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.

Subclass restriction of anti-Sm antibodies in MRL mice

The subclass distribution of anti-Sm antibodies in the serum of MRL/Mp-Ipr/Ipr and MRL/Mp- +/+ mice was investigated with a sensitive ELISA technique. In both strains, but particularly in the Ipr mice, anti-Sm antibodies were predominantly of the IgG2a isotype. This preponderance was not an artifact of the sensitivity or specificity of the subclass-specific anti-Sm ELISA, nor did it reflect the subclass distribution of total serum IgG. A plaque-forming cell assay for anti-Sm antibodies also showed a predominance of the IgG2a isotype, indicating that the serum findings could not be explained by differential catabolism of IgG subclasses. Finally, antibodies to double-stranded DNA, as detected by the Crithidia luciliae assay, did not show a restricted subclass distribution. The isotype expression of anti-Sm antibodies in MRL mice must reflect in vivo mechanisms regulating the production of these autoantibodies. The IgG2a restriction in particular suggests an important in vivo role for T cells.

T cell recognition of the Sm nuclear antigen: induction of T cell proliferative responses in MRL/Mp- +/+ mice

The role of T cell immunity against nuclear antigens recognized by autoantibodies in human and murine systemic lupus is unclear. We have studied the T cell proliferative response to purified Sm nuclear antigen by measuring in vitro 3H-thymidine incorporation by MRL/Mp- +/+ lymph node cells primed with Sm in Freund's adjuvant. Sm-primed cells responded in a dose-dependent fashion when cultured in vitro with purified Sm. Absorption of the Sm with solid-phase anti-Sm IgG from either of two lupus patients ablated the response, whereas control absorptions with normal IgG had no effect. Furthermore, cells from mice primed with physicochemically purified Sm responded in vitro to affinity-purified antigen, and vice versa. Treatment of cells with either anti-Thy-1 or anti-Lyt-1 and C eliminated Sm-induced proliferation, whereas anti-Lyt-2 treatment resulted in enhanced responses. MRL/Mp- +/+ mice, which made no detectable anti-Sm antibodies in vivo, were nonetheless capable of generating Sm-reactive T cells. These results indicate that T cells can specifically recognize the Sm nuclear antigen. Such recognition may be of importance in the generation of antibodies to Sm and other nuclear antigens in vivo.

T cell recognition of the Sm nuclear antigen: induction of T cell proliferative responses in MRL/Mp- +/+ mice

The role of T cell immunity against nuclear antigens recognized by autoantibodies in human and murine systemic lupus is unclear. We have studied the T cell proliferative response to purified Sm nuclear antigen by measuring in vitro 3H-thymidine incorporation by MRL/Mp- +/+ lymph node cells primed with Sm in Freund's adjuvant. Sm-primed cells responded in a dose-dependent fashion when cultured in vitro with purified Sm. Absorption of the Sm with solid-phase anti-Sm IgG from either of two lupus patients ablated the response, whereas control absorptions with normal IgG had no effect. Furthermore, cells from mice primed with physicochemically purified Sm responded in vitro to affinity-purified antigen, and vice versa. Treatment of cells with either anti-Thy-1 or anti-Lyt-1 and C eliminated Sm-induced proliferation, whereas anti-Lyt-2 treatment resulted in enhanced responses. MRL/Mp- +/+ mice, which made no detectable anti-Sm antibodies in vivo, were nonetheless capable of generating Sm-reactive T cells. These results indicate that T cells can specifically recognize the Sm nuclear antigen. Such recognition may be of importance in the generation of antibodies to Sm and other nuclear antigens in vivo.

Subclass restriction of anti-Sm antibodies in MRL mice

The subclass distribution of anti-Sm antibodies in the serum of MRL/Mp-Ipr/Ipr and MRL/Mp- +/+ mice was investigated with a sensitive ELISA technique. In both strains, but particularly in the Ipr mice, anti-Sm antibodies were predominantly of the IgG2a isotype. This preponderance was not an artifact of the sensitivity or specificity of the subclass-specific anti-Sm ELISA, nor did it reflect the subclass distribution of total serum IgG. A plaque-forming cell assay for anti-Sm antibodies also showed a predominance of the IgG2a isotype, indicating that the serum findings could not be explained by differential catabolism of IgG subclasses. Finally, antibodies to double-stranded DNA, as detected by the Crithidia luciliae assay, did not show a restricted subclass distribution. The isotype expression of anti-Sm antibodies in MRL mice must reflect in vivo mechanisms regulating the production of these autoantibodies. The IgG2a restriction in particular suggests an important in vivo role for T cells.

Anti-idiotypic antibodies to the Coombs antibody in NZB F1 mice

The F1 hybrids of NZB and several normal mouse strains are known to produce less anti-erythrocyte (Coombs) autoantibody and develop a milder hemolytic anemia than their NZB parents. We have found that serum from some (NZB x CBA)F1 mice agglutinated erythrocytes from certain Coombs-positive NZB mice, often in extremely high titer, whereas other (CBA x NZB)F1 sera agglutinated erythrocytes from different individual NZB mice. The agglutination was due to antibody, but was not due to rheumatoid factor activity. Because F(ab')2 fragments of the F1 sera agglutinated erythrocytes coated with F(ab')2 fragments of the appropriate NZB sera, the observed reactivity was probably caused by idiotype-anti-idiotype interactions. In addition, because F1 sera could not agglutinate mouse erythrocytes coated with monovalent NZB Fab' fragments, the recognized idiotype probably involved the antigen-binding site. Anti-idiotypic antibodies against anti-erythrocyte autoantibodies may play an important role in the regulation of autoantibody formation.

Association between endogenously activated T cells and immunoglobulin-secreting B cells in patients with active systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by increased numbers of circulating B cells activated polyclonally to secrete immunoglobulin. Because T cells secrete, or shed, various factors that are functionally important in regulating immunoglobulin production by B cells, a reverse hemolytic plaque assay was developed to quantitate such activated T cells. In this technique, we used a rabbit antiserum raised to supernatants of concanavalin-A--stimulated human lymphocytes. The relevant antigenic specificity of this antiserum is directed toward the shed surface membrane determinant(s) preferentially expressed on activated T cells. Freshly isolated peripheral blood mononuclear cells from 14 SLE patients contained more than 10 times the number of endogenously activated T cells than cells from normal subjects. Within the SLE group, plaque-forming T cells were particularly increased in patients with active disease. By linear regression analysis, a significant positive correlation was revealed between such activated T cells and immunoglobulin-secreting B cells, also measured by a reverse plaque assay (r = 0.83). It appears that both activated B cells and T cells circulate in increased numbers in SLE. Additional investigation will be required to define the molecular nature of the T cell product(s) being measured and to clarify the relationship of these findings to the immunoregulatory abnormalities in this disorder.

Activated T cells in human peripheral blood: quantitation with a reverse hemolytic plaque assay

Rabbit antiserum to culture supernatant of concanavalin A-stimulated peripheral blood mononuclear cells was used in a reverse hemolytic plaque assay to detect activated T lymphocytes in human peripheral blood. The number of plaque-forming cells in fresh, unstimulated lymphocyte preparations was approximately 400/10(6) cells, and increased 7- to 14-fold after stimulation with a variety of mitogens and antigens. The kinetics of the increase paralleled 3H-thymidine incorporation, with a maximum on day 3 of culture. Plaques were eliminated by treatment of cells with anti-Leu-I + complement or by depletion of E-rosettes. The activated T cells were not restricted to a given inducer, suppressor, or Ia+ T cell subset, however. Both mitogen-stimulated culture supernatants and mitogen-activated lymphocytes, but not resting lymphocytes, were effective in absorbing the capacity of the rabbit antiserum to develop plaques. This suggested that the predominant specificity of this antiserum was directed toward surface membrane determinant(s) of T cells actively shed into the medium. This process was shown to require ongoing protein synthesis, and, in mitogen-stimulated lymphocyte preparations, DNA synthesis as well. This approach has enabled detection of a surprisingly large number of endogenously activated T cells in normal human blood, and should be useful for the analysis of immunoregulatory events at the single-cell level.

Activated T cells in human peripheral blood: quantitation with a reverse hemolytic plaque assay

Rabbit antiserum to culture supernatant of concanavalin A-stimulated peripheral blood mononuclear cells was used in a reverse hemolytic plaque assay to detect activated T lymphocytes in human peripheral blood. The number of plaque-forming cells in fresh, unstimulated lymphocyte preparations was approximately 400/10(6) cells, and increased 7- to 14-fold after stimulation with a variety of mitogens and antigens. The kinetics of the increase paralleled 3H-thymidine incorporation, with a maximum on day 3 of culture. Plaques were eliminated by treatment of cells with anti-Leu-I + complement or by depletion of E-rosettes. The activated T cells were not restricted to a given inducer, suppressor, or Ia+ T cell subset, however. Both mitogen-stimulated culture supernatants and mitogen-activated lymphocytes, but not resting lymphocytes, were effective in absorbing the capacity of the rabbit antiserum to develop plaques. This suggested that the predominant specificity of this antiserum was directed toward surface membrane determinant(s) of T cells actively shed into the medium. This process was shown to require ongoing protein synthesis, and, in mitogen-stimulated lymphocyte preparations, DNA synthesis as well. This approach has enabled detection of a surprisingly large number of endogenously activated T cells in normal human blood, and should be useful for the analysis of immunoregulatory events at the single-cell level.

Bone marrow as the major site of antierythrocyte autoantibody production in NZB mice

By use of a hemolytic plaque assay, it has been determined that most cells secreting the clinically important (anti-X) erythrocyte autoantibody of NZB mice are located in the bone marrow. There was evidence of excessive polyclonal B cell activation in NZB spleen but not in bone marrow, despite the role of marrow as the major source of erythrocyte autoantibody. These findings suggest that polyclonal activation of B cells within the marrow does not lead to erythrocyte autoantibody production. Small but significant numbers of antierythrocyte autoantibody producing cells were detected in the bone marrow but not in the spleens of normal mice, indicating that tolerance to erythrocytes may be less absolute in the bone marrow than in the spleen, or that the bone marrow serves as a repository for autoantibody secreting cells generated elsewhere.

Defective B cell tolerance in adult (NZB X MZW)F1 mice

Hapten-specific tolerance was induced in vitro by trinitrophenyl-human gamma globulin (TNP32HGG) to a comparable degree in B cells from adult autoimmune (NZB X NZW)F1 (B/W) mice and normal BDF1, CBA/J, and DBA/1J mice. When a lower epitope density tolerogen (TNP7HGG) was used, B/W mice were significantly less sensitive than normal mice to the induction of B cell tolerance. This finding of defective B cell tolerance in adult B/W mice is consistent with previous reports that document other B cell abnormalities that may relate to the expression of autoimmune disease.

Functional absence of a B cell subpopulation in ageing New Zealand mice

As has been found for spleen cells from ageing NZB x NZW (B/W) mice, ageing NZB mice were also found to make no antibody when stimulated in vitro with the polyclonal B cell activators (PBA) LPS and PPD. This immune defect was not due to the action of suppressor cells, since old NZB and B/W spleen cells did not suppress the PBA response of young spleen cells. Spleen cells from aged NZB mice were not able to generate antibody-forming cells when stimulated with the thymus-independent antigen, TNP-LPS, but were able to produce antibody in response to another thymus-independent antigen, TNP-AECM-Ficoll, thereby implying that there is a selective functional deletion of a B cell subpopulation in ageing New Zealand mice. The failure of B/W and NZB spleen cells to generate antibody in response to PBA is interpreted as a consequence of a continuing in vivo polyclonal B cell activation accompanying the development of autoimmune disease, leading to a scarcity of B cells available for activation by PBA and by some thymus-independent antigens in vitro.

Abnormal polyclonal B cell activation in NZB/NZW F1 mice

Spleen cells from autoimmune (10-mont-old) NZB/NZW (B/W) mice failed to generate appreciable numbers of antibody-forming cells (AFC) in vitro to TNP-substituted sheep erythrocytes in response to the polyclonal B cell activators (PBA), LPS and PPD, despite normal DNA synthetic responses to these agents and normal AFC responses to TNP-Ficoll. The failure to respond to PBA in old B/W mice was not due to suppressor T cells since anti-brain-associated-theta-treated spleen cells still failed to generate AFC in response to PBA. The defect was age-related since cells from young B/W mice generated vigorous AFC responses to PBA. It is suggested that the failure of the spleen cells of old B/W mice to generate AFC is a result of in vitro polyclonal B cell activation in the course of autoantibody formation.

Induction of guinea pig antibody responses in vitro

Guinea pig spleen cells cultured together with peritoneal exudate lymphocytes (PEL) were found to generate large numbers of antibody-forming cells (AFC) in vitro in response to hapten-protein antigens. Neither cell type cultured alone yielded appreciable responses. Strain 13 or F1 (Strain 2 X Strain 13) lymphocytes, but not those from strain 2 animals, are able to respond to the genetically controlled antigen, DNP-guinea pig albumin (DNP-GPA). Antisera directed against responder (strain 13) parent Ia antigens selectively blocked the generation of AFC by F1 (strain 2 X strain 13) spleen-PEL mixtures in response to DNP-GPA. Both allogeneic (strain 2) and syngeneic macrophages functioned equally well in presentation of DNP-GPA to strain 13 lymphocytes.

In vitro studies of the genetically determined unresponsiveness to thymus-independent antigens in CBA/N mice

The X-chromosome-linked B lymphocyte defect of CBA/N mice has been studied in vitro by comparing the ability of (CBA/N X DBA/2)F1 (X-/X- X X+/Y) male (X-/Y) and female (X-/X+) spleen cells to respond to the thymus-independent antigen DNP (or TNP)-AECM-Ficoll. (CBA/N X DBA/2)F1 male spleen cells failed to generate significant in vitro anti-TNP antibody responses to DNP- or TNP-AECM-Ficoll, in contrast to spleen cells from F1 female (X-/X+) mice which responded normally to these T-independent antigens. Spleen cells from male F1 mice responded almost as well as F1 female cells to the thymus-dependent antigen, TNP-sheep red blood cells (TNP-SRBC) in vitro. Adding F1 male cells to F1 female cells failed to reduce the response of the latter to DNP-AECM-Ficoll, suggesting that the inability of F1 male cells to respond was not due to active suppression. The response of F1 male spleen cells to TNP-SRBC was not impaired by adding high concentrations of TNP-AECM-Ficoll indicating that the mechanism of unresponsiveness was not tolerance induction in all TNP-specific precursors. Lymphocytes from F1 male mice were capable of forming anti-TNP antibody after stimulation with lipopolysaccharide (LPS) in high concentrations; DNP-AECM-Ficoll had no effect on this polyclonal response. B lymphocytes from mice bearing only the X-chromosome of the CBA/N strain thus display a profound defect in B cell activation. This functional defect may represent either an inability of the defective B cells to be activated by thymus-independent antigens or the absence of a sub-class of B cells which respond to thymus-independent antigens.

Immunologic effects of neonatal infection with mouse thymic virus

Mouse thymic virus is a herpesvirus that causes extensive thymic necrosis when given to newborn mice. During the time of acute infection spleen cells have markedly diminished reactivity to T cell phytomitogens and to allogeneic cells and are incapable of effecting a primary in vitro response to a "T-dependent" antigen; responses to B cell mitogens and to a T-independent antigen are unimpaired. Spleens from acutely infected mice have low theta antigen normal numbers of immunoglobulin-bearing cells. Surprisingly, despite widespread necrosis and cellular depletion, thymic cell reactivity to mitogens is unimpaired. However, the ability to thymocytes to proliferate and to generate cytotoxic killer cells in response to allogeneic cells is diminished.

Ontogeny of mouse T-lymphocyte function

The development of lymphocytes within the fetal and neonatal BALB/c mouse thymus is reviewed with particular emphasis on the maturity of immunologic functions. Fetal thymocytes respond by vigorous proliferation to stimulation by allogeneic lymphoid cells or by phytohemagglutinin. Such reactivity is much diminished in neonatal thymus or thymic-derived (T) cells in neonatal spleen. Splenic T cells seem to mature more slowly than immunoglobulin-bearing B lymphocytes in the neonatal spleen, but the finding is confounded by the presence of large numbers of "suppressor" T cells in the neonatal spleen. For example, the in vitro antibody response to the T-independent antigen dinitrophenyl-lysine-Ficoll is optimal by 2 or 3 weeks of age, but the in vitro response to T-dependent sheep erythrocytes does not reach adult levels until 6 weeks of age, suggesting a deficiency in T "helper cells." The response of neonatal spleen cells to sheep erythrocytes cannot be reconstituted by adult T cells however, unless neonatal splenic T cells are first depleted by anti-Thy 1 serum and complement. The target of this T suppressor cell seems to be only B cells, and not other T cells. The overall sequence of T lymphocyte maturation in the mouse seems to start with large numbers of reactive T cells as well as some functionally active helper or effector T cells in early neonatal life, and finally to achieve a stable equilibrium between T cell subpopulations between 5 and 6 weeks of age.