B-cell function in mice treated with anti-IgD from birth

Peripheral B cell tolerance and function in transgenic mice expressing an IgD superantigen

Transitional B cells turn over rapidly in vivo and are sensitive to apoptosis upon BCR ligation in vitro. However, little direct evidence addresses their tolerance sensitivity in vivo. A key marker used to distinguish these cells is IgD, which, through alternative RNA splicing of H chain transcripts, begins to be coexpressed with IgM at this stage. IgD is also expressed at high levels on naive follicular (B-2) and at lower levels on marginal zone and B-1 B cells. In this study, mice were generated to ubiquitously express a membrane-bound IgD-superantigen. These mice supported virtually no B-2 development, a greatly reduced marginal zone B cell population, but a relatively normal B-1 compartment. B cell development in the spleen abruptly halted at the transitional B cell population 1 to 2 stage, a block that could not be rescued by either Bcl-2 or BAFF overexpression. The developmentally arrested B cells appeared less mature and turned over more rapidly than nontransgenic T2 cells, exhibiting neither conventional features of anergy nor appreciable receptor editing. Paradoxically, type-2 T-independent responses were more robust in the transgenic mice, although T-dependent responses were reduced and had skewed IgL and IgH isotype usages. Nevertheless, an augmented memory response to secondary challenge was evident. The transgenic mice also had increased serum IgM, but diminished IgG, levels mirrored by the increased numbers of IgM(+) plasma cells. This model should facilitate studies of peripheral B cell tolerance, with the advantages of allowing analysis of polyclonal populations, and of B cells naturally lacking IgD.

Altered expression of the Salmonella typhimurium-specific B-cell repertoire in mice chronically treated with antibodies to immunoglobulin D

Using a modification of the splenic focus assay, we analyzed the Salmonella typhimurium-specific B-cell repertoire in salmonella-susceptible BALB/c mice. Although these mice normally succumbed to salmonella infection before antibody was produced, they appeared to have splenic S. typhimurium-specific B-cell precursors that could be activated to differentiate and secrete antibody in a manner which was quantitatively and qualitatively identical to that of salmonella-resistant mouse strains. We also analyzed the primary S. typhimurium-specific B-cell repertoire in BALB/c mice that had been chronically treated with antibodies to immunoglobulin D (IgD) and therefore had no surface IgD-positive B cells. Although the frequency of S. typhimurium-specific precursors in these mice was similar to that of control mice, there was an apparent alteration in the isotype distribution pattern in anti-IgD-treated mice. Control mice generated a significantly greater proportion of IgG-secreting clones than did anti-IgD-treated mice. In addition, a greater proportion of S. typhimurium-specific clones from control mice secreted IgG2 than secreted IgG1, and those clones that secreted IgG2 but not IgM, IgG3, or IgG1 were greater than 20-fold more common in control than in anti-IgD-treated mice. Finally, we analyzed the immune response of control and anti-IgD-treated mice to a live avirulent vaccine, S. typhimurium SL3235. Although both groups were protected after challenge with a live virulent S. typhimurium strain, only the control mice made serum antibodies to this vaccine. Taken together, these results show that (i) salmonella-susceptible BALB/c mice have S. typhimurium-specific B cells, (ii) the S. typhimurium-specific B cells in anti-IgD-treated mice may have a restricted capacity to switch heavy-chain classes, (iii) the similarity observed in the frequency of the S. typhimurium-specific precursors for these two groups of BALB/c mice is not reflected in the serum, and (iv) the failure of anti-IgD-treated mice to generate a serum antibody response to SL3235 in the face of complete protection suggests that this model may be used to study cell-mediated immune mechanisms in the apparent absence of humoral immunity.

Induction and properties of syngeneic murine anti-immunoglobulin D

High titers of autoantibodies directed to isotypic determinants of IgD were produced by inoculation of syngeneic monoclonal IgD, conjugated covalently to keyhole limpet hemocyanin, into adult or neonatal inbred mice. Anti-idiotypic antibodies were induced at the same time. The average affinity of the mouse antibodies (Ka approximately equal to 10(7) M-1) is similar to that of rabbit anti-IgD and of syngeneic anti-IgE induced by the same procedure. Results indicate that B cells of the mice are not tolerant to serum IgD and that tolerance is maintained at the level of T cells. Direct interaction of the syngeneic anti-IgD with cell-surface IgD was minimal, and there was no convincing evidence that cell-surface IgD was down-regulated in the anti-IgD-producing mice. Further studies, preferably employing monoclonal anti-IgD, are required to determine whether epitopes on cell-surface IgD can be recognized by syngeneic anti-IgD. The ability to generate in vivo high titers of anti-IgD should facilitate the production of such monoclonal antibodies.

Physiology of IgD. III. Effect of treatment with anti-IgD from birth on the magnitude and isotype distribution of the immune response in the spleen

Continued treatment with monoclonal anti-IgD (Ig-5a) from birth in BALB/c mice causes a markedly increased responsiveness to i.v. injected dinitrophenylated ovalbumin (DNP-OVA) with Bordetella pertussis at the age of 8 weeks. The 19S plaque-forming cell (PFC)/spleen response is particularly enhanced, 6-8-fold, but all the other isotypes also show increases of 2-6-fold, including IgA and IgE. Both primary and secondary PFC responses and serum antibody titers are enhanced. After transfer of spleen cells from anti-Ig-treated mice to irradiated recipients the IgM/IgG ratio becomes similar to that of controls. In contrast, the response of anti-IgD-treated mice to i.p. immunization with either 0.2 or 100 micrograms DNP-OVA plus alum is reduced by approximately 80% for each Ig isotype except IgM and remains low upon transfer of spleen cells to recipients. It is concluded that the paucity of B cells in peripheral lymph nodes of the anti-IgD-treated mice causes the low responsiveness to i.p. immunization, but that the IgD- B cells in the spleen are quite able to respond and are, in fact, more responsive than IgD+ B cells. This increased responsiveness, together with the higher IgM/IgG ratios for all Ig isotypes and an otherwise similar order of isotype distribution (gamma 1 greater than gamma 2b greater than gamma 2a = epsilon greater than or equal to alpha) as in controls, suggests that a hyperresponsive, but less mature IgD- B cell population is selectively produced in the spleens of mice treated with anti-IgD from birth.