Constitutive activation of the Fas ligand gene in mouse lymphoproliferative disorders.

Mice homozygous for lpr (lymphoproliferation) or gld (generalized lymphoproliferative disease) develop lymphadenopathy and splenomegaly and suffer from autoimmune disease. The lpr mice have a defect in a cell-surface receptor, Fas, that mediates apoptosis, while gld mice have a mutation in the Fas ligand (FasL). Northern hybridization with the FasL cDNA as probe indicated that the cells accumulating in lpr and gld mice abundantly express the FasL mRNA without stimulation. By means of in situ hybridization and immunohistochemistry, we identified the cells expressing the FasL mRNA as CD4-CD8- double negative T cells. The T cells from lpr mice were specifically cytotoxic against Fas-expressing cells. Since FasL is normally expressed in activated mature T cells these results indicate that the double negative T cells accumulating in lpr and gld mice are activated once, and support the notion that the Fas/FasL system is involved in activation-induced suicide of T cells. Furthermore, the graft-versus host disease caused by transfer of lpr bone marrow to wild-type mice can be explained by the constitutive expression of the FasL in lpr-derived T cells.     

Evidence for early onset, polyclonal activation of T cell subsets in mice homozygous for lpr.

Mice homozygous for lpr and gld develop profound lymphadenopathy characterized by the accumulation of two functionally anergic T cell subsets, a predominant B220+CD4-CD8- double negative (DN) population and a minor, closely related CD4 dull+ B220+ population. Lymph nodes from diseased lpr and gld mice also contain abnormally high numbers of conventional T cells, and we reported recently that a high proportion of lpr and gld CD4+B220- T cells have the hallmarks of primed or memory T cells. In the present study, we further investigated the extent, ontogeny, and possible causes of T cell activation in lpr and gld mice. The criteria used to identify primed or memory T cells included activation-dependent increases in the expression of CD44, LFA-1, and the early activation Ag, CD69, and decreases in the expression of Mel-14 and CD45RB, as well as quantitative differences in the in vitro production of IFN-gamma and the TNF-alpha by stimulated cells. A comparison of TCR V beta gene utilization by lpr T cell subsets also was undertaken. The results showed that T cell activation was widespread and complex. CD8+ T cells exhibited a similar pattern of activation to CD4+B220- T cells. The activation of these two subsets occurred in parallel, was in evidence by 4 to 6 wk of age, and was both chronic and progressive. The proportions of CD44hiLFA-1hi, CD4+B220-, and CD8+ T cells increased steadily between 4 and 20 wk of age, but changes in T cell growth, Mel-14, and CD45RB expression and cytokine secretion were not observed until mice were older than 11 wk. A very different pattern of activation was observed for B220+ T cells. At all ages, B220+ DN and CD4+B220+ T cells were CD44hiMel-14hi and 60 to 75% were CD69+. The expression of CD69 appeared to be stimulus dependent rather than constitutive, suggesting that these cells, too, may be chronically stimulated in vivo. In keeping with their anergic state, DN T cells responded poorly to cross-linking of CD69. The stimuli inducing chronic activation of CD4+B220- and CD8+ T cells are unlikely to include inappropriate reactions to autoantigens because there was no evidence for selective accumulation of CD4+ or CD8+ T cells bearing particular V beta genes or potentially self-reactive cells that normally are deleted in the thymus. By comparison, C3H-lpr DN cells displayed some potentially significant differences in V beta 6 and V beta 9 expression from CD4+B220- and CD8+ T cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Abundant expression of type l K+ channels. A marker for lymphoproliferative diseases?

Using the patch clamp whole-cell recording technique, we studied expression of K+ channels in mAb-defined T cell subsets from diseased C3H-lpr/lpr and C3H-gld/gld mice and from healthy C3H-HeJ congenic controls. Both mutant mouse strains develop a lupus-like syndrome accompanied by hyperplasia of a functionally and phenotypically abnormal T cell subset. These defective cells, which are Thy-1.2+ CD4- CD8- B220+ F23.1+, display an abundance of type l K+ channels. Phenotypically similar lymph node T cells from normal C3H-HeJ mice, or young C3H-lpr/lpr mice before the onset of disease, do not display large numbers of type l K+ channels. CD4+ CD8- T cells (helper/inducer) from the mutant mice express a small number of type n K+ channels, and CD4- CD8+ T cells (suppressor/cytotoxic) show a low level of type l or n' K+ channels, as do their phenotypically equivalent counterparts in the normal mouse thymus. These results suggest that the abundant expression of type l K+ channels is a marker for the defective lpr and gld T cell subset and may reflect the "abnormal" proliferative status of these cells.     

Characterization of reciprocal Lmb1-4 interval MRL-Faslpr and C57BL/6-Faslpr congenic mice reveals significant effects from Lmb3

Susceptibility to severe lupus in MRL-Fas(lpr) mice requires not only the lpr mutation but also other predisposing genes. Using (MRL-Fas(lpr) x B6-Fas(lpr))F2 (where B6 represents C57BL/6) intercrosses that utilize the highly susceptible MRL and poorly susceptible B6 backgrounds, we previously mapped CFA-enhanced systemic lupus-like autoimmunity to four loci, named Lmb1-4, on chromosomes 4, 5, 7, and 10. In the current study, we generated and analyzed reciprocal interval congenic mice for susceptibility to CFA-enhanced autoimmunity at all four Lmb loci. Although all loci had at least a slight effect on lymphoproliferation, only Lmb3 demonstrated a major effect on lymphoproliferation and anti-chromatin Ab levels. Further characterization of Lmb3, primarily by comparing MRL-Fas(lpr) with MRL.B6-Lmb3 Fas(lpr) congenic mice, revealed that it also played a significant role in spontaneous lupus, modifying lymphoproliferation, IgG and autoantibody levels, kidney disease, and survival. The less susceptible B6 Lmb3 locus was associated with a marked reduction in numbers of CD4(+) and double-negative (CD4(-)CD8(-)) T cells, particularly in lymph nodes, as well as reduced T cell proliferation and enhanced T cell apoptosis, both in vivo and in vitro. IFN-gamma-producing CD4(+) T cells were also reduced in MRL.B6-Lmb3 Fas(lpr) mice. Further mapping using subinterval congenic mice placed Lmb3 in the telomeric portion of chromosome 7. Thus, Lmb3, primarily through its effects on CD4(+) and double-negative T cells, appears to be a highly penetrant lupus-modifying locus. Identification of the underlying genetic alteration responsible for this quantitative trait locus should provide new insights into lupus-modifying genes.     

Cytokine secretion by C3H-lpr and -gld T cells. Hypersecretion of IFN-gamma and tumor necrosis factor-alpha by stimulated CD4+ T cells.

Mice homozygous for lpr and gld develop profound lymphadenopathy characterized by the expansion of two unusual T cell subsets, a predominant Ly-5(B220)+ CD4- CD8- double negative (DN) population and a minor CD4 dull+ Ly-5(B220)+ population. The mechanisms promoting lymphoproliferation are unknown, but one possibility is a abnormality in the production of cytokines that regulate T cell growth. In the present report, unfractionated LN cells and sorted T cell subsets from C3H-lpr, -gld, and -+/+ mice were compared for spontaneous and induced secretion of a spectrum of lymphokines. In addition, CD4+, CD4 dull+ Ly-5(B220)+, and DN T cells were examined for expression of CD3 epsilon, TCR-alpha/beta heterodimers, Ly-6C, and CD44 and for proliferative responses to immobilized anti-TCR mAb and cofactors. These studies revealed that sorted DN T cells did not secrete IL-3, IL-4, IL-5, IL-6, GM-CSF, TNF-alpha, or IFN-gamma spontaneously or after TCR-alpha/beta cross-linking. In contrast, stimulated unfractionated lpr and gld LN cells proliferated strongly and secreted high levels of IFN-gamma and TNF-alpha and low levels of IL-3, IL-4, and IL-6. Despite a 5- to 10-fold deficit in the frequency of CD4+ and CD8+ T cells, cytokine secretion by lpr and gld LN generally exceeded that of +/+ LN. Comparisons of cytokine secretion by stimulated CD4+ T cells revealed that +/+, lpr, and gld CD4+ Ly-5(B220)- T cells proliferated strongly, but only lpr and gld cells produced significant levels of IFN-gamma. The lpr and gld CD4+ T cells also produced higher levels of TNF-alpha and IL-2 than +/+ cells. In contrast to normal CD4+ T cells, lpr and gld CD4+ Ly-5(B220)+ T cells proliferated weakly and did not secrete TNF-alpha, IL-2, or, in most experiments, IFN-gamma after stimulation. Phenotypic studies of T cell subsets revealed that unstimulated lpr and gld CD4+ Ly-5(B220)- T cells express significantly higher levels of CD44 than +/+ CD4+ T cells. In addition, CD4 dull+ Ly-5(B220)+ cells closely resembled DN T cells in size and expression of TCR-alpha/beta, CD3epsilon, CD44, and Ly-6C. Since elevated CD44 expression is generally associated with T cell activation and only previously activated normal CD4+ T cells produce high levels of IFN-gamma in vitro, our data suggest that lpr and gld CD4+ Ly-5(B220)- T cells contain a higher than normal proportion of primed or memory T cells and thus may be polyclonally activated in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)     

Fas and Fas ligand expressed on cells of the immune system, not on the target tissue, control induction of experimental autoimmune uveitis

The Fas-Fas ligand (FasL) interaction is important for maintaining lymphocyte homeostasis by signaling for activation-induced cell death. Mice homozygous for the lpr or gld mutations do not express functional Fas or FasL, respectively, and spontaneously develop progressive autoimmune symptoms. Recent studies implicated expression of FasL on immunologically privileged tissues in protection from immune-mediated damage. Conversely, tissue expression of Fas may facilitate damage. We evaluated the susceptibility of lpr and gld mice to induction of experimental autoimmune uveitis (EAU), a T cell-mediated autoimmune disease induced with retinal Ags, which targets the neural retina. gld as well as lpr mice immunized with a retinal Ag developed disease of lower incidence and severity than wild-type controls. Delayed hypersensitivity responses were not significantly different among immunized gld, lpr, or wild-type mice, although in vitro Ag-specific lymphocyte responses of the mutant mice were lower. To evaluate whether the diminished ability of gld and lpr mice to develop EAU was due to a defect at the level of the tissue or the immune system, radiation bone marrow chimeras constructed between wild-type and mutant mice were immunized to induce EAU. Mutant recipients of wild-type bone marrow, but not wild-type recipients of mutant bone marrow, developed normal disease scores. These results indicate that normal expression of Fas and of FasL on cells of the immune system is important for EAU expression. Unexpectedly, neither lack of Fas nor lack of FasL on the ocular tissues affected expression of EAU.     

The Nef-mediated AIDS-like disease of CD4C/human immunodeficiency virus transgenic mice is associated with increased Fas/FasL expression on T cells and T-cell death but is not prevented in Fas-, FasL-, tumor necrosis factor receptor 1-, or interleukin-1beta-converting enzyme-deficient or Bcl2-expressing transgenic mice

CD4(+)- and CD8(+)-T-cell death is a frequent immunological dysfunction associated with the development of human AIDS. We studied a murine model of AIDS, the CD4C/HIV transgenic (Tg) mouse model, to assess the importance of the apoptotic pathway in human immunodeficiency virus type 1 (HIV-1) pathogenesis. In these Tg mice, Nef is the major determinant of the disease and is expressed in immature and mature CD4(+) T cells and in cells of the macrophage/myeloid lineage. We report here a novel AIDS-like phenotype: enhanced death, most likely by apoptosis (as assessed by 7-aminoactinomycin D and annexin V/propidium iodide staining), of Tg thymic and peripheral CD4(+) and CD8(+) T cells. The Tg CD4(+) and CD8(+) T cells were also more susceptible to cell death after activation in vitro in mixed lymph node (LN) cultures. However, activation-induced cell death was not higher in Tg than in non-Tg-purified CD4(+) T cells. In addition, expression of Fas and FasL, assessed by flow cytometry, was increased in CD4(+) and CD8(+) T cells from Tg mice compared to that of non-Tg littermates. Despite the enhanced expression of Fas and FasL on Tg CD4(+) and CD8(+) T cells, Fas (lpr/lpr) and FasL (gld/gld) mutant CD4C/HIV Tg mice developed an AIDS-like disease indistinguishable from lpr/+ and gld/+ CD4C/HIV Tg mice, including loss of CD4(+) T cells. Similarly, CD4C/HIV Tg mice homozygous for mutations of two other genes implicated in cell death (interleukin-1beta-converting enzyme [ICE], tumor necrosis factor receptor 1 [TNFR-1]) developed similar AIDS-like disease as their respective heterozygous controls. Moreover, the double-Tg mice from a cross between the Bcl2/Wehi25 and CD4C/HIV Tg mice showed no major protection against disease. These results represent genetic evidence for the dispensable role of Fas, FasL, ICE, and TNFR-1 on the development of both T-cell loss and organ disease of these Tg mice. They also provide compelling evidence on the lack of protection by Bcl2 against Tg CD4(+)-T-cell death. In view of the high resemblance between numerous phenotypes observed in the CD4C/HIV Tg mice and in human AIDS, our findings are likely to be relevant for the human disease.     

Differential control of autoantibodies and lymphoproliferation by Fas ligand expression on CD4+ and CD8+ T cells in vivo.

We have previously shown that the gld autoimmune syndrome is suppressed in lethally irradiated gld mice reconstituted with a mixture of normal and gld bone marrow (BM). Furthermore, in vivo depletion of normal Thy-1+ cells restores lymphoproliferation and autoantibody production in such chimeras, suggesting that T cells bearing Fas ligand are responsible for correcting the gld defect. In this study, mixed-BM chimeras lacking either normal CD4+ (B6CD4KO-B6gld) or normal CD8+ T cells (B6CD8KO-B6gld) were generated to determine the contribution of the normal T cell subsets to disease suppression. Lymphoproliferation was completely suppressed in B6CD4KO-B6gld chimeras but only modestly in B6CD8KO-B6gld chimeras. On the other hand, both types of mixed-BM chimeras had incomplete effects on the suppression of serum autoantibodies when compared with B6gld reconstituted with isologous BM. These results suggest that both T cell subsets provide Fas ligand to suppress immune cells responsible for autoantibody production; however, CD8+ T cells are mainly responsible for preventing lymphoproliferation.     

Evidence for the existence of two parallel differentiation pathways in the thymus of MRL lpr/lpr mice.

MRL mice homozygous for the lpr/lpr gene develop a massive lymphadenopathy caused by the accumulation of CD4-CD8-, Thy-1-positive T cells that express B220. This phenotypically unusual T cell population coexists with normal, B220- T cells in lpr/lpr animals. To investigate the origin and differentiation pathway of B220+ T cells, the expression of a panel of developmentally regulated cell surface markers including TCR, CD4, CD8, Thy-1, and B220 was examined. Thymocytes and peripheral T lymphocytes from lpr/lpr mice were analyzed by four-color flow cytometry. The results showed that both B220+ and B220- thymocytes contained all of CD4-CD8-, CD4+CD8+, and CD4 or CD8 single positive T cell subpopulation in the lpr thymus. Expression of the V beta 11 TCR, measured by flow cytometry and reverse polymerase chain reaction, was demonstrated in lpr thymus. However, the number of T cells expressing V beta 11 was greatly reduced in both the B220+ and B220- T cell populations in lymph node, spleen, and liver. Taken together, the data provide evidence for maturation and selection of a distinct population of B220+ T cells in the thymus of MRL lpr/lpr mice.     

Lymphocytes from autoimmune MRL lpr/lpr mice are hyperresponsive to IL-18 and overexpress the IL-18 receptor accessory chain

MRL lpr/lpr mice spontaneously develop a severe autoimmune lupus syndrome characterized by strong autoantibody production and massive lymphoproliferation, in which IFN-gamma plays a major pathogenic effect. The role of the IFN-gamma-inducing cytokine IL-18 in the autoimmune syndrome of lpr/lpr mice has been investigated. In response to IL-18, lymph node cells of lpr/lpr mice produce significant amounts of IFN-gamma and proliferate more potently as compared with cells from +/+ mice. Cells likely responsible for such hyperresponsiveness to IL-18 include NK cells and the CD4(+)/CD8(+) self-reactive T lymphocytes characteristically present in lymph nodes of lpr/lpr mice. Analysis of the expression of IL-18R complex revealed that mRNA for the IL-18R alpha-chain is constitutively expressed at similar level both in +/+ and lpr/lpr lymphocytes. In contrast, the expression of the accessory receptor chain IL-18R beta is low in unstimulated +/+ cells but significantly high in lpr/lpr cells. Thus, the abnormally high expression of the IL-18R chain IL-18R beta could be one of the causes of the hyperresponsiveness of lpr/lpr cells to IL-18 at the basis of consequent enhancement of IFN-gamma production and development of IFN-gamma-dependent autoimmune pathology.     

Characterization of lymphoproliferation induced by interactions between lprcg and gld genes.

The lprcg gene is the novel mutation at the lpr locus characterized by its complementary to the gld gene in induction of lymphoproliferation in the mouse. Because of the potential usefulness of mice with this mutation in studies on the interrelationship between lpr and gld, we were urged to characterize the lymphoproliferative disease developing in (CBA/K1Jms-lprcg/lprcg x C3H/HeJ-gld/gld) F1 hybrid (lprcg-gld) mice. Despite the milder lymphadenopathy in the lprcg-gld mice, the expanding lymph node cells showed the same surface marker pattern as that in C3H/HeJ-lpr/lpr, C3H/HeJ-gld/gld, and CBA/K1Jms-lprcg/lprcg mice, characterized by the positivity for Thy-1, B220, Ly-6, and Ly-24, and the negativity for L3T4, Lyt-2 (hence designated double-negative cells), and sIg. Furthermore, these cells proved to be of a T-cell lineage based on the rearrangement of the TCR beta-chain gene, the same as the already known double-negative cells. Noticeably, in lprcg-gld mice, serum IgG and autoantibodies of the IgG class were not elevated at an early age but were slightly elevated at an advanced age despite early elevation of the serum IgM and IgM autoantibodies. These results suggest that the lymphoproliferative mice carrying lprcg and gld genes in a heterozygous state will serve as a new tool for inquiring into the interrelationship among lpr, gld, and lprcg.     

Age Associated Changes in the Distribution of Ipr Gene-Induced B220-Positive T Cells in Lymphoid Organs of MRL/Mp-Ipr/Ipr Mice Using Dual Exposure Microphotographs of Double Immunofluorescence Staining

Homozygous MRL/Mp-1pr/1pr (MRL/1pr) mice, which have an autosomal recessive mutant 1pr gene and exhibit defects in Fas antigen, spontaneously develop autoimmune disease with progressive expansion and accumulation of characteristic abnormal CD4-CD8-double negative T cells that express B220 surface antigen, a B cell-specific surface marker in normal mice. We analyzed the distribution and age related changes of lpr gene-induced abnormal T cells (B220-positive lpr T cells) In the lymphoid organs of MRL/1pr mice. We studied cryostat sections of the spleen, peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches at different stages using FITC (fluorescein isothiocyanate)-conjugated monoclonal antibodies directed against B220 (RA3-6B2) and PE (phycoerythrin)-conjugated anti-mouse CD3 (2C11) monoclonal antibody, examining dual-exposure microphotographs of double-immunofluorescence stained preparations. We observed that in aged MRL/lpr mice, B220-positive abnormal 1pr T cells were not present in the thymus-dependent area, and the majority of the follicular area cells were displaced by 1pr T cells. These findings suggest that the cellular trafficking of B220-positive lpr T cells differs from that of conventional T cells and that these 1pr-derived T cells play a role in the follicle.     

Unique cell surface phenotypes of proliferating lymphocytes in mice homozygous for lpr and gld mutations, defined by monoclonal antibodies to MRL/Mp-lpr/lpr T cells

In mice bearing the autosomal recessive gene of either lpr or gld, generalized T-cell proliferation and autoimmunity occurs. The surface antigen profiles of these proliferating cells were analyzed using two-color flow cytometry analysis with two newly established rat monoclonal antibodies (ALP-1, ALP-2) directed to lpr cells. The Lp-1 antigen, defined by ALP-1, is expressed exclusively on approximately one-half of proliferating lpr and gld lymph node cells. The Lp-2 antigen, like B 220, is expressed on 80-90% of lpr and gld lymph node cells, the cells in B-cell lineage and a small population of Ly-2+ T cells from normal mice. Thus, the lpr and gld lymph node cells were classified into three subsets, Lp-1+/Lp-2+, Lp-1-/Lp-2+ and Lp-1-/Lp-2-. After stimulation with Con A or a combination of IL-2 and phorbol ester, a small population of T cells from normal mice became Lp-1+. The same treatment increased Lp-2+/Ly-2+ and induced Lp-2+/L3T4+ T-cell populations. Therefore, it seems likely that these phenotypically unique T cells are generated at some stage during the proliferation and differentiation of certain normal T-cell subpopulations. The aberrant T cells in mice with lpr and gld mutations may even be normal regulatory T cells, if they are not proliferating abnormally.     

CD2 expression correlates with proliferative capacity of alpha beta + or gamma delta + CD4-CD8- T cells in lpr mice.

The T lymphocytes that accumulate in vast numbers in the lymphoid tissues of lpr/lpr (lpr) mice express a TCR-alpha beta that is polyclonally rearranged, and yet is devoid of surface CD4 or CD8 (CD4-8-) as well as CD2. lpr CD2- alpha beta + CD4-8- T cells exhibit an apparent block in signal transduction, in that when activated they produce little or no IL-2 and proliferate minimally in the absence of exogenous IL-2. In contrast to the predominant hyporesponsive alpha beta + CD4-8- T cells, we observe that a minor subset (1 to 2%) of lpr lymph node CD4-8- cells expresses a TCR-gamma delta and can proliferate upon activation with PMA and ionomycin in the absence of exogenous IL-2. Furthermore, these responsive gamma delta T cells express surface CD2. The functional and phenotypic distinctions of lpr gamma delta T cells led us to identify an analogous minor (4 to 10%) subset of alpha beta + CD4-8- cells in lpr thymus and lymph nodes that does express CD2. Similar to the gamma delta subset, these CD2+ alpha beta + CD4-8- cells are also capable of proliferation and IL-2 production. Thus the capacity for IL-2 production and proliferation by a small proportion of lpr CD4-8- T cells, either alpha beta + or gamma delta +, correlates with their expression of surface CD2. This correlation is supported by the observation that the lpr liver contains actively cycling alpha beta + CD4-8- lymphocytes that are strikingly enriched for CD2 expression. Consequently, unlike the vast proportion of abnormal lpr CD2- CD3+ CD4-8- cells, the CD2+ CD3+ CD4-8- T cells may not express the basic lpr defect, or else are not affected by its presence. These studies suggest that expression of the lpr abnormality may be restricted to a particular T cell lineage. This functional correlation with CD2 expression may be more broadly applicable to phenotypically similar subsets of normal thymocytes, and possibly peripheral tolerized T lymphocytes.     

Age Associated Changes in the Distribution of Ipr Gene-Induced B220-Positive T Cells in Lymphoid Organs of MRL/Mp-Ipr/Ipr Mice Using Dual Exposure Microphotographs of Double Immunofluorescence Staining

Homozygous MRL/Mp-1pr/1pr (MRL/1pr) mice, which have an autosomal recessive mutant 1pr gene and exhibit defects in Fas antigen, spontaneously develop autoimmune disease with progressive expansion and accumulation of characteristic abnormal CD4-CD8-double negative T cells that express B220 surface antigen, a B cell-specific surface marker in normal mice. We analyzed the distribution and age related changes of lpr gene-induced abnormal T cells (B220-positive lpr T cells) In the lymphoid organs of MRL/1pr mice. We studied cryostat sections of the spleen, peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches at different stages using FITC (fluorescein isothiocyanate)-conjugated monoclonal antibodies directed against B220 (RA3-6B2) and PE (phycoerythrin)-conjugated anti-mouse CD3 (2C11) monoclonal antibody, examining dual-exposure microphotographs of double-immunofluorescence stained preparations. We observed that in aged MRL/lpr mice, B220-positive abnormal 1pr T cells were not present in the thymus-dependent area, and the majority of the follicular area cells were displaced by 1pr T cells. These findings suggest that the cellular trafficking of B220-positive lpr T cells differs from that of conventional T cells and that these 1pr-derived T cells play a role in the follicle.     

T-cell mediated suppression in the MRL mouse

MRL/lpr mice possess an autosomal recessive gene, lpr, which is associated with lymphoproliferation and acceleration of autoimmune disease. Lymphoproliferation has been ascribed to a single gene defect predominantly affecting the T-lymphocyte component of the immune system. MRL/++ mice do not possess the lpr autosomal recessive mutation and do not develop early lymphadenopathy. T-lymphocyte functional activity was studied in these mice using the polyclonal T-cell mitogens PHA and Con A. Our results indicated a significant suppression of the spleen and lymph node response of MRL/lpr mice to these polyclonal mitogens as compared to the MRL/++ response noted as early as 6 weeks of age. In addition, there was a progressive decline in the MRL/lpr spleen and lymph node cell mitogenic responses with increasing age. Spleen and lymph node cells from 20-week MRL/lpr mice were also relatively unresponsive in the mixed lymphocyte culture reaction as compared to cells from MRL/ ++ or BALB/c mice. The in vitro proliferative response of the MRL mice was further examined with respect to possible accessory cell modulation by both macrophages and T cells. It was found that in 20-week MRL/lpr lymph nodes a significant degree of suppression of lymphocyte proliferation could be mediated by the MRL/lpr T cell. Increased lymphocyte proliferation to a mitogenic signal could only be demonstrated in those MRL/lpr mice 3 weeks of age.     

IL-7-dependent homeostatic proliferation in the presence of a large number of T cells in gld mice

In gld mice, CD4 and 8-double-negative (DN) T cells as well as naive and memory-phenotype T cells accumulate in the peripheral lymphoid organs. Although Fas ligand (L) defect accounts for the progressive accumulation of abnormal DN T cells, the existence of other mechanisms which may be involved in the defective homeostasis in gld mice has been unclear. In this study, we analyze T-cell homeostasis in gld mice using adoptive transfer systems. It was shown that a gld, but not C57BL/6 (B6), environment led to augmented proliferation of B6 T cells transferred without up-regulation of CD69. Thus, the augmented T-cell proliferation seemed to result from mal-homeostatic proliferation even in the presence of a large number of recipient T cells. T cells from lpr mice showed no significant proliferation in the B6 environment, suggesting that the absence of Fas-Fas L interaction was not responsible for the mal-homeostatic proliferation. Although similar levels of IL-7 mRNA were detected in gld and B6 spleens, the intensity of CD127 and the proportion of CD127+ cells in the T cells were significantly lower in gld mice than in B6 mice, suggesting that IL-7 excess in a gld environment is responsible for the abnormal proliferation of transferred T cells. The administration of anti-CD127 antibody inhibited the proliferation of transferred lymphocytes. Thus, IL-7-dependent proliferation seems to be involved in the abnormal proliferation of lymphocytes in gld recipients.     

Functional analysis of T cell subsets from mice bearing the lpr gene

The autosomal recessive lpr (lymphoproliferation) gene is responsible for a thymus-dependent massive lymphoproliferation associated with the development of lupus-like autoimmune disease. Phenotypic analysis of adult lpr/lpr lymph nodes has demonstrated accumulation of a dull Lyt-1+, Thy-1+ population that expresses neither Lyt-2 nor L3T4 antigens. With the use of a depletion method based on complement-mediated lysis with an anti-Lyt-2 monoclonal antibody (31 M) and a new anti-L3T4 monoclonal antibody (RL 172.4), we have purified the Lyt-2- L3T4- subset from lymph nodes or spleens of C57BL/6-lpr/lpr mice and determined whether they are immunologically functional in vitro. Production of neither interleukin 2 nor interferon-gamma was detected by the double-negative subset after stimulation with concanavalin A and/or phorbol myristate acetate. The frequencies of allospecific cytotoxic T lymphocyte (CTL) precursors and lectin-induced antigen-nonspecific CTL precursors were diminished to almost undetectable levels, whereas the Lyt-2+ population from lpr/lpr mice had CTL-precursor frequencies comparable with that of +/+ mice. These results show that the major cell subset of adult lpr/lpr lymph nodes or spleens is composed of lymphocytes with markedly limited potential for lymphokine production or antigenic stimulation.