Overlap of the anti-Sm and anti-DNA responses of MRL/Mp-lpr/lpr mice

Autoantibodies specific for the Sm ribonucleoprotein are spontaneously produced in patients with SLE and in mice of the MRL mouse strains. We have previously reported the characterization of the clonality and V region gene use of 41 MRL/Mp-lpr/lpr (MRL/lpr)-derived B cell hybridomas selected for Sm binding. In this report, we show that many of the expressed V genes of these hybridomas are also expressed by anti-DNA hybridomas of MRL/lpr mice. Moreover, the anti-Sm hybridomas from nine clonal groups produce antibodies that bind ssDNA, and those of five clones produce antibodies that also bind dsDNA. Sm/DNA-specific hybridomas, but not Sm-only-specific hybridomas, have a higher than expected content of arginine residues in CDR3 of the H chain, similar to MRL/lpr hybridomas selected on the basis of DNA binding. One clone displays intraclonal differences in DNA binding, inasmuch as the most extensively mutated members produce antibodies that are able to bind dsDNA and have a higher affinity for ssDNA than the least mutated members of this clone. Thus, DNA appears to be a selecting Ag in this response. These data indicate an overlap in the anti-Sm and anti-DNA autoimmune responses in MRL mice that may have implications for the activation of anti-Sm B cells, and for defining the spectrum of Ag targeted in SLE.

V region gene analysis of anti-Sm hybridomas from MRL/Mp-lpr/lpr mice

Anti-Sm autoantibodies are unique to SLE, but are present in only 25% of patients with this disease. This response also occurs at a similar frequency in mice of the autoimmune MRL strains. Previous analyses of the anti-Sm response in these mice indicate that its occurrence is controlled by stochastic events, and suggest that Sm is the driving Ag. To further elucidate the role of Ag in this response, and to test the hypothesis that the 25% incidence is due to a requirement for particular Ig gene rearrangements or somatic mutations, we have analyzed the specificity and V-region gene sequences of 41 anti-Sm B cell hybridomas derived from nine anti-Sm-positive MRL/Mp-lpr/lpr mice. The majority of hybridomas are specific for the D peptide of the Sm particle. Hybridomas of independent origin express unique VH/V kappa combinations with diverse junctional sequences and are variable in the extent of somatic mutation. Thus, the response does not appear to be dependent upon the occurrence of a rare Ig gene rearrangement or specific somatic mutation. The response exhibits restriction in JH and VH gene use, and in individual mice is oligoclonal, suggestive of Ag selection. In the few B cells for which mutations can be identified, the evidence for selection of mutant B lymphocytes, based on patterns of mutation, is ambiguous. However, there is remarkably little intraclonal diversity, suggesting that the overall mutation rates in these clones are low.

Overlap of the anti-Sm and anti-DNA responses of MRL/Mp-lpr/lpr mice

Autoantibodies specific for the Sm ribonucleoprotein are spontaneously produced in patients with SLE and in mice of the MRL mouse strains. We have previously reported the characterization of the clonality and V region gene use of 41 MRL/Mp-lpr/lpr (MRL/lpr)-derived B cell hybridomas selected for Sm binding. In this report, we show that many of the expressed V genes of these hybridomas are also expressed by anti-DNA hybridomas of MRL/lpr mice. Moreover, the anti-Sm hybridomas from nine clonal groups produce antibodies that bind ssDNA, and those of five clones produce antibodies that also bind dsDNA. Sm/DNA-specific hybridomas, but not Sm-only-specific hybridomas, have a higher than expected content of arginine residues in CDR3 of the H chain, similar to MRL/lpr hybridomas selected on the basis of DNA binding. One clone displays intraclonal differences in DNA binding, inasmuch as the most extensively mutated members produce antibodies that are able to bind dsDNA and have a higher affinity for ssDNA than the least mutated members of this clone. Thus, DNA appears to be a selecting Ag in this response. These data indicate an overlap in the anti-Sm and anti-DNA autoimmune responses in MRL mice that may have implications for the activation of anti-Sm B cells, and for defining the spectrum of Ag targeted in SLE.

V region gene analysis of anti-Sm hybridomas from MRL/Mp-lpr/lpr mice

Anti-Sm autoantibodies are unique to SLE, but are present in only 25% of patients with this disease. This response also occurs at a similar frequency in mice of the autoimmune MRL strains. Previous analyses of the anti-Sm response in these mice indicate that its occurrence is controlled by stochastic events, and suggest that Sm is the driving Ag. To further elucidate the role of Ag in this response, and to test the hypothesis that the 25% incidence is due to a requirement for particular Ig gene rearrangements or somatic mutations, we have analyzed the specificity and V-region gene sequences of 41 anti-Sm B cell hybridomas derived from nine anti-Sm-positive MRL/Mp-lpr/lpr mice. The majority of hybridomas are specific for the D peptide of the Sm particle. Hybridomas of independent origin express unique VH/V kappa combinations with diverse junctional sequences and are variable in the extent of somatic mutation. Thus, the response does not appear to be dependent upon the occurrence of a rare Ig gene rearrangement or specific somatic mutation. The response exhibits restriction in JH and VH gene use, and in individual mice is oligoclonal, suggestive of Ag selection. In the few B cells for which mutations can be identified, the evidence for selection of mutant B lymphocytes, based on patterns of mutation, is ambiguous. However, there is remarkably little intraclonal diversity, suggesting that the overall mutation rates in these clones are low.

Aberrant expression of the very early activation antigen on MRL/Mp-lpr/lpr lymphocytes

MRL/Mp-lpr/lpr (MRL/lpr) mice develop marked lymphadenopathy, characterized predominantly by Thy1+CD3+CD4-CD8- cells ("double negative T cells"; DNT). It is paradoxical that DNT proliferate poorly in vitro when stimulated through CD3 or by mitogens. The hamster mAb H1.2F3, raised against dendritic epidermal DNT, recognizes a very early activation (VEA) Ag, which is generally absent on resting cells but expressed soon after T cell activation with ConA or phorbol ester. Cross-linking of this disulfide-linked dimer in the presence of APC and phorbol ester induces proliferation of normal T cells. Therefore, we tested to see whether MRL/lpr DNT expressed this Ag and whether it might play a role in DNT expansion. Unmanipulated cells from enlarged MRL/lpr lymph nodes expressed VEA in an age-dependent manner, peaking at 3 to 4 mo of age. Only limited expression in a small subset of lymphocytes from the congenic MRL/Mp(-)+/+ strain was seen. VEA expression on freshly harvested MRL/lpr lymphocytes was seen mainly on DNT, yet double staining of the DNT for VEA Ag and three other markers known to be present on lpr DNT showed that the DNT were a heterogeneous population. In addition, some CD4+ T cells expressed VEA Ag. Despite their constitutive VEA Ag expression, MRL/lpr DNT showed no proliferative response to cross-linking with the H1.2F3 antibody. Furthermore, unlike normal T cells, they failed to respond to the antibody even when phorbol ester was added. The addition of supplementary cytokines did not correct this defect. These studies indicate that MRL/lpr DNT constitutively and aberrantly express VEA but do not respond when it is cross-linked. These abnormalities may result from the failure to express Fas, the recently reported apoptosis-inducing receptor defective in lpr mice.

Aberrant expression of the very early activation antigen on MRL/Mp-lpr/lpr lymphocytes

MRL/Mp-lpr/lpr (MRL/lpr) mice develop marked lymphadenopathy, characterized predominantly by Thy1+CD3+CD4-CD8- cells ("double negative T cells"; DNT). It is paradoxical that DNT proliferate poorly in vitro when stimulated through CD3 or by mitogens. The hamster mAb H1.2F3, raised against dendritic epidermal DNT, recognizes a very early activation (VEA) Ag, which is generally absent on resting cells but expressed soon after T cell activation with ConA or phorbol ester. Cross-linking of this disulfide-linked dimer in the presence of APC and phorbol ester induces proliferation of normal T cells. Therefore, we tested to see whether MRL/lpr DNT expressed this Ag and whether it might play a role in DNT expansion. Unmanipulated cells from enlarged MRL/lpr lymph nodes expressed VEA in an age-dependent manner, peaking at 3 to 4 mo of age. Only limited expression in a small subset of lymphocytes from the congenic MRL/Mp(-)+/+ strain was seen. VEA expression on freshly harvested MRL/lpr lymphocytes was seen mainly on DNT, yet double staining of the DNT for VEA Ag and three other markers known to be present on lpr DNT showed that the DNT were a heterogeneous population. In addition, some CD4+ T cells expressed VEA Ag. Despite their constitutive VEA Ag expression, MRL/lpr DNT showed no proliferative response to cross-linking with the H1.2F3 antibody. Furthermore, unlike normal T cells, they failed to respond to the antibody even when phorbol ester was added. The addition of supplementary cytokines did not correct this defect. These studies indicate that MRL/lpr DNT constitutively and aberrantly express VEA but do not respond when it is cross-linked. These abnormalities may result from the failure to express Fas, the recently reported apoptosis-inducing receptor defective in lpr mice.

Conventional B cells, not B-1 cells, are responsible for producing autoantibodies in lpr mice

Mice homozygous for the lpr gene develop autoantibodies and polyclonal B cell activation similar to what is seen in human systemic lupus erythematosus patients. We have previously shown that an lpr-specific intrinsic B cell defect was necessary for autoantibody production in this model. In the current study, we have further defined these autoantibody-producing B cells. Two major subsets of B cells have been described. B-1 cells (CD5+ B cells) can be distinguished from conventional B cells on the basis of phenotype, cytokine secretion, gene expression, anatomical location, and function. In addition, B-1 cells have been implicated in autoimmunity in several murine and human studies. To address the question of which B cell subset produces autoantibodies in lpr mice, we used immunoglobulin heavy chain (Igh) allotype-marked peritoneal (B-1 cell source) and bone marrow (conventional B cell source) cells from lpr mice to establish B cell chimeras. We used two general approaches. In one, we reconstituted sublethally irradiated mice with B-1 cells of one allotype and bone marrow cells of another allotype. In the second method, we suppressed endogenous B cells in neonatal mice with allotype-specific anti-IgM antibody, and injected peritoneal cells of another allotype. After antibody treatment was stopped, the mouse's conventional B cells recovered, but the B-1 subset was only reconstituted by the donor. In both types of chimeras, antichromatin, rheumatoid factor, and anti-single stranded DNA (ssDNA) autoantibodies were produced by the conventional B cell bone marrow source. In addition, an age-related decrease in peritoneal B-1 cells was seen, even in unmanipulated lpr mice. These data show that lpr B-1 cells are not important producers of autoantibodies. Conventional B cells are the source of autoantibodies directed at chromatin, ssDNA, and IgG.

T- and B-cell abnormalities in systemic lupus

A wealth of T- and B-cell abnormalities has been described in systemic lupus erythematosus (SLE). In general, T and B cells manifest evidence of intense in vivo activation, yet perform poorly when tested for in vitro responsiveness to exogenous antigen. The immune system behaves as if its commitment to self-responsiveness overrides the normal capacity to respond to immunogenic challenges. Many immunoregulatory abnormalities have been characterized, but their relation to disease remains controversial. Although a widely accepted unifying hypothesis for the vigorous autoantibody production and associated immune deficiency of SLE is lacking, it seems certain that the profound abnormalities of T and B cells in SLE are intertwined with the fundamental cause of this illness.

Auditory projections to the anterior telencephalon in the budgerigar (Melopsittacus undulatus)

The connections of a higher order auditory area in the neostriatum intermedium pars ventrolateralis (NIVL) were mapped with pathway tracing techniques in order to elucidate possible pathways by which auditory feedback may influence vocal learning in the budgerigar (Melopsittacus undulatus). Previous research has shown that NIVL receives projections from Field 'L' as well as adjacent portions of the dorsolateral neostriatum intermedium (NIDL) and hyperstriatum ventrale (HV) and, therefore, may be homologous to previously described auditory centers in the dorsal and lateral portions of the auditory neostriatum of songbirds. The efferent connections of NIVL terminate within a small portion of the rostromedial archistriatum as well as a more rostrally situated area within the medial neostriatum intermedium (NI) and HV. Near by (but not overlapping) fields in NI and HV receive input from the nucleus dorsomedialis posterior thalami (DMP), the archistriatum and ectostriatum. Interestingly, only the DMP projection field overlaps a neural field known to be related to the vocal motor system. The DMP projection field corresponds to that previously described as the magnocellular nucleus of the anterior neostriatum; this nucleus is known to project to the higher vocal center in the budgerigar. In addition to projections from NIVL to medial NI and HIV, auditory information is relayed to the anterolateral telencephalon directly from the brainstem via the ventrolateral nucleus of the lateral lemniscus (VLV). This latter pathway appears comparable to that described in pigeons derived from the intermediate nucleus of the lateral lemniscus. The projection field of VLV overlaps a restricted portion of the caudal and medial aspect of nucleus basalis. These results support the notion that many aspects of telencephalic auditory pathways in birds are primitive characters, although a direct connection between auditory and vocal motor circuits was not found in the present study.

Influence of the Ig H chain locus on autoantibody production in autoimmune mice

Autoimmune disease is influenced by multiple genes. In this study, we investigated the role of one genetic locus, Ig H chain. IgG2a antichromatin, anti-ssDNA, and antihistone autoantibodies (autoAb) from (MRL/Mp-lpr/lpr x C57BL/6-lpr/lpr), (Ighj/b); (C57BL/6-lpr/lpr x C57BL/6-lpr/lpr-Igha), (Ighb/a); and (MRL/Mp-lpr/lpr x MRL/Mp-lpr/lpr-Ighb), (Ighj/b) mice were determined using allotype-specific ELISA. Strikingly, antichromatin and antihistone antibodies (Ab) were comprised of significantly more b allotype than either a or j allotype in all cohorts of F1 mice examined. In mice that produced anti-Sm Ab, the b allotype was used preferentially for these autoAb as well. However, no allotype skewing was observed in IgG2a Ab directed against TNP or DNA, or for total IgG2a. An Igh recombinant locus was utilized to examine the genetic control of b allotype skewing in lpr mice and in chronic graft vs host disease. In both models, the VH region did not appear to be responsible for the preferential use of b allotype. These results indicate a contribution to autoimmunity by the Igh locus and raise the possibility that Ig allotype may influence autoimmune disease by its effect on the production of certain autoAb.

Influence of the Ig H chain locus on autoantibody production in autoimmune mice

Autoimmune disease is influenced by multiple genes. In this study, we investigated the role of one genetic locus, Ig H chain. IgG2a antichromatin, anti-ssDNA, and antihistone autoantibodies (autoAb) from (MRL/Mp-lpr/lpr x C57BL/6-lpr/lpr), (Ighj/b); (C57BL/6-lpr/lpr x C57BL/6-lpr/lpr-Igha), (Ighb/a); and (MRL/Mp-lpr/lpr x MRL/Mp-lpr/lpr-Ighb), (Ighj/b) mice were determined using allotype-specific ELISA. Strikingly, antichromatin and antihistone antibodies (Ab) were comprised of significantly more b allotype than either a or j allotype in all cohorts of F1 mice examined. In mice that produced anti-Sm Ab, the b allotype was used preferentially for these autoAb as well. However, no allotype skewing was observed in IgG2a Ab directed against TNP or DNA, or for total IgG2a. An Igh recombinant locus was utilized to examine the genetic control of b allotype skewing in lpr mice and in chronic graft vs host disease. In both models, the VH region did not appear to be responsible for the preferential use of b allotype. These results indicate a contribution to autoimmunity by the Igh locus and raise the possibility that Ig allotype may influence autoimmune disease by its effect on the production of certain autoAb.

The lpr and gld genes in systemic autoimmunity: life and death in the Fas lane

The single gene lpr and gld models of spontaneous systemic autoimmunity have attracted much attention in recent years. Here, Philip Cohen and Robert Eisenberg describe the fascinating recent findings that the lpr and gld [corrected] phenotypes result from defects in the Fas gene and, perhaps, in the ligand for fas, respectively.

The murine Sm-D autoantigen: multiple genes, genetic polymorphism, evolutionary conservation and lack of intervening sequences in the coding region

Antibodies to the Sm nuclear antigen are diagnostic of systemic lupus erythematosus (SLE). MRL/Mp-lpr/lpr mice develop a similar illness, and a proportion also develop anti-Sm. To understand better anti-Sm reactivity in this murine model, we have cloned the murine Sm-D autoantigen. One cDNA clone was 517 bp long with an open reading frame of 357 nucleotides, encoding a 13.3 kDa protein of 119 amino acids. At the nucleotide level, the murine Sm-D cDNA was 89.8% homologous with human Sm-D (94% in the coding region), yet there was identity at the protein level, including a Gly-Arg nine-fold repeated C-terminus motif. Southern blot analysis of PstI-digested genomic DNA from seven mouse strains demonstrated a 7.8 kb band in every strain; in addition, a 2.8 kb band was seen in AKR/J, LG/J and MRL/Mp-lpr/lpr. PCR amplification of genomic DNA showed a single Sm-D gene product of 360 bp, which indicated a lack of intervening sequences. The Sm-D protein is thus highly conserved in evolution, probably owing to its essential role in the physiology of the cell.

Tetraparental mice reveal complex cellular interactions of the mutant, autoimmunity-inducing lpr gene

Lpr is a murine recessive autosomal mutant gene that, in conjunction with the background genes of different inbred mouse strains, produces varied syndromes of lymphadenopathy and autoantibody production. We have investigated the cellular basis of the lpr determined phenomena by constructing allophenic (tetraparental) chimeras of MRL/Mp-lpr/lpr combined with C57BL/6 and MRL/+ combined with C57BL/6-lpr/lpr. The appearance of lymphadenopathy, lpr atypical T cells, and autoantibodies was found to depend on the relative amounts +/+ and lpr tissue. The failure of these three abnormalities to correlate in certain animals suggested different pathways of lpr gene action. Furthermore, in the lpr predominant animals, both the lymphadenopathy and autoantibodies were essentially entirely contributed by the lpr donor. The expression of the lpr gene within the same cells expressing the MRL or B6 background determined the pathologic and serologic manifestations characteristic of the disease of that lpr strain, despite the presence of +/+ cells of the other background in the same individual. The lpr syndrome thus depends on the intracellular interaction of the lpr and background genes, and on positive signalling between different lpr cell populations.

Tetraparental mice reveal complex cellular interactions of the mutant, autoimmunity-inducing lpr gene

Lpr is a murine recessive autosomal mutant gene that, in conjunction with the background genes of different inbred mouse strains, produces varied syndromes of lymphadenopathy and autoantibody production. We have investigated the cellular basis of the lpr determined phenomena by constructing allophenic (tetraparental) chimeras of MRL/Mp-lpr/lpr combined with C57BL/6 and MRL/+ combined with C57BL/6-lpr/lpr. The appearance of lymphadenopathy, lpr atypical T cells, and autoantibodies was found to depend on the relative amounts +/+ and lpr tissue. The failure of these three abnormalities to correlate in certain animals suggested different pathways of lpr gene action. Furthermore, in the lpr predominant animals, both the lymphadenopathy and autoantibodies were essentially entirely contributed by the lpr donor. The expression of the lpr gene within the same cells expressing the MRL or B6 background determined the pathologic and serologic manifestations characteristic of the disease of that lpr strain, despite the presence of +/+ cells of the other background in the same individual. The lpr syndrome thus depends on the intracellular interaction of the lpr and background genes, and on positive signalling between different lpr cell populations.

Clonal analysis of peripheral T cell precursors in lpr mice

MRL/Mp-lpr/lpr mice develop massive lymphadenopathy characterized by expansion of an unusual population of T cells with the Thy 1+, CD3+, CD4-, CD8- (double negative) phenotype. The role these cells play in accelerating the autoimmune syndrome seen in these mice is unknown. In order to better understand the origin of the expanded population of T cells, we have derived a panel hybridomas from double negative lpr lymph node cells. Surprisingly, eleven of twelve hybridomas selected for the absence of surface CD4 and CD8 do not express CD3. Six of eleven confirmed to have inherited the MRL T cell receptor locus have rearrangement at that locus, suggesting commitment to a T cell lineage. Only hybridoma 2.4, which expresses CD3, responds to ConA, anti-CD3 monoclonal antibody, and induces antibody production. The presence of CD3-, CD4-, CD8- T cells in the periphery of lpr mice confirms aberrant T cell development in these mice and suggests an intrinsic cell defect which is expressed early in lymphopoiesis.

CD3 expression, modulation and signalling in T-cell subpopulations from MRL/Mp-lpr/lpr mice

The expanded T-cell population of MRL/Mp-lpr2lpr mice is abnormal from a variety of standpoints. We have already shown that T-cell receptor expression and modulation are aberrant in the predominant CD4- CD8 (DN) T cell population. To investigate these abnormalities further, we examined CD3 expression and modulation in subpopulations of +/+ and lpr T cells and measured mitogen-induced Ca++ mobilization in DN lpr T cells. We found that expression and modulation of CD3 in CD4hi and CD8hi lpr single positive (SP) T cells are similar to that in +/+ T cells. We have, however, identified additional lpr cell subsets that are CD4lo or CD8lo. Their expression and modulation of CD3 are intermediate, between that of SP and DN lpr T cells. These subpopulations may thus represent a transitional stage between the SP and DN populations. The rapid modulation of CD3 in the DN population does not appear to be merely related to the lack of expression of CD4 or CD8, and may in fact cause (rather than result from) low CD3 expression. In addition, we observed impairment of CA++ mobilization in DN lpr T cells in response to concanavalin A or anti-CD3 antibody. These findings further define the abnormalities of T cells from lpr mice.

An intrinsic B cell defect is required for the production of autoantibodies in the lpr model of murine systemic autoimmunity

Mice homozygous for the gene lpr develop marked lymphadenopathy and a spectrum of autoantibodies closely resembling that of human systemic lupus erythematosus. The unusual T cell phenotype of the expanded lymphocyte population and the T-dependence of several antibodies in this strain have suggested that primary T cell abnormalities underlie the autoimmune syndrome. Using double chimeras, we now show that expression of the lpr gene in B cells is absolutely necessary for autoantibody production. Combinations of anti-Thy 1.2 + C' treated bone marrow from congenic strains of C57BL/6 mice, differing only at the immunoglobulin heavy chain (Igh) and lpr loci, were transferred into lethally irradiated B6/lpr mice. Double chimerism was documented by allotype-specific surface IgD and IgM immunofluorescence assay of peripheral blood and by allotype-specific enzyme-linked immunosorbent assay for total IgM in serum. Despite the presence of both +/+ and lpr B cells, IgM and IgG2a anti-chromatin as well as IgM anti-IgG were entirely the products of lpr B cells. Total serum IgG2a and IgG1 were also dominated by the lpr phenotype but not to the same extent. A similar experiment using B6/lpr-Igha recipients confirmed these findings. Additional experiments in which B6/lpr recipients were infused with ratios of donor bone marrow favoring B6.C20 +/+ over B6/lpr showed that even though +/+ B cells were overrepresented, autoantibodies were only of the lpr allotype. In addition, in the presence of lpr B cells, normal B cells showed little response to an exogenous, T cell-dependent antigen. The data thus indicate that lpr B cells manifest an intrinsic abnormality which is essential for autoantibody production in the lpr model.

Targeting of T-B interaction using heteroconjugate antibody

We have deliberately targeted collaboration between T cells and certain B cells by using a heteroconjugate (HETCONJ) antibody. This specific reagent was created by cross-linking the F(ab')2 portions of anti-I-Ab and anti-CD3 monoclonal antibodies. Spleen cells from B6 (I-Ab) but not bm12 (I-Abm12) mice proliferated in vitro in the presence of the HETCONJ. Similarly, T-cell dependent IgM secretion was induced in B cells from B6, yet only weakly in B cells from bm 12 mice. Using B cells from Igh allotype double congenic (B6.C20 Igha/I-Ab and bm12, Ighb/I-Abm12) mice in co-culture experiments, we have used the HETCONJ to study linked versus bystander T-B interaction. B-cell activation, mediated by HETCONJ, was 10 times greater in unseparated than in resting splenic B cells. T-B interaction through T-B contact was more efficient than activation through bystander effects both for unseparated and resting splenic B cells. Large, already activated B cells, in contrast, did not show a preference for linked recognition. Our reagent has mimicked some of the events involved in T-B collaboration and may be useful in studying the molecular basis of cellular interactions.

Lpr and gld: single gene models of systemic autoimmunity and lymphoproliferative disease

The autosomal recessive lpr and gld genes induce in mice multiple autoantibodies and the progressive accumulation of large numbers of non-malignant CD4- CD8- T lymphocytes. The clinical syndromes and immune abnormalities associated with these two nonallelic genes are nearly identical and are also highly dependent on background genes. MRL/lpr mice are particularly severely affected, and they develop a syndrome that is serologically and pathologically similar to human systemic lupus erythematosus (SLE). Abnormal cell marker expression in the aberrant lpr T lymphocytes includes surface antigens normally associated with activated T cells or even with B cells, and it occurs along with enhanced expression of certain oncogenes. The lpr gene results in intrinsic abnormalities of both T and B lymphocytes, yet its location and product are unknown. The gld gene is located on chromosome 1; its product is also unknown. Although many immunological abnormalities are known, the mechanism whereby these two genes induce autoimmunity and lymphoproliferation remains obscure. Further studies of mice bearing these mutant genes are certain to yield insights into systemic autoimmunity and the control of lymphocyte proliferation.

Lymphomas of the breast. A clinicopathologic and immunohistochemical study of primary and secondary cases

Primary mammary lymphoma is rare, and little is known about the immunophenotype of such cases. The authors studied both primary and secondary breast lymphomas with a broad panel of T- and B-cell markers using paraffin-embedded tissue and the avidin-biotin immunoperoxidase method. Cases of primary B-cell lymphoma were further tested to determine light and heavy chain type. Thirty-five cases were analyzed, including 16 primary lymphomas. Diffuse large cell lymphoma was present in ten of 16 primary and 14 of 18 secondary cases. Lymphoepithelial lesions in ducts and lobules and frequent vascular involvement were found in both primary and secondary cases. Immunohistochemistry studies on 13 tumors revealed all of the primary tumors to be B-cell in origin, except for one case of primary T-cell lymphoma; to the authors' knowledge, this represents the first description of this entity. Fifteen of 17 secondary tumors exhibited B-cell markers and one of 17 exhibited T-cell markers; in only one case could lineage not be determined. Among primary B-cell cases, IgM was found to be the most frequent heavy chain type; IgA reactivity was found in only one case. Survival was related to stage and histologic characteristics; patients with Stage II disease and higher grade histologic lesions had a worse prognosis. Half of the patients with primary lymphoma have had recurrent disease. Although local recurrences were observed, the authors also saw a tendency for recurrence in other extranodal sites. The authors conclude that, although primary lymphoma of the breast is compatible with long-term survival, a significant number of patients eventually die of their disease. As with other extranodal lymphomas, survival rate appears most related to stage of disease. Also, the vast majority of primary tumors are B-cell in origin, express IgM heavy chain, and can be considered tumors of mucosa-associated lymphoid tissue.

Experimental induction of systemic lupus erythematosus by recognition of foreign Ia

A chronic GVH reaction induced in normal mice results in a syndrome that closely resembles SLE. In this study, we compared the autoimmune GVH syndrome induced in parent (C57BL/6Kh [B6] and B6.C-H-2bm12 [bm12]) and F1 [( B6 x bm12]F1) mice by transfer of parental spleen cells. A majority of the mice in all groups developed autoantibodies to chromatin and erythrocytes, and some of the mice also produced anti-dsDNA antibodies. The predominant isotype of the anti-chromatin autoantibodies was found to be IgG2a, although high levels of IgG2b antibodies were also present. Autoantibody production was in general more intense and more prevalent in parent----F1 hybrid combinations, compared to parent----parent infusions. No influence of host or graft gender was observed. These studies show that a chronic GVH reaction can be induced by both parent----parent and parent----hybrid combinations.

Autoantibodies in chronic graft versus host result from cognate T-B interactions

A chronic graft-versus-host reaction (GVH) induced in nonautoimmune mice causes a syndrome that closely resembles SLE. In this model, donor T cells react against incompatible host Ia structures and generate excessive help, which activates a subpopulation of self-reactive B cells. We have studied whether these self-reactive B cells are activated by direct interaction with alloreactive T cells or by nonspecific bystander effects. Two types of chimeras were made: double-parental chimeras, differing at both Ia and Igh allotype [B6.C20 + bm12----(B6.C20 x bm12)F1]; and control chimeras [(B6.C20 x bm12)F1----(B6.C20 x bm12)F1]. A chronic GVH syndrome was induced in the chimeras by infusion of B6 or bm12 spleen cells. Coombs and antichromatin autoantibodies were measured using Igh allotype-specific immunoassays. The double-parental chimeras that received bm12 cells made autoantibodies principally of the Igha allotype, indicating that the bm12 T cells interacted only with the Iab-bearing host B cells. Conversely, double-parental chimeras that received B6 cells made mostly Ighb autoantibodies, indicating direct cognate interaction with the Iabm12-bearing host B cells. The control chimeras made autoantibodies of both allotypes. These results indicate that autoantibodies in chronic GVH result from direct T-B interactions and not from nonspecific T cell-derived factors.

Allotype-specific immunoregulation of autoantibody production by host B cells in chronic graft-versus host disease

A chronic graft-vs-host (GVH) reaction induced in nonautoimmune mice by the transfer of Ia-incompatible spleen cells results in a syndrome that closely resembles SLE in the spectrum of autoantibodies and immunopathology. We have utilized Ia- and Igh-congenic strains to study the immunoregulation of autoantibody-producing B cells in this model. We have found that the autoantibodies are produced almost entirely by the host B cells. The transferred donor B cells contributed neither to the autoimmune response nor to the total serum Ig, with rare exceptions. The donor cell population did, however, exert an Igh allotype-specific immunoregulatory effect on the host B cells. For example, in allotype-heterozygous recipients, the autoantibodies were preferentially made by those host cells that expressed the donor allotype, whereas those host B cells that expressed nondonor allotype were relatively suppressed. In allotype-homozygous recipients, the donor cells frequently suppressed the host IgG2a allotype completely. This suppression sometimes prevented the IgG antichromatin response, although in other cases the response occurred with the use of a different isotype. In a final set of experiments, a chronic GVH reaction was induced in which both the donors and the recipients were Igh allotype heterozygous and yet differed at Ia. In this case, no donor influence on allotype should be expected; yet the IgG2a autoantibodies were clearly skewed toward the b allotype. These results show that host B cells play a unique role in the GVH autoimmune syndrome. In addition, they are immunoregulated in allotype-specific manners, some of which presumably involve interaction with donor T cells.