCR in response to myelin basic protein (MBP). Two strains of Tg mice (Valpha2.3/Vbeta8.2 and Valpha4/Vbeta8.2) have T cell receptors that recognize the NAc1-11 immunodominant epitope of MBP. We previously reported that oral administration of MBP protects both Valpha2.3/Vbeta8.2 and Valpha4/Vbeta8.2 mice from EAE; however, tolerance induction differs between strains and is dependent on the timing of oral antigen. Here we analyze the peripheral and gut-associated lymphoid tissue (GALT) environments of the two strains of Tg mice. Tg cells in the Peyer's patch (PP) but not the spleen of Valpha2.3/Vbeta8.2 mice demonstrate increased CD69 and decreased CD45RB relative to Valpha4/Vbeta8.2 mice. High levels of Th1 and Th2 cytokines, proliferative activity and CC chemokines (MCP-1) are observed in the periphery and GALT of Valpha2.3/Vbeta8.2 Tg mice. In contrast, more non-Tg CD4+ cells are seen in the PP of Valpha4/Vbeta8.2 mice. These studies suggest that activated Tg T cells and fewer potential regulatory cells in the PP of Valpha2.3/Vbeta8.2 Tg mice may influence oral tolerance.     

A crucial role of the thymus in induction by the lprcg gene of lymphadenopathy with autoimmunity in the mouse.

The new mutation at the lpr locus, lprcg, induces massive lymphoproliferation characterized by the selective expansion of CD4-, CD8-, B220+, Thy-1+ cells or double-negative T lymphocytes and production of autoantibodies as does lpr. The thymus is necessary for the induction of anomalous double-negative T lymphocytes and autoimmune symptoms by lpr. To determine whether or not the thymus is also indispensable to expression of the function of lrpcg, lprcg homozygous athymic nude mice (lprcg/lprcg nu/nu; lprcg nudes) were constructed by crossing CBA/KlJms-lprcg/lprcg (CBA-lprcg) and DDD/l-nu/nu mice and observed for lymphoid organ hyperplasia and autoantibody production with or without thymus grafts from various strains of mice including CBA-lprcg. Neither lymphoproliferation nor significantly increased production of autoantibodies was observed in unmanipulated lprcg nudes. In contrast, thymus grafts of both +/+ and lprcg/lprcg genotypes caused lymphoid organ hyperplasia composed of anomalous double-negative T lymphocytes and significantly augmented the production of antibodies against single-stranded DNA (ssDNA). Interestingly, serum Ig and anti-ssDNA antibody levels rose in response to thymus grafts only in IgG but not in IgM classes. These results indicate that the thymus plays a crucial role in the induction of abnormal T-cell differentiation by lprcg and that thymic genotype is irrelevant.     

An allogeneic microenvironment influences the phenotype of intermediate T-cell receptor cells expanding in MRL-lpr/lpr mice.

MRL-lpr/lpr (lpr) mice fall victim to autoimmune disease owing to a lymphoproliferative disorder mainly of double-negative (DN) CD4- CD8- alpha beta T cells expressing a low density of interleukin-2 receptor beta-chain (IL-2R beta). It was previously revealed that the lpr gene is a defective Fas gene, into which an early transposon (ETn) of retrovirus is transfected. As a result of the failure of apoptosis, intermediate T-cell receptor (TCR) cells (i.e. TCRint cells) with DN phenotype abnormally accumulate in the periphery of lpr mice. We investigated herein how these TCRint cells are selected in terms of CD4, CD8 and TCR in lpr mice. When a whole fraction of mononuclear cells (MNC) in various immune organs of lpr mice was injected into scid mice (allogeneic circumstance), CD8+ TCRint cells mainly expanded. They had a high density of IL-2R beta. This was true when bone marrow cells of lpr mice were injected into scid mice. On the other hand, when MNC of the spleen and bone marrow in lpr mice were injected into irradiated (9 Gy) lpr mice (syngeneic circumstance), the major expanding cells were DN TCRint cells expressing a low density of IL-2R beta. A cell-sorting experiment for purified fractions demonstrated that only CD8- cells reconstituted TCRint cells in scid mice. Namely, DN CD4- CD8- cells as well as CD4+ cells which once acquired the mature phenotype, no longer switched their phenotype. These results suggest that the phenotype of TCRint cells is influenced by the surrounding microenvironment.     

Functional plasticity of the LACK-reactive Vbeta4-Valpha8 CD4(+) T cells normally producing the early IL-4 instructing Th2 cell development and susceptibility to Leishmania major in BALB / c mice

Early production of IL-4 by LACK-reactive Vbeta4-Valpha8 CD4(+) T cells instructs aberrant Th2 cell development and susceptibility to Leishmania major in BALB / c mice. This was demonstrated using Vbeta4(+)-deficient BALB / c mice as a result of chronic infection with MMTV (SIM), a mouse mammary tumor virus expressing a Vbeta4-specific superantigen. The early IL-4 response was absent in these mice which develop a Th1 response to L. major. Here, we studied the functional plasticity of LACK-reactive Vbeta4-Valpha8 CD4(+) T cells using BALB/ c mice inoculated with L. major shortly after infection with MMTV (SIM), i. e. before deletion of Vbeta4(+) cells. These mice fail to produce the early IL-4 response to L. major and instead exhibit an IFN-gamma response that occurs within LACK-reactive Vbeta4-Valpha8 CD4(+) T cells. Neutralization of IFN-gamma restores the production of IL-4 by these cells. These data suggest that the functional properties of LACK-reactive Vbeta4-Valpha8 CD4(+) T cells are not irreversibly fixed.     

Immune-mediated cholangiohepatitis in neonatally thymectomized mice: the role of T cells and analysis of T-cell receptor Vbeta usage

We have previously reported the induction of immune-mediated cholangiohepatitis following injection of a hybrid recombinant proteins containing the E2 of the pyruvate dehydrogenase (PDC-E2) and the branched-chain keto-acid dehydrogenase (BCOADC-E2) to neonatally thymectomized (Tx) A/J mice. Further, we demonstrated that intrahepatic infiltrating mononuclear cells could transfer pathology to other Tx mice. To further our observations, we examined intrahepatic infiltrating mononuclear cells by flow cytometry and used cell transfer experiments to identify the phenotype involved. Interestingly, following immunization of neonatally Tx A/J mice and immunization with the bihybrid molecule, the number of CD3+infiltrating mononuclear cells were significantly higher (77.8%) compared with the control group. There was a small although not significant increase among intrahepatic infiltrating mononuclear cells and splenic cells of Vbeta 5.1,5.2+, Vbeta7+and Vbeta17+. In addition, Vbeta14+cells accounted for 20.4% of the infiltrating T-cells (P<0.01 vs. the control group). In further experiments, CD3+, CD4+or CD8+cells were isolated and removed from intrahepatic infiltrating mononuclear cells and subpopulations of mononuclear cells transferred to Tx mice. Both CD3+CD4+cells and CD3+CD8+cells are required for development of the lesion, and the damage is mediated by CD3+Vbeta14+cells.     

T cell receptor V beta genes expressed by IgG anti-DNA autoantibody-inducing T cells in lupus nephritis: forbidden receptors and double-negative T cells

In the (SWR x NZB)F1 (SNF1) model of lupus nephritis, pathogenic variety of IgG anti-DNA autoantibodies are induced by certain T helper (Th) cells that are either CD4+ or CD4-CD8- (double negative; DN) in phenotype. From the spleens of eight SNF1 mice with lupus nephritis, 149 T cell lines were derived and out of these only 25 lines (approximately 17%) were capable of augmenting the production of pathogenic anti-DNA autoantibodies. Herein, we analyzed the T cell receptor (TcR) V beta genes used by 16 such pathogenic autoantibody-inducing Th cell lines. Twelve of the Th lines were CD4+ and among these five lines expressed V beta 8 (8.2 or 8.3). The V beta 8 gene family is contributed by the NZB parent to the SNF1 mice, since it is absent in the SWR parental strain. Three other CD4+ Th lines expressed V beta 4, another was V beta 2+ and one line with poor autoantibody-inducing capability expressed V beta 1. Four autoantibody-inducing Th lines from the SNF1 mice had a DN phenotype and these lines were also autoreactive, proliferating in response to syngeneic spleen cells. Among these DN Th lines, two expressed V beta 6 and one expressed V beta 8.1 TcR. Both of these are forbidden TcR directed against Mls-1a (Mlsa) autoantigens expressed by the SNF1 mice and such autoreactive T cells should have been deleted during thymic ontogeny. Thus, the DN Th cells of non-lpr SNF1 mice are different from the DN cells or MRL-lpr which lack helper activity and do not express forbidden TcR. The spleens of 6 out of 19 nephritic SNF1 animals tested also showed an expansion of forbidden autoreactive TcR+ cells that were mainly DN. Two of these animals expressed high levels of V beta 6 (anti-Mlsa) and V beta 11 (anti-I-E) TcR+ cells, three others had high levels of V beta 11+ cells alone and one animal had an expanded population of V beta 17a+ (anti-I-E) cells. The I-E-reactive TcR again should have been eliminated in the SNF1 thymus, since they express I-E molecules contributed by the NZB parent. The SWR parents of SNF1, are I-E-; moreover, they lack the V beta 11 gene but they express V beta 17a in peripheral T cells. Whereas the NZB parents are I-E+, they lack a functional V beta 17a gene and they delete mature V beta 11+ T cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

On the role of T lymphocytes in stimulation of humoral immunity induced by peptidoglycan-monomer linked with zinc.

Effects of peptidoglycan linked with zinc (PGM-Zn) were investigated on plaque-forming cell (PFC) generation to sheep red blood cell (SRBC) and SRBC-unrelated antibody production in primary and secondary immune response in mice depleted in vivo of CD4+ and/or CD8+ T lymphocytes. PGM-Zn in nondepleted mice stimulated the PFC generation and IgM or IgG and IgG1 production in primary and secondary reaction. Single depletion of CD4 or CD8+ T cells did not change this ability. The effects of PGM-Zn after CD8+ depletion were even greater than those in nondepleted mice. Depletion of both T cell subsets, however, completely abrogated immunostimulatory effects of PGM on PFC generation (primary and secondary response), as well as on primary SRBC-unrelated antibody production, leaving only the increase of IgG in secondary response unchanged. Immunostimulatory effects and isotype switching to IgG1 and IgG2a correlated with the changes in splenic CD4+, CD8+, CD5+ cells, pointing to the regulatory role of these cells and/or their cytokines in PGM-Zn-induced immunostimulation. Altogether the data suggest that PGM-Zn may potentiate the costimulatory signals coming from activated T cells and act on B cells without the T cell help.     

Genotype-restricted lymphoproliferation in autoimmune lpr mice

Transfer of bone marrow (BM) from autoimmunity-prone mice homozygous for the new lymphoproliferation mutation (lprcg) caused systemic lymphoproliferation in irradiated lprcg/lprcg recipients but not in irradiated +/+ recipient (J. Exp. Med. 1990. 171:519; Eur. J. Immunol. 1991.21: 63). It was thus hypothesized that the lprcg gene expresses its function at lymph nodes (LN) to provide anomalous lprcg/lprcg lymphoid cells with the environment where they can accumulate. This was confirmed by LN transplantation and BM transfer studies. In the LN transplantation study lprcg/lprcg LN grafts with or without in vitro irradiation swelled and lprcg/+ LN grafts were slightly hyperplastic or apparently normal; however, whereas +/+ LN grafts atrophied in lprcg/lprcg recipients, they were all histologically normal in +/+ and lprcg/+ recipients. Irradiation of lprcg/lprcg LN grafts significantly retarded their swelling in lprcg/lprcg recipients. In the BM transfer study lprcg/lprcg BM cells caused systemic lymphoproliferation in lpr/lpr and gld/+, lprcg/+ recipients and sporadic LN swelling in lprcg/+ recipients but LN atrophy in gld/gld recipients. In the study using both techniques in combination, lpr/lpr LN grafts swelled but gld/gld LN grafts atrophied in lprcg/lprcg BM----+/+ chimeras. All the swollen LN contained Thy-1+CD4-CD8 lymphoid cells or "double-negative (DN)" T cells characteristic of the lpr disease. Analysis of DNA restriction fragment length polymorphism demonstrated that lprcg/lprcg DN cells derived from lprcg/lprcg BM cells accumulated in lpr/lpr LN and gld/+, lprcg/+LN. The following conclusions have been drawn: (a) the lprcg gene determines the ability of lprcg/lprcg DN cell to accumulate in LN; (b) this genetic trait is not totally recessive differing from lymphoproliferation; (c) lpr/lpr LN and gld/+, lprcg/+ LN are equivalent to lprcg/lprcg LN in the receptivity of lprcg/lprcg DN cell accumulation thus supporting the allelism of lpr with lprcg and the complementation between gld and lprcg (J. Exp. Med. 1990. 171:519), respectively; (d) the ability of lprcg/lprcg LN to accumulate DN cells is partially resistant to irradiation; (e) lprcg/lprcg DN cells may cause atrophy of gld/gld LN and +/+ LN and (f) the gld and lpr genes are different from each other in the phenotype expressed at the LN site.     

Differential reactivity of TCR Vβ10 alleles to a mouse mammary tumor virus superantigen

Mouse mammary tumor virus (MMTV) expresses a superantigen (SAg) which plays a critical role in the viral life cycle. We have recently described the new infectious MMTV (SIM) encoding a Vβ4-specific SAg in mice with a TCR-Vβ^b haplotype. We have now compared the SAg activity of this virus in BALB / c mice harboring the TCR-Vβ^a, TCR-Vβ^b or TCR-Vβ^c haplotypes which differ by a central deletion in the TCR-Vβ^a and TCR-Vβ^c locus and by mutations in some of the remaining Vβ elements. Injection of MMTV (SIM) led to a strong stimulation of Vβ4 + CD4 + T cells in TCR-Vβ^b mice, but only to a weak stimulation of these cells in TCR-Vβ^a or TCR-Vβ^c mice. A large increase in the percentage of Vβ10 + cells was observed among CD4 + T cells in mice with the Vβ ^a or Vβ ^c, but not the Vβ ^b TCR-Vβ haplotype. Vβ 10+ cells dominated the response when Vβ10^a/c and Vβ 4 subsets were present together. This is the first report of a viral SAg interacting with murine Vβ10 + cells. Six amino acid differences between Vβ10^{a / c} and Vβ10^b could account for the gain of reactivity of Vβ10^{a / c} to the MMTV(SIM) SAg. No mutations were found in the hypervariable region 4 (HV4) of the TCR. Mutations at positions 22 and 28 introduce into Vβ10^{a / c} the same amino acids which are found at these positions in the MMTV(SIM)-reactive Vβ4. Tridimensional models indicated that these amino acids lie close to HV4 and are likely to be important for the interaction of the SAg with the TCR.     

Reversal of the abnormal development of T cell subpopulations in the thymus of autoimmune MRL-lpr/lpr mice by a polyamine biosynthesis inhibitor.

Polyamines--putrescine, spermidine, and spermine--are a group of positively charged organic molecules that are present in all living cells. They are important regulators of cell growth and differentiation, but the precise mechanism of their action is not known. Ornithine decarboxylase (ODC) is a key enzyme in the biosynthesis of polyamines. Recent studies demonstrated that down-regulation of polyamine biosynthesis by irreversible inhibition of ODC with difluoromethylornithine (DFMO0 is a novel therapeutic approach for the treatment of murine lupus in autoimmune MRL-lpr/lpr mice. Since murine lupus in this strain is associated with a major alteration in thymic T cell subopulations, we questioned whether abnormal polyamine biosynthesis contributes to aberrant T cell maturation in the thymus of MRL-lpr/lpr mice. Thymocytes were analyzed for cell surface markers, CD4 and CD8 by 2-color flow cytometry using their respective monoclonal antibodies. The proportion of thymocyte subsets in disease-free mice (8-10 week of age) was approximately 72% double positive (DP; CD4+CD8+) cells, 5-7% double negative (DN; CD4-CD8-) cells, 11-16% CD4+ cells and 7-8% CD8+ cells. At 14 weeks of age, a stage of clinical disease expression, thymocytes were marked by the presence of approximately 40% DN cells and approximately 25% DP cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Factors controlling levels of CD8+ T-cell lymphocytosis associated with murine gamma-herpesvirus infection.

Intranasal infection of mice with murine gamma-herpesvirus 68 (MHV-68) elicits a striking CD8+ T-cell lymphocytosis following the establishment of latency, which includes a marked increased frequency of Vbeta4+ CD8+ T cells. The Vbeta4+ CD8+ T cells do not recognize a conventional viral peptide, but are stimulated by an uncharacterized ligand expressed on latently infected, activated B cells. The selective expansion of Vbeta4+ CD8+ T cells after MHV-68 infection is observed in all mouse strains examined, although the fold-increase varies widely, ranging from less than twofold to greater than 10-fold. The factors controlling the variation are currently undefined. In the current study, CD8+ T cell activation and Vbeta4+ CD8+ T-cell frequencies were analyzed in 18 inbred strains of mice. The data show that the magnitude of the Vbeta4+ CD8+ T-cell response correlates with the degree of CD8+ T cell-activation, and that both major histocompatibility complex (MHC) and non-MHC genes contribute to the magnitude of the activation. Furthermore, the magnitude of the response does not reflect major differences in susceptibility to viral infection and/or corresponding differences in the acute response. Rather the degree of Vbeta4+ CD8+ T cell activation may be determined by differences in levels of expression of the stimulatory ligand at the peak of latency.     

A Vβ4-specific superantigen encoded by a new exogenous mouse mammary tumor virus

The superantigen (SAg) expressed by mouse mammary tumor virus (MMTV) has been shown to play an essential role in the course of the viral life cycle. In the present study, we describe a Vβ4-specific SAg encoded by a new exogenous MMTV carried by the SIM mouse strain. This is the first report of a viral or bacterial SAg reacting with mouse Vβ4⁺ T cells. Injection of MMTV(SIM) into adult BALB/c mice leads to a rapid and strong stimulation of Vβ4⁺ CD4⁺ T cells, followed by a slow deletion of these cells. Neonatal exposure to the virus also leads to a progressive deletion of Vβ4⁺ T cells. In contrast to other strong MMTV SAg, this new SAg requires the presence of major histocompatibility complex class II I-E molecules to be presented efficiently to T cells. Sequence analysis revealed a new predicted amino acid sequence in the C-terminal polymorphic region of this SAg. Furthermore, sequence comparisons to the most closely related SAg with different Vβ specificities hint at the specific residues involved in the interaction with the T cell receptor.     

Non-exclusive Fas control and age dependence of viral superantigen-induced clonal deletion in lupus-prone mice

To investigate the role of Fas in the induction of tolerance by viral superantigen (SAG), we infected MRL-+/+ and MRL-lpr (Fas mutant) mice with mouse mammary tumor virus (MMTV) (SW), a virus encoding an SAG with the same specificity as endogenous Mtv-7-SAG. In normal mice, this infection has two distinct consequences on specific Vβ6⁺CD4⁺ T cells, consisting of activation followed by clonal deletion. MMTV (SW)-SAG-induced activation in vivo was identical in MRL-+/+ and MRL-lpr mice. In contrast, clonal deletion showed age-dependent impairment. Early infection (5 weeks) led to identical clonal deletion of specific T cells in blood lymphocytes from MRL-+/+ and MRL-lpr mice, although clonal deletion was slightly impaired in the MRL-lpr lymph nodes. Late infection (10 weeks) of MRL-lpr mice led to markedly delayed and reduced clonal deletion. Vβ6⁺CD4⁺ T cells which escaped clonal deletion in aging MRL-lpr mice were not anergized by interaction with SAG. These results show that peripheral clonal deletion induced by viral SAG in adult mice is controlled by Fas, but not exclusively so.