Interleukin 2 responses of lpr and normal L3T4-/Lyt-2- T cells induced by TPA plus A23187

The major population of cells that accumulate abnormally in MRL/Mp-lpr/lpr lymphoid tissue is Thy-1+, L3T4-, and Lyt-2-. To clarify the functional potential of these cells, we examined their proliferation, interleukin 2 (IL 2) receptor expression, and IL 2 secretion by using as stimulants the combination of 12-O-tetradecanoylphorbol-2-acetate and A23187 (a calcium ionophore). Although the lpr T cells were capable of responding to these stimulants, the nature of the response and of the concentrations of ligand required differed sharply from the responses of normal adult T cells, and of adult L3T4-Lyt-2- thymocytes. There was a strong similarity but not identity when responses of 16 day fetal thymocytes were compared with those of lpr L3T4-Lyt-2- cells. The unusual functional properties of the lpr cells, such as high A23187 dose requirement for maximal proliferation, low percentage of IL 2 receptor-expressing cells, and low levels of IL 2 secretion, suggested that these cells are arrested at a stage of development similar to that of 16-day fetal thymocytes and before adult L3T4-/Lyt-2- thymocytes.

Characterization of functional T-cell lines derived from MRL mice

In an effort to characterize further the role of T cells in the autoimmune disease of MRL/Mp-lpr/lpr (lpr) mice, continuous cell lines were established from spleen and lymph nodes using EL-4 lymphoma supernatants as a source of T-cell growth factor(s). Five lines were derived from lpr spleen and lymph nodes, and an equal number from MRL/Mp- +/+ (+/+). All of the lines lost their alloreactivity after a short time in culture. Surprisingly, every line manifested marked proliferation in response to autologous irradiated spleen cells. This response was restricted to I-Ak, as it was blocked with monoclonal anti-I-Ak antibodies, and as B10.A(4R) accessory cells were stimulatory while B10.A(3R) were not. There was no difference in the degree of stimulation from lpr accessory cells compared to that in those from +/+ or other H-2k mice. The T-cell lines bore Thy-1, Ly-1, L3T4, and 7D4 (interleukin 2 (IL-2) receptor), but lacked Ly-2 and surface Ig. They proliferated in response to both conventional and recombinant DNA-derived IL-2. When cocultured with Ia-identical B cells, the T-cell lines provoked B-cell division and antibody production. The cells also caused intense proliferation when cultured with freshly isolated lpr (but not +/+) lymph node cells. The results indicate that lpr lymphoid tissue contains functional T cells reactive to autologous Ia molecules and capable of inducing both B-cell activation and the proliferation of lpr lymphocytes. Such cells may be of importance in inducing hypergammaglobulinemia, autoantibody production, and lymphoproliferation in these SLE mice.

Role of the Sm antigen in the generation of anti-Sm autoantibodies in the SLE-prone MRL mouse

MRL/Mp-+/+ (+/+) and MRL/Mp-lpr/lpr (lpr) mice spontaneously produce the SLE-specific anti-nuclear antibody, anti-Sm. Previous work on the clonality and specificity of the anti-Sm response has suggested that the Sm antigen itself induces this autoantibody. In the present work, we have directly investigated the immunogenicity of Sm. In short-term cultures, Sm antigen was shown to be important for the de novo generation of anti-Sm PFC in vitro. The addition of purified Sm to cultures of spleen cells from anti-Sm-positive lpr mice augmented the number of anti-Sm PFC on day 4. Also, the addition of Fab anti-Sm to such cultures inhibited the generation of anti-Sm PFC, probably by blocking determinants on endogenous Sm. The ability of the autoantigen to initiate anti-Sm generation in vivo was investigated by hyperimmunizing +/+ mice with Sm from rabbit or mouse sources. Such mice specifically produced antibodies that recognized both rabbit and mouse Sm as determined by ELISA. The IgG subclass distribution of these induced antibodies was similar to that of spontaneous anti-Sm antibodies found in older mice of the same strain. Our data indicate that the Sm antigen can both initiate and augment production of the anti-Sm autoantibody. These findings provide additional evidence that the spontaneous anti-Sm response in SLE is antigen driven.

Role of the Sm antigen in the generation of anti-Sm autoantibodies in the SLE-prone MRL mouse

MRL/Mp-+/+ (+/+) and MRL/Mp-lpr/lpr (lpr) mice spontaneously produce the SLE-specific anti-nuclear antibody, anti-Sm. Previous work on the clonality and specificity of the anti-Sm response has suggested that the Sm antigen itself induces this autoantibody. In the present work, we have directly investigated the immunogenicity of Sm. In short-term cultures, Sm antigen was shown to be important for the de novo generation of anti-Sm PFC in vitro. The addition of purified Sm to cultures of spleen cells from anti-Sm-positive lpr mice augmented the number of anti-Sm PFC on day 4. Also, the addition of Fab anti-Sm to such cultures inhibited the generation of anti-Sm PFC, probably by blocking determinants on endogenous Sm. The ability of the autoantigen to initiate anti-Sm generation in vivo was investigated by hyperimmunizing +/+ mice with Sm from rabbit or mouse sources. Such mice specifically produced antibodies that recognized both rabbit and mouse Sm as determined by ELISA. The IgG subclass distribution of these induced antibodies was similar to that of spontaneous anti-Sm antibodies found in older mice of the same strain. Our data indicate that the Sm antigen can both initiate and augment production of the anti-Sm autoantibody. These findings provide additional evidence that the spontaneous anti-Sm response in SLE is antigen driven.

Anti-Sm autoantibodies in MRL mice: analysis of precursor frequency

Individual MRL-lpr mice vary in their capacity to generate anti-Sm autoantibodies spontaneously. We have compared the frequency of B-cell precursors for this autoantibody in serologically negative and serologically positive MRL-lpr mice, and in normals. Anti-Sm precursors were present in a frequency of approximately 1 per 10-30,000 in spleen cell cultures from anti-Sm positive mice, but were undetectable when spleen cells from serologically negative MRL-lpr mice or from normal mice were examined. Despite LPS stimulation, neither IgM nor IgG precursors could be detected. In parallel cultures, in contrast, anti-DNA autoantibody precursors were readily detected. The results thus indicate that, for the lupus-specific autoantibodies, the absence of antibody in autoimmune mice reflects a deficit in precursor B lymphocytes rather than an active regulatory mechanism. It is suggested that the generation of anti-Sm may reflect a low-probability random event in the generation of B-cell diversity.

Spontaneous antiidiotypic antibodies to the NZB Coombs autoantibody

We have further investigated the phenomenon of spontaneous anti-(Coombs) antiidiotypic antibodies in the F1 hybrids of New Zealand black (NZB) and CBA mice. These mice show an age-related increase in incidence of such antiidiotype during the first year of life. There is no difference between males and females in the occurrence of antiidiotype. Reciprocal hybrids are both affected, so that maternal influence from the NZB strain is not critical. The antiidiotype also occurs in spite of the xid gene. We have so far detected such spontaneous antiidiotype only in (CBA X NZB)F1 hybrids and not in hybrids of NZB with two other strains or in a variety of recombinant inbred strains between NZB and C58. Our results to data suggest extensive shared idiotypy among NZB mice and a limited number of total idiotypes.

Alu RNA-protein complexes formed in vitro react with a novel lupus autoantibody

We have screened sera from patients with systemic lupus erythematosus for reactivity with RNA transcribed in vitro using HeLa whole cell extracts. Sera from 14 out of 114 patients precipitated an RNA transcribed by RNA polymerase III from a plasmid containing an Alu family sequence (i.e. the repetitive DNA sequence that is cut by the Alu restriction enzyme) located upstream from the human gamma G-globin gene. These Alu transcripts were not precipitated by anti-La, anti-Sm, anti-RNP or anti-Ro antibodies, suggesting that Alu RNA was precipitated by a previously undescribed lupus specificity. Analysis of [35S]methionine-labeled immunoprecipitates indicated that Alu RNA binds a protein of about 68 kDa. This protein may be Alu specific since three different Alu transcripts were precipitated by the anti-Alu sera whereas another RNA polymerase III transcript, adenovirus VA I RNA, was not precipitated by the same sera.

Antinuclear antibodies and nuclear antigens in NZB myeloma ascitic fluids

Approximately 5-10% of ascitic fluids from 411 NZB myeloma tumors were found to possess either antinuclear (ANA) or Coombs antibodies. Some fluids showed anti-SM specificity, which is thought to be unique to systemic lupus erythematosus (SLE). In addition, the ascitic fluids were found to contain large amounts of DNA and Sm autoantigens. Further passage of ANA-positive myelomas indicated that the autoantibodies were not products of the myeloma cells themselves. The sporadic appearance of unsuspected autoantibodies in ascitic fluids may cause confusion when working with myeloma or with hybridoma reagents. Furthermore, the development of SLE-specific anti-Sm antibodies in this context suggests parallels between myeloma development and autoimmunity.

H-2-linked Ir gene control of T cell recognition of the Sm nuclear autoantigen and the aberrant response of autoimmune MRL/Mp-+/+ mice

We have examined T cell recognition of the nuclear autoantigen Sm. Rabbit Sm-primed cells from autoimmune MRL/Mp-+/+ (+/+) mice and from all normal strains tested were able to proliferate to rabbit Sm in vitro. In contrast, the reactivity of normal strains to Sm of murine origin was genetically restricted; only H-2f strains B10.M and A.CA, and H-2s strains B10.S and A.SW could recognize mouse Sm, suggesting that responsiveness to mouse Sm was under the control of H-2-linked Ir genes. Although five Iak-bearing normal strains (B10.A, B10.A(2R), B10.BR, A/Sn, and CBA) did not recognize mouse Sm, autoimmune +/+ (Iak) mice were responders. The responsiveness of the +/+ mice to Sm was probably not due to differences in their Iak region, compared with other strains, because the Iak region of normal strains and the autoimmune +/+ strain were indistinguishable by interstrain MLC, immune response gene product function, and recognition by anti-Iak mAb. Inhibition of Sm-induced proliferation by mAb demonstrated that T cells from autoimmune +/+ mice, responder normal strains, and nonresponder normal strains recognized rabbit and mouse Sm in the context of I region-encoded products. The T cell response to Sm antigen in normal mice is therefore Ia region restricted and, for the murine antigen, under Ir gene control. Autoimmune mice that spontaneously make anti-Sm antibodies (+/+) also perceive Sm in an Ia-restricted manner, but their responder status abrogates H-2-linked Ir gene control.

Hidden autoantibodies against common serum proteins in murine systemic lupus erythematosus. Detection by in vitro plaque-forming cell assay

The autoantibodies found in human and murine systemic lupus erythematosus (SLE) are generally directed against cells or components of cells such as nuclear antigens. This predilection may be due to the unusual immunogenicity of certain autoantigens, or to unusual patterns of antibody crossreactivity. Alternatively, the observed spectrum of reactivities may reflect the in vivo absorption of those autoantibodies directed against soluble antigens. To test whether hitherto undetected autoantibodies against serum proteins might exist in murine SLE, we developed assays that were independent of the possibility of absorption of autoantibodies by serum autoantigens; large numbers of plaque-forming cells (PFC) directed against mouse albumin and mouse transferrin were easily detected in the spleens of MRL/Mp-lpr/lpr, BXSB, and NZB mice. The secreted antibodies were relatively specific for the mouse proteins, since only limited cross-reactivity was seen with albumin and transferrins of other species in inhibition experiments. The production of these hidden antibodies could not be the result of diffuse polyclonal B cell activation, since the PFC to mouse transferrins and albumin were not always accompanied by comparable numbers of PFC against related albumins and transferrins. The results indicate that autoantibody production in murine lupus is a generalized phenomenon, not limited to the production of autoantibodies to nuclear or other cell-bound antibodies. However, the relative specificity of the autoantibodies for self-antigens indicates that diffuse polyclonal B cell activation cannot be the mechanism responsible, and argues that a selective mechanism, probably driven by antigen, accounts for production of autoantibodies in SLE.

H-2-linked Ir gene control of T cell recognition of the Sm nuclear autoantigen and the aberrant response of autoimmune MRL/Mp-+/+ mice

We have examined T cell recognition of the nuclear autoantigen Sm. Rabbit Sm-primed cells from autoimmune MRL/Mp-+/+ (+/+) mice and from all normal strains tested were able to proliferate to rabbit Sm in vitro. In contrast, the reactivity of normal strains to Sm of murine origin was genetically restricted; only H-2f strains B10.M and A.CA, and H-2s strains B10.S and A.SW could recognize mouse Sm, suggesting that responsiveness to mouse Sm was under the control of H-2-linked Ir genes. Although five Iak-bearing normal strains (B10.A, B10.A(2R), B10.BR, A/Sn, and CBA) did not recognize mouse Sm, autoimmune +/+ (Iak) mice were responders. The responsiveness of the +/+ mice to Sm was probably not due to differences in their Iak region, compared with other strains, because the Iak region of normal strains and the autoimmune +/+ strain were indistinguishable by interstrain MLC, immune response gene product function, and recognition by anti-Iak mAb. Inhibition of Sm-induced proliferation by mAb demonstrated that T cells from autoimmune +/+ mice, responder normal strains, and nonresponder normal strains recognized rabbit and mouse Sm in the context of I region-encoded products. The T cell response to Sm antigen in normal mice is therefore Ia region restricted and, for the murine antigen, under Ir gene control. Autoimmune mice that spontaneously make anti-Sm antibodies (+/+) also perceive Sm in an Ia-restricted manner, but their responder status abrogates H-2-linked Ir gene control.

Response of MRL/Mp-+/+ mice to mouse Sm: non-H-2-linked genes determine T cell recognition

In normal mouse strains, the T cell proliferative response to the nuclear autoantigen Sm is under MHC-linked Ir gene control. Autoimmune MRL/Mp-+/+ (+/+) mice, which spontaneously make anti-Sm antibodies, have the nonresponder H-2k MHC genotype, yet their T cells respond to mouse Sm. In the present study, we have used Sm-reactive continuous T cell lines to show that the Sm responsiveness of +/+ T cells is not due to aberrancy of the Iak molecules expressed on +/+ antigen-presenting cells. Additionally, the failure of normal Iak mouse strains to respond to mouse Sm could not be attributed to the influence of suppressor cells. Therefore, the response of +/+ mice to mouse Sm is probably due to the development of an abnormal repertoire of T cells capable of recognizing self-antigens in the context of Ia. Analyses of F1 hybrid and backcross mice indicated that their responsiveness was inherited in a dominant manner, probably as a single gene not linked to H-2. Further investigation of this gene and its mode of action may lead to increased understanding of the mechanisms of spontaneous autoimmunity in SLE mice.

Quantitation of the Sm nuclear antigen in tissues and activated lymphocytes

Anti-Sm antibodies are specific for the diagnosis of systemic lupus erythematosus both in humans and in mice. Because the autoantibody response to this nuclear ribonucleoprotein particle is probably antigen driven, we have quantitated the Sm antigen in cells and tissues, using a highly sensitive and specific enzyme-linked immunosorbent assay. The Sm content of several in vitro cell lines was determined to be approximately 1 pg of Sm/cell. We found that murine spleen cells stimulated in vitro with either T cell or B cell mitogens contained up to 10 times more Sm than did unstimulated cells and that they also released increased amounts of Sm. In a survey of organs from several mouse strains, we found that lymphoid tissues had the largest amounts of Sm and that the Sm content of a particular tissue correlated with its DNA content. Increased amounts of Sm in and around activated lymphocytes, as found in systemic lupus erythematosus, may provide a source of antigen for the induction of the anti-Sm autoantibody.

Subset specificity of antilymphocyte antibodies in systemic lupus erythematosus. Preferential reactivity with cells bearing the T4 and autologous erythrocyte receptor phenotypes

The relative specificity of systemic lupus erythematosus antilymphocyte antibodies for T cell subsets bearing the OKT4, OKT8, or autologous erythrocyte rosette (A-RFC) markers was examined in complement-dependent microcytotoxicity assays and by indirect immunofluorescence. Target cells included normal OKT4+ or OKT8+ T cell clones established from mitogen-activated blasts, resting or phytohemagglutinin-activated peripheral T cells highly enriched for OKT4+ cells or OKT8+ cells, and A-RFC+ and A-RFC- populations. In the majority of sera, cytotoxicity for T4+ cells was greater than that for T8+ cells regardless of cellular activation status. Overall cytotoxicity was considerably higher for activated cells, however, especially when warm assay temperatures were used. A-RFC+ targets were more reactive than nonrosetting T cells, and this was associated with strikingly higher relative fluorescence intensity of IgM staining. Despite these consistent differences in relative cytotoxicity or staining, antibody titers against all cell types were strongly correlated in individual sera. Absorption experiments failed to demonstrate distinct antibody specificities for T4+ and A-RFC+ cells. These data suggest that the major determinant of cytotoxic reactivity may be a single or limited number of surface antigens common to all T cells. Superimposed on this dominant system(s) is a special reactivity with certain distinct subsets and with activated T cells generally.

Response of MRL/Mp-+/+ mice to mouse Sm: non-H-2-linked genes determine T cell recognition

In normal mouse strains, the T cell proliferative response to the nuclear autoantigen Sm is under MHC-linked Ir gene control. Autoimmune MRL/Mp-+/+ (+/+) mice, which spontaneously make anti-Sm antibodies, have the nonresponder H-2k MHC genotype, yet their T cells respond to mouse Sm. In the present study, we have used Sm-reactive continuous T cell lines to show that the Sm responsiveness of +/+ T cells is not due to aberrancy of the Iak molecules expressed on +/+ antigen-presenting cells. Additionally, the failure of normal Iak mouse strains to respond to mouse Sm could not be attributed to the influence of suppressor cells. Therefore, the response of +/+ mice to mouse Sm is probably due to the development of an abnormal repertoire of T cells capable of recognizing self-antigens in the context of Ia. Analyses of F1 hybrid and backcross mice indicated that their responsiveness was inherited in a dominant manner, probably as a single gene not linked to H-2. Further investigation of this gene and its mode of action may lead to increased understanding of the mechanisms of spontaneous autoimmunity in SLE mice.

Unusual acidic light chains in murine SLE serum

The sera of autoimmune and other mouse strains were analysed by high resolution two dimensional gel electrophoresis and silver staining. The most striking finding was the presence of unusually acidic immunoglobulin light chains in sera from 4-5 month old MRL/Mp-lpr/lpr mice. Similar light chains were found in lesser amounts in NZB/NZW and BXSB sera, and traces were observed in MRL/Mp-+/+, NZB, and in normal sera. The intensity of the acidic light chain spots increased with age in MRL/Mp-lpr/lpr mice, coincident with the development of autoimmunity. These acidic light chains circulated as components of complete IgG molecules, as they were no longer demonstrable in serum which had been rendered free of IgG by absorption with Cowans strain staphylococci. Because both cryoglobulins and glomerular eluates from MRL/Mp-lpr/lpr mice contained acidic immunoglobulin light chains, these molecules may be involved in immune complex formation and resultant injury.

Class II major histocompatibility antigens and the etiology of systemic lupus erythematosus

It is hypothesized that the underlying immunoregulatory dysfunction in systemic lupus erythematosus (SLE) is altered recognition by T cells of self class II major histocompatibility antigens (Ia). The resultant cellular autoreactivity would directly cause certain of the immunopathological manifestations of SLE. The perception by T cells of self non-MHC antigens in the context of altered Ia on antigen presenting cells would also stimulate specific help for autoantibody production. Autoimmunity induced by the graft-versus-host reaction is an experimental model that illustrates this potential mechanism (A. G. Rolink, S. T. Pals, and E. Gleichmann, J. Exp. Med. 157, 755, 1983; R. A. Eisenberg, S. Y. Craven, and P. L. Cohen, Arth. Rheum. 26, S19, 1983).

Isolation of an interleukin-1-like factor from human joint effusions

Interleukin-1 (IL-1) is a macrophage derived mediator whose properties suggest that it could play a role in the pathology of arthritis. To test this hypothesis, joint fluids from patients with serveral different arthritides were tested. Small amounts of IL-1-like activity were recovered from many of these joint fluids after affinity chromatography over a column of rabbit anti-human IL-1. Positive fluids were obtained from patients with rheumatoid arthritis, psoriatic arthritis, Reiter's syndrome, osteoarthritis, gout, and traumatic arthritis. Upon gel filtration, the joint derived factor displayed a molecular weight distribution similar to that of IL-1 derived from human monocytes stimulated in vitro. These results suggest that IL-1 is present in joint effusions and, therefore, might contribute to joint destruction.

The polypeptide structure of the Sm and RNP nuclear antigens

Sm and nuclear ribonucleoprotein are ubiquitous nuclear antigens towards which important autoantibodies are directed in systemic lupus erythematosus and other human autoimmune syndromes. Using physicochemical techniques and affinity adsorptions, we have purified the polypeptide components of these antigens. The Sm antigen contained polypeptide chains of 15,000 and 17,000 mol. wt. The RNP antigen, which is known by immunochemical techniques to contain the Sm antigen, had the same two polypeptides as well as a larger one of 85,000 mol. wt. This larger peptide was quite labile and apparently broke down into smaller components with manipulation. In addition, the process of affinity purification of the Sm polypeptides gave a product which had increased positive charge. Amino acid analysis of the Sm polypeptides confirmed the presence of relatively large numbers of basic residues. The purified Sm antigen provided an effective reagent for the investigation of autoreactivity to Sm. The differences in structure from our results and those published by others are probably accounted for by the lability of the constituent polypeptides.

Characterization of warm-reactive IgG anti-lymphocyte antibodies in systemic lupus erythematosus. Relative specificity for mitogen-activated T cells and their soluble products

In addition to previously described cold-reactive IgM anti-lymphocyte antibodies maximally cytotoxic for resting cells at 15 degrees C, sera from patients with systemic lupus erythematosus (SLE) were found to contain a new type of antibody preferentially reactive at physiologic temperatures with mitogen-activated lymphocytes. This antibody lacked specificity for unstimulated lymphocytes, and was shown to be of the IgG class both by indirect immunofluorescence and in immunochemical experiments. Certain SLE sera also contained IgG antibodies with the capacity to develop plaques with mitogen-activated T lymphocyte preparations used in a reverse hemolytic plaque assay, indicating reactivity with products released by activated cells. The elimination of the ability of SLE sera to develop plaques after absorption with viable mitogen-stimulated lymphocytes, but not with resting cells, suggested that these antibodies were directed toward activation "neoantigen(s)" shed from the cell surface membrane. Surface membrane phenotype analyses performed by using a variety of monoclonal antibody reagents indicated that the plaque-forming cells (PFC) detected with SLE sera were activated T lymphocytes not restricted to single OKT4+, OKT8+, or Ia antigen+ subpopulations. Essentially all PFC expressed transferrin receptors. The present data raise the possibility that certain of the interesting effects of anti-lymphocyte antibodies on immunologic function in SLE may be mediated by interactions of these new type(s) of antibodies with activated lymphocytes or their products, rather than through blocking or depletion effects on resting precursor cells.

Characterization of warm-reactive IgG anti-lymphocyte antibodies in systemic lupus erythematosus. Relative specificity for mitogen-activated T cells and their soluble products

In addition to previously described cold-reactive IgM anti-lymphocyte antibodies maximally cytotoxic for resting cells at 15 degrees C, sera from patients with systemic lupus erythematosus (SLE) were found to contain a new type of antibody preferentially reactive at physiologic temperatures with mitogen-activated lymphocytes. This antibody lacked specificity for unstimulated lymphocytes, and was shown to be of the IgG class both by indirect immunofluorescence and in immunochemical experiments. Certain SLE sera also contained IgG antibodies with the capacity to develop plaques with mitogen-activated T lymphocyte preparations used in a reverse hemolytic plaque assay, indicating reactivity with products released by activated cells. The elimination of the ability of SLE sera to develop plaques after absorption with viable mitogen-stimulated lymphocytes, but not with resting cells, suggested that these antibodies were directed toward activation "neoantigen(s)" shed from the cell surface membrane. Surface membrane phenotype analyses performed by using a variety of monoclonal antibody reagents indicated that the plaque-forming cells (PFC) detected with SLE sera were activated T lymphocytes not restricted to single OKT4+, OKT8+, or Ia antigen+ subpopulations. Essentially all PFC expressed transferrin receptors. The present data raise the possibility that certain of the interesting effects of anti-lymphocyte antibodies on immunologic function in SLE may be mediated by interactions of these new type(s) of antibodies with activated lymphocytes or their products, rather than through blocking or depletion effects on resting precursor cells.

Activation of T and B lymphocytes in NZB mice

Since NZB mice manifest evidence of intense B cell activation, the state of activation of their T cells was explored. Electron microscopic examination and automated laser light scatter analysis demonstrated the presence of many blast lymphocytes in the spleens of aging NZB mice but not in controls. Only 45% of these large cells were B cells by the criterion of stainable surface IgM. NZB T and B cells were separated using the fluorescence-activated cell sorter; cytographic analysis revealed that both T and B cell populations contained substantial numbers of blast cells. The data thus indicated that T cells, as well as B cells, undergo activation as autoimmunity develops in NZB mice.

Anti-Sm autoantibodies in MRL mice: in vitro detection and generation of antibody-forming cells

Antibodies to the nuclear antigen SM are specific for systemic lupus erythematosus in humans and mice. In order to study the cellular mechanisms of anti-Sm generation, a hemolytic plaque assay to identify and enumerate lymphocytes secreting anti-Sm has been developed by using SRBC coated with purified Sm by a modified carbodiimide technique. Anti-Sm-specific PFC were found in MRL/Mp-Ipr/Ipr and MLR/Mp- +/+ mice whose sera contained anti-Sm, but were never detected in anti-Sm-negative MRL mice or in normals. Spleen cells from anti-Sm-positive MRL/Mp-Ipr/Ipr mice generated anti-Sm PFC spontaneously after 4 days of in vitro culture, whereas cells from normal mice or anti-Sm-negative MRL mice were never observed to produce spontaneous anti-Sm, even when cultured in the presence of bacterial lipopolysaccharide. The generation of anti-Sm by MRL cells in vitro was found to be dependent on the presence of T cells, but the ability of cells from individual MRL mice to generate anti-Sm appeared to be limited by the availability of Sm-specific B cell precursors and not due to a relative absence of T cells capable of providing help for the anti-Sm response. Analysis at the cellular level of the in vitro generation of a disease-specific autoantibody by using the methods described should facilitate understanding of mechanisms of autoreactivity.