bca: an activation-related B-cell gene

We have identified a novel activation related B-cell gene (bca) through differential hybridization screening of a murine B cell cDNA library. The deduced amino acid sequence predicted a protein of 482 amino acids with strong sequence similarity to the SH2 and SH3 domains present within the non-catalytic regions of several protein tyrosine kinases. Northern analysis of RNA from several murine B-cell lines revealed a transcript of 1.8 kb, which was not detected in T-cell and non-lymphoid cell lines. bca was transcribed at low levels in resting spleen cells from a variety of normal mouse strains and was strongly expressed in kidney RNA. bca expression was markedly increased in RNA prepared from mitogen activated B cells, and in freshly isolated spleen and lymph node cells of MRL/lpr and NZB autoimmune strains. The unique sequence of bca, which bears no obvious similarity to any specific class of proteins containing SH2 and SH3 domains, suggests that this gene encodes a novel protein potentially involved in B-cell signal transduction.

Up-regulation of Fas and the costimulatory molecules B7-1 and B7-2 on peripheral lymphocytes in autoimmune B6/gld mice

C57BL/6-gld/gld (B6/gld) mice have a point mutation in the gene for Fas ligand (FasL) resulting in nonfunctional FasL protein. We hypothesized that the lack of normal Fas/FasL interactions in these mice might result in abnormalities of Fas expression. Thus, we compared spleen cells from B6/gld mice and normal B6 control mice. While B6 spleen cells consisted of two main populations, Fashigh (high Fas expression) and Faslow (low Fas expression), nearly all B6/gld spleen cells were Fashigh. Two-color immunofluorescence revealed that the Fashigh and Faslow populations in the B6 spleen were Thy-1.2+ (T cells) and IgM+ (B cells), respectively, whereas both T cells and B cells in the B6/gld spleen were Fashigh, indicating that Fas expression is increased on B cells in the B6/gld spleen. This phenomenon was age related and restricted to peripheral lymphocytes. In addition to Fas, B6/gld splenic B cells showed increased expression of the costimulatory molecule B7-2, while the related costimulatory molecule B7-1 was up-regulated on both B cells and T cells in the B6/gld spleen. In vitro, both B cells and T cells from the B6/gld spleen showed an increase in susceptibility to apoptosis mediated by soluble anti-Fas Ab. These results suggest that some lymphocytes in B6/gld mice are primed to undergo Fas-mediated apoptosis, but are unable to do so due to the absence of functional FasL. Further study of such abnormal lymphocytes in the B6/gld spleen may elucidate the nature of autoimmunity in these mice.

Up-regulation of Fas and the costimulatory molecules B7-1 and B7-2 on peripheral lymphocytes in autoimmune B6/gld mice

C57BL/6-gld/gld (B6/gld) mice have a point mutation in the gene for Fas ligand (FasL) resulting in nonfunctional FasL protein. We hypothesized that the lack of normal Fas/FasL interactions in these mice might result in abnormalities of Fas expression. Thus, we compared spleen cells from B6/gld mice and normal B6 control mice. While B6 spleen cells consisted of two main populations, Fashigh (high Fas expression) and Faslow (low Fas expression), nearly all B6/gld spleen cells were Fashigh. Two-color immunofluorescence revealed that the Fashigh and Faslow populations in the B6 spleen were Thy-1.2+ (T cells) and IgM+ (B cells), respectively, whereas both T cells and B cells in the B6/gld spleen were Fashigh, indicating that Fas expression is increased on B cells in the B6/gld spleen. This phenomenon was age related and restricted to peripheral lymphocytes. In addition to Fas, B6/gld splenic B cells showed increased expression of the costimulatory molecule B7-2, while the related costimulatory molecule B7-1 was up-regulated on both B cells and T cells in the B6/gld spleen. In vitro, both B cells and T cells from the B6/gld spleen showed an increase in susceptibility to apoptosis mediated by soluble anti-Fas Ab. These results suggest that some lymphocytes in B6/gld mice are primed to undergo Fas-mediated apoptosis, but are unable to do so due to the absence of functional FasL. Further study of such abnormal lymphocytes in the B6/gld spleen may elucidate the nature of autoimmunity in these mice.

Endothelial cell expression of intercellular adhesion molecule 1 in experimental posthemorrhagic vasospasm

OBJECTIVE

The exposure of large intracranial arteries to blood after an aneurysmal subarachnoid hemorrhage leads to a cascade of morphological and physiological changes in the vessels, a condition generally described as vasospasm. This response to the periadventitial deposition of blood is mediated in part by the endothelial layer of the vessel. This study was undertaken to examine the role of endothelial cell expression of intercellular adhesion molecule 1 (ICAM-1) in the initiation and regulation of this response.

METHODS

The femoral artery model of vasospasm was used in rats (65 animals, 130 arteries). In each rat, one artery was exposed to blood and the contralateral vessel was exposed to saline, so that each animal served as its own control. Animals were perfused and killed at sequential time points, from 1 hour to 20 days after blood exposure. The vessels were examined immunohistochemically and histologically for the presence of ICAM-1 and morphological features of vasospasm, respectively.

RESULTS

Endothelial cell ICAM-1 immunoreactivity was extensively increased in only the blood-exposed vessels, beginning 3 hours after clot placement and persisting for 24 hours. ICAM-1 immunoreactivity returned to baseline by 48 hours after blood exposure. The influx of inflammatory cells correlated directly with the time and location of increased ICAM-1 expression. Peak arterial remodeling was observed on the blood-exposed side 8 to 12 days after clot placement, as quantified by measurements of increased wall thickness, decreased lumen size, and increased collagen content.

CONCLUSION

Endothelial cell ICAM-1 expression seems to be an early and specific signal used by a vessel in response to the deposition of blood periadventitially. This molecule may be a marker for vessels likely to undergo subsequent morphological remodeling and vasospasm.

B cell genotype determines the fine specificity of autoantibody in lpr mice

Anti-Sm Abs are specific markers of human systemic lupus erythematosus (SLE) and of murine models of this disease. In humans, anti-Sm Abs are mostly IgG1, and in MRL/lpr mice, IgG2a; both are T-dependent isotypes. Other lpr strains, such as B6/lpr, do not produce anti-Sm Ab spontaneously. The present study was aimed at identifying the cellular expression of background genes responsible for generation of the anti-Sm Ab response in MRL/lpr mice. We used double chimeric mice made by transferring MRL/lpr and B6/lpr bone marrows into irradiated allotype heterozygous F1 mice. Five mo after reconstitution, FACS analysis of lymph node (LN) and spleen cells revealed that both MRL/lpr and B6/lpr cells coexisted in roughly equal numbers. Ab produced by each donor could be distinguished by allotype-specific assays. IgG2a anti-Sm was made only by MRL-derived B cells despite the presence of T cells that might potentially provide help to the B6/lpr B cells. The frequency of anti-Sm Ab-producing individuals was similar to that of unmanipulated MRL/lpr mice (about 25%). IgG2a anti-chromatin and total IgG2a was mostly dominated by the MRL-derived B cells. B6-derived B cells produced more rheumatoid factor (RF) against their own IgG2b(b), while RF against IgG2a was dominated by MRL-derived B cells. This suggests that the control of the production of particular autoantibody specificities, such as anti-Sm, is determined by the expression of MRL or B6 background genes in B cells.

B cell genotype determines the fine specificity of autoantibody in lpr mice

Anti-Sm Abs are specific markers of human systemic lupus erythematosus (SLE) and of murine models of this disease. In humans, anti-Sm Abs are mostly IgG1, and in MRL/lpr mice, IgG2a; both are T-dependent isotypes. Other lpr strains, such as B6/lpr, do not produce anti-Sm Ab spontaneously. The present study was aimed at identifying the cellular expression of background genes responsible for generation of the anti-Sm Ab response in MRL/lpr mice. We used double chimeric mice made by transferring MRL/lpr and B6/lpr bone marrows into irradiated allotype heterozygous F1 mice. Five mo after reconstitution, FACS analysis of lymph node (LN) and spleen cells revealed that both MRL/lpr and B6/lpr cells coexisted in roughly equal numbers. Ab produced by each donor could be distinguished by allotype-specific assays. IgG2a anti-Sm was made only by MRL-derived B cells despite the presence of T cells that might potentially provide help to the B6/lpr B cells. The frequency of anti-Sm Ab-producing individuals was similar to that of unmanipulated MRL/lpr mice (about 25%). IgG2a anti-chromatin and total IgG2a was mostly dominated by the MRL-derived B cells. B6-derived B cells produced more rheumatoid factor (RF) against their own IgG2b(b), while RF against IgG2a was dominated by MRL-derived B cells. This suggests that the control of the production of particular autoantibody specificities, such as anti-Sm, is determined by the expression of MRL or B6 background genes in B cells.

Radiation and stress-induced apoptosis: a role for Fas/Fas ligand interactions

The lpr gene encodes a defective form of Fas, a cell surface protein that mediates apoptosis. This defect blocks apoptotic deletion of autoreactive T and B cells, leading to lymphoproliferation and lupus-like autoantibody production. The effects of the lpr Fas mutation on other kinds of physiologically relevant apoptosis are largely undocumented. To assess whether some of the apoptosis known to occur after ionizing radiation might be mediated by Fas/Fas ligand (FasL) interactions, we quantitated in vitro apoptosis by flow cytometry measurement of DNA content in splenic T and B cells from irradiated 5- to 8-month-old B6/lpr mice. Total apoptosis of both lpr and control cells was substantial after treatment; however there was a significant difference between B6 (73%) and lpr (25%) lymphocyte apoptosis. Thy1, CD4, CD8, and IgM cells from lpr showed much lower levels of apoptosis than control cells after irradiation. Apoptosis induced by heat shock was also impaired in lpr. The finding that gamma-irradiation increased Fas expression on B6 cells and that irradiation-induced apoptosis could be blocked with a Fas-Fc fusion protein further supported the possible involvement of Fas in this form of apoptosis. Fas/FasL interactions may thus play an important role in identifying and eliminating damaged cells after gamma-irradiation and other forms of injury.

Fas-dependent CD4+ cytotoxic T-cell-mediated pathogenesis during virus infection

beta 2-Microglobulin-deficient (beta 2m-) mice generate a CD4+ major histocompatibility complex class II-restricted cytotoxic T-lymphocyte (CTL) response following infection with lymphocytic choriomeningitis (LCM) virus (LCMV). We have determined the cytotoxic mechanism used by these CD4+ CTLs and have examined the role of this cytotoxic activity in pathogenesis of LCM disease in beta 2m- mice. Lysis of LCMV-infected target cells by CTLs from beta 2m- mice is inhibited by addition of soluble Fas-Ig fusion proteins or by pretreatment of the CTLs with the protein synthesis inhibitor emetine. In addition, LCMV-infected cell lines that are resistant to anti-Fas-induced apoptosis are refractory to lysis by these virus-specific CD4+ CTLs. These data indicate that LCMV-specific CD4+ CTLs from beta 2m- mice use a Fas-dependent lytic mechanism. Intracranial (i.c.) infection of beta 2m- mice with LCMV results in loss of body weight. Fas-deficient beta 2m- Jpr mice develop a similar wasting disease following i.c. infection. This suggests that Fas-dependent cytotoxicity is not required for LCMV-induced weight loss. A potential mediator of this chronic wasting disease is tumor necrosis factor (TNF)-alpha, which is produced by LCMV-specific CD4+ CTLs. In contrast to LCMV-induced weight loss, lethal LCM disease in beta 2m- mice is dependent on Fas-mediated cytotoxicity. Transfer of immune splenocytes from LCMV-infected beta 2m- mice into irradiated infected beta 2m- mice results in death of recipient animals. In contrast, transfer of these splenocytes into irradiated infected beta 2m- Jpr mice does not cause death. Thus a role for CD4+ T-cell-mediated cytotoxicity in virus-induced immunopathology has now been demonstrated.

Both Sm and DNA are selecting antigens in the anti-Sm B cell response in autoimmune MRL/lpr mice

More than half of the anti-Sm hybridomas isolated from MRL/Mp-lpr/lpr (MRL/lpr) mice produce Abs that also bind ssDNA, and half of these bind dsDNA. Intraclonal comparisons indicate that DNA is a selecting Ag for at least some dual-binding clones. To determine whether Sm itself is a selecting Ag for anti-Sm, we have identified the somatic mutations within the expressed VH and V kappa genes of eight anti-Sm hybridomas, six of which do not bind DNA. We find these V genes have between 0 and 12 somatic mutations each, and that four hybridomas possess a higher number of heavy or light chain CDR replacement (R) mutations than expected by chance, suggesting that these anti-Sm-producing B cells have undergone Ag selection. To demonstrate directly the effect of somatic mutation on Sm binding, we have engineered the unmutated counterpart of Ab 2-12, an Sm-specific hybridoma Ab with a nonrandom distribution of V kappa CDR R mutations, and compared its ability to bind Sm and ssDNA with that of the originally isolated 2-12 Ab. We find that the unmutated Ab has a much lower avidity for Sm than the mutant, but, unlike the mutant, it binds ssDNA. We conclude that Sm can drive clonal expansion in the anti-Sm response, and that Sm-only binding B cells can arise from Sm/DNA dual-binding B cell clonal precursors. These data also suggest that dual binding is not necessary to sustain clonal expansion. Thus, this response is unique in that it can be driven by either of two Ags.

Both Sm and DNA are selecting antigens in the anti-Sm B cell response in autoimmune MRL/lpr mice

More than half of the anti-Sm hybridomas isolated from MRL/Mp-lpr/lpr (MRL/lpr) mice produce Abs that also bind ssDNA, and half of these bind dsDNA. Intraclonal comparisons indicate that DNA is a selecting Ag for at least some dual-binding clones. To determine whether Sm itself is a selecting Ag for anti-Sm, we have identified the somatic mutations within the expressed VH and V kappa genes of eight anti-Sm hybridomas, six of which do not bind DNA. We find these V genes have between 0 and 12 somatic mutations each, and that four hybridomas possess a higher number of heavy or light chain CDR replacement (R) mutations than expected by chance, suggesting that these anti-Sm-producing B cells have undergone Ag selection. To demonstrate directly the effect of somatic mutation on Sm binding, we have engineered the unmutated counterpart of Ab 2-12, an Sm-specific hybridoma Ab with a nonrandom distribution of V kappa CDR R mutations, and compared its ability to bind Sm and ssDNA with that of the originally isolated 2-12 Ab. We find that the unmutated Ab has a much lower avidity for Sm than the mutant, but, unlike the mutant, it binds ssDNA. We conclude that Sm can drive clonal expansion in the anti-Sm response, and that Sm-only binding B cells can arise from Sm/DNA dual-binding B cell clonal precursors. These data also suggest that dual binding is not necessary to sustain clonal expansion. Thus, this response is unique in that it can be driven by either of two Ags.

MHC genes modify systemic autoimmune disease. The role of the I-E locus

The MHC exerts an important influence on systemic autoimmune disease. In C57BL/6-lpr/lpr (B6/lpr) mice, substitution of the H-2d instead of the H-2b MHC haplotype results in a global reduction in autoantibody levels. Since H-2d expresses both I-A and I-E, while H-2b expresses only I-A, general down-regulation of autoimmunity in the d haplotype might be due to I-E expression. This was tested with I-E alpha d transgenic B6/lpr mice, which expressed a functional surface I-E molecule. Five-month-old transgene-positive B6/lpr mice had much lower total IgG, IgG anti-chromatin, anti-DNA, and IgM rheumatoid factor directed against IgG1 and against IgG2b than transgene-negative littermates (p < or = 0.002), as well as significantly lower spleen and lymph node weights (p < or = 0.002). Decreases in autoantibody levels in the transgenic lpr mice were not due to a nonspecific effect of the I-E alpha d transgene, since transgene-positive B6/lpr.H-2d mice had levels of autoantibodies comparable with transgene-negative B6/lpr.H-2d mice. To determine whether autoantibody was preferentially made by I-E-negative B cells, irradiated (B6/lpr.Igha x B6/lpr.I-E alpha d)F1 mice were reconstituted with equal amounts of B6/lpr.Igha and B6/lpr.I-E alpha d bone marrow. Allotype-specific ELISA showed that most autoantibody was produced by the I-E negative B cells (range 97% to 84%). The results show that a functional I-E molecule in lpr mice leads to generalized reduction in autoantibody levels through a direct effect on the B cell. The molecular mechanism of this effect remains to be determined.

MHC genes modify systemic autoimmune disease. The role of the I-E locus

The MHC exerts an important influence on systemic autoimmune disease. In C57BL/6-lpr/lpr (B6/lpr) mice, substitution of the H-2d instead of the H-2b MHC haplotype results in a global reduction in autoantibody levels. Since H-2d expresses both I-A and I-E, while H-2b expresses only I-A, general down-regulation of autoimmunity in the d haplotype might be due to I-E expression. This was tested with I-E alpha d transgenic B6/lpr mice, which expressed a functional surface I-E molecule. Five-month-old transgene-positive B6/lpr mice had much lower total IgG, IgG anti-chromatin, anti-DNA, and IgM rheumatoid factor directed against IgG1 and against IgG2b than transgene-negative littermates (p &lt; or = 0.002), as well as significantly lower spleen and lymph node weights (p &lt; or = 0.002). Decreases in autoantibody levels in the transgenic lpr mice were not due to a nonspecific effect of the I-E alpha d transgene, since transgene-positive B6/lpr.H-2d mice had levels of autoantibodies comparable with transgene-negative B6/lpr.H-2d mice. To determine whether autoantibody was preferentially made by I-E-negative B cells, irradiated (B6/lpr.Igha x B6/lpr.I-E alpha d)F1 mice were reconstituted with equal amounts of B6/lpr.Igha and B6/lpr.I-E alpha d bone marrow. Allotype-specific ELISA showed that most autoantibody was produced by the I-E negative B cells (range 97% to 84%). The results show that a functional I-E molecule in lpr mice leads to generalized reduction in autoantibody levels through a direct effect on the B cell. The molecular mechanism of this effect remains to be determined.

Phenotypic abnormalities of splenic and bone marrow B cells in lpr and gld mice

Mice homozygous for the mutant Fas gene lpr develop generalized lymphoproliferation and produce autoantibodies resembling those found in human SLE. We have previously shown that these autoantibodies are produced by B2 cells rather than B1 cells and that the autoantibody- producing B cells are intrinsically abnormal. We investigated further the lpr B cell with a large panel of antibodies to B-cell surface markers to identify phenotypic abnormalities. B cells from spleen and bone marrow of age-matched congenic mice differing only at the lpr locus were examined by flow cytometry. Two consistent phenotypic differences were identified. First, spleen cells from older lpr mice had an increase in the number and percentage of IgM+ B cells expressing low levels of CD23. Second, lpr bone marrow had decreased numbers of B220hiIgM+-syndecan-1+CD23+ B cells. All other markers tested, except the previously identified modest increase of Ia on lpr spleen cells, showed no consistent differences. B cells from gld mice showed the same phenotypic abnormalities as those from lpr. Compared to T cells, the relative paucity of cell surface marker differences between lpr and +/+ B cells suggests that B cells may have fewer regulatory mechanisms to silence autoreactive specificities. The phenotypic differences identified may provide clues to the mechanism of autoantibody production in lpr mice, while the overwhelming phenotypic similarity between lpr and +/+ B cells suggests that the major abnormality of lpr B cells may lie in their specificity, that is, in their inability to delete autoreactive subsets.

Suppression and reversal of gld disease by parabiosis with normal mice

The disruption of the Fas receptor or Fas ligand by the lpr or gld mutations, respectively, results in severe autoimmune and lymphoproliferative disease due to the failure of Fas-mediated deletion of self-reactive lymphocytes. Recently, we have shown in mixed chimeras that gld-induced autoimmunity could be corrected by normal bone marrow, in particular by normal T cells. In contrast, lpr-mediated autoimmunity could not be influenced by normal bone marrow-derived cells. In the present report, we have studied the role of normal lymphocytes in suppressing or reversing gld-induced autoimmunity by parabiosis with normal mice. Our results show a suppression of lymphadenopathy, fewer CD4-CD8- T cells, and lower levels of autoantibody production in gld mice parabiosed with normal mice at 4-6 weeks of age. The gld mice parabiosed with normal mice at 4 months of age also exhibited a substantial reduction of both total and CD4-CD8- T cells in the periphery 2 months after surgery. However, they showed little reduction of autoantibodies compared to gld mice parabiosed with gld mice. In contrast, older lpr mice did not exhibit any reduction in lymphadenopathy or autoantibody production after parabiosis with normal mice. The prevention or reversal of lymphadenopathy in parabiosed gld mice suggests that ongoing Fas-mediated deletion in the periphery may play an important role in maintaining self-tolerance. The relative irreversibility of autoantibody synthesis in older parabiosed gld mice suggests that autoantibody-producing B cells or their committed precursors are long lived and do not express functional Fas receptor.

The Yaa gene-mediated acceleration of murine lupus: Yaa- T cells from non-autoimmune mice collaborate with Yaa+ B cells to produce lupus autoantibodies in vivo

The BXSB Y chromosome-linked mutant gene, Yaa, promotes autoimmune responses in mice predisposed to a lupus-like autoimmune disease. We have previously shown that a cognate interaction of T cells with B cells expressing the Yaa gene appears to be responsible for the accelerated production of autoantibodies. To investigate whether T cells that provide help for autoantibody production by Yaa+ B cells need to express the Yaa gene, we have made radiation bone marrow chimeras containing two sets of T and B cells from mice with or without the Yaa gene and differing by the Thy-1 and Igh allotypes. We then determined autoantibody production following the selective elimination of T cells of Yaa+ origin by treating mice with allele-specific anti-Thy-1 monoclonal antibody. Our results demonstrated that the selective production of autoantibodies by Yaa+ B cells in Yaa(+)-Yaa- double bone marrow chimeras can be mediated as efficiently by T cells from non-autoimmune mice lacking the Yaa gene as by T cells from autoimmune mice bearing the Yaa gene. This indicates that T cells from non-autoimmune Yaa- mice are capable of providing help for autoimmune responses by collaborating with Yaa+ B cells. These data thus strongly suggest that the Yaa gene defect is not functionally expressed in T cells, but only in B cells, and contrast with parallel experiments in the lpr model, in which defects of the Fas antigen in both T and B cells are crucial for the lpr gene-mediated promotion of autoantibody production.

bcl-2 transgenic Lpr mice show profound enhancement of lymphadenopathy

The lpr gene encodes a defective form of the fas gene that mediates apoptosis, and its expression results in autoantibodies and massive lymphadenopathy. bcl-2, another gene locus that affects programmed cell death, acts to inhibit apoptosis. Since multiple mechanisms controlling programmed cell death may contribute to systemic autoimmunity, the effect of the bcl-2 transgene on the lpr model was examined by crossing bcl-2 transgenic and C57BL/6-lpr mice. Compared with bcl-2-/lpr mice, bcl-2+/lpr showed dramatic increases in lymphadenopathy and T cell accumulation, but not in autoantibodies or B cell numbers. Short term transfer studies demonstrated that double negative T cells normally have a limited lifespan, and their survival is enhanced by the bcl-2 transgene. Thus, defects in separate apoptosis mechanisms may combine to produce enhanced pathologic effects.

bcl-2 transgenic Lpr mice show profound enhancement of lymphadenopathy

The lpr gene encodes a defective form of the fas gene that mediates apoptosis, and its expression results in autoantibodies and massive lymphadenopathy. bcl-2, another gene locus that affects programmed cell death, acts to inhibit apoptosis. Since multiple mechanisms controlling programmed cell death may contribute to systemic autoimmunity, the effect of the bcl-2 transgene on the lpr model was examined by crossing bcl-2 transgenic and C57BL/6-lpr mice. Compared with bcl-2-/lpr mice, bcl-2+/lpr showed dramatic increases in lymphadenopathy and T cell accumulation, but not in autoantibodies or B cell numbers. Short term transfer studies demonstrated that double negative T cells normally have a limited lifespan, and their survival is enhanced by the bcl-2 transgene. Thus, defects in separate apoptosis mechanisms may combine to produce enhanced pathologic effects.

Sm and DNA binding by dual reactive B cells requires distinct VH, V kappa, and VH CDR3 structures

We have previously demonstrated an overlap of the anti-Sm and anti-DNA responses in MRL/Mp-lpr/lpr mice. The Ab produced by many anti-Sm hybridomas bind DNA and are encoded by Ig V genes used by anti-DNA hybridomas. In addition, some anti-Sm Ab that bind DNA have acquired mutations that improve DNA binding, indicating that DNA is a selecting Ag in the anti-Sm response. To gain insight into the basis for the dual binding ability of these Ab, we coexpressed the H chain from the anti-Sm hybridoma 2-12 with nine different L chains. Hybridoma 2-12 binds Sm but not DNA, yet expresses the same J558 VH gene as three anti-Sm hybridomas that bind ssDNA and at least one anti-DNA hybridoma that does not bind Sm. We found that most of the transfectoma Ab bind Sm, but their avidities vary over more than 3 orders of magnitude. Five of the nine transfectoma Ab bind ssDNA, and none bind dsDNA. In general, the ability to bind each Ag follows the binding ability of the hybridoma from which the L chain is derived. H Chain swapping experiments indicate that the H chain, VH CDR3 in particular, contributes to the binding of both Sm and DNA. We conclude that Sm and DNA select for distinct features of VH, V kappa, and VH CDR3, suggesting selection by both Ag in the anti-Sm response.

Sm and DNA binding by dual reactive B cells requires distinct VH, V kappa, and VH CDR3 structures

We have previously demonstrated an overlap of the anti-Sm and anti-DNA responses in MRL/Mp-lpr/lpr mice. The Ab produced by many anti-Sm hybridomas bind DNA and are encoded by Ig V genes used by anti-DNA hybridomas. In addition, some anti-Sm Ab that bind DNA have acquired mutations that improve DNA binding, indicating that DNA is a selecting Ag in the anti-Sm response. To gain insight into the basis for the dual binding ability of these Ab, we coexpressed the H chain from the anti-Sm hybridoma 2-12 with nine different L chains. Hybridoma 2-12 binds Sm but not DNA, yet expresses the same J558 VH gene as three anti-Sm hybridomas that bind ssDNA and at least one anti-DNA hybridoma that does not bind Sm. We found that most of the transfectoma Ab bind Sm, but their avidities vary over more than 3 orders of magnitude. Five of the nine transfectoma Ab bind ssDNA, and none bind dsDNA. In general, the ability to bind each Ag follows the binding ability of the hybridoma from which the L chain is derived. H Chain swapping experiments indicate that the H chain, VH CDR3 in particular, contributes to the binding of both Sm and DNA. We conclude that Sm and DNA select for distinct features of VH, V kappa, and VH CDR3, suggesting selection by both Ag in the anti-Sm response.

Expression of Hodgkin's disease associated antigen BLA.36 in anaplastic large cell lymphomas and lymphomatoid papulosis primarily of T-cell origin

Monoclonal antibody BLA.36 stains Reed-Sternberg (RS) cells and their mononuclear variants, as well as some benign and malignant cells of B-cell lineage, and retains its immunoreactivity in formalin- and B5-fixed tissue. The origin of the RS cell is controversial and the distinction between Hodgkin's disease (HD), anaplastic large cell lymphoma (ALCL), and lymphomatoid papulosis (LyP) (the latter two primarily T-cell in origin), can be difficult. The authors studied expression of BLA.36 in 22 cases of ALCL, 13 cases of LyP, and 15 cases of HD. Most atypical or malignant cells stained for BLA.36 in 10 of 22 cases of ALCL, 9 of 13 cases of LyP, and 9 of 15 cases of HD. Additional immunohistochemistry or gene rearrangement analysis indicated a T-cell origin for 8 of 10 BLA.36 positive ALCL, and 9 of 9 BLA.36 positive LyP cases. BLA.36 was expressed by T-cell lines derived from two ALCLs and one CD30+ cell line derived from LyP. The authors conclude that BLA.36 is not specific for lymphomas of B-cell origin and cannot be used to distinguish between HD, ALCL, and LyP with RS-like cells. These results further support a relationship between HD, ALCL, and LyP and suggest that RS cells are histogenetically related to both B- and T-lymphocytes.

Absence of autoantigen Ku in mature human neutrophils and human promyelocytic leukemia line (HL-60) cells and lymphocytes undergoing apoptosis

The Ku autoantigen is a heterodimer of 70- and 80-kD proteins recognized by autoantibodies from patients with systemic lupus erythematosus and related diseases that is the DNA-binding component of a DNA-dependent protein kinase. The catalytic activity of DNA-dependent protein kinase is carried by a 350-kD subunit (p350). In light of the recently described role of Ku in repairing double-strand DNA breaks, we investigated the regulation of Ku and p350 levels in neutrophils, a terminally differentiated cell type destined to undergo apoptosis. Since the appearance of double-strand DNA breaks is characteristic of apoptosis, we were interested in the possibility that Ku might oppose programmed cell death. Analysis of peripheral blood cells by flow cytometry using anti-Ku and anti-p350 monoclonal antibodies revealed that neutrophils were unstained, whereas resting (G0) lymphocytes were positive. The absence of Ku in mature neutrophils was confirmed by Western blotting and enzyme-linked immunosorbent assay for Ku antigen. In contrast, the human promyelocytic leukemia line, HL-60, which undergoes differentiation toward neutrophils after dimethylsulfoxide treatment, was positive for Ku and p350. In view of the short lifespan of neutrophils and the prolonged half-life of Ku and p350 (> 5 d), these data suggested that Ku was actively degraded during myeloid differentiation. Analysis of HL-60 cells by flow cytometry revealed that Ku staining was bimodal. Cells in G1/G0, S, or G2/M were all stained positively, whereas cells with a subdiploid DNA content characteristic of apoptosis were Ku negative. Similar results were obtained with phytohemagglutin-stimulated human lymphocytes. These data suggest that the Ku antigen is actively degraded in both myeloid cells destined to undergo apoptosis and apoptotic lymphocytes, raising the possibility that degradation of Ku may help to prevent the inappropriate repair of fragmented nuclear DNA during apoptosis.