| Popis: |
WEHI-231 is a murine B cell lymphoma that has been used extensively as a model for the immature stage B cell and its functional response to Ag receptor cross-linking as a model for immature B cell tolerance. This cell line expresses sIgM, CD5, and FcR gamma, but lacks the B cell-specific isoform of CD45 (B220). This study demonstrates for the first time that WEHI-231, in contrast to classically defined immature B cells, expresses delta on its surface. Analysis of delta on WEHI-231 revealed structural differences with respect to that on BAL-17 or primary splenic B cells. Although the m.w. of delta on the latter two B cell populations was similar, delta on WEHI-231 manifested a marked increase in its apparent m.w. deduced by SDS-PAGE. This difference was found to be due primarily to differential N-linked glycosylation. Signal transduction through the endogenous sIgD on WEHI-231 was investigated. In contrast to cross-linking of sIgM, cross-linking of the endogenous surface IgD on WEHI-231 was unable to generate a negative growth response in these cells. This inability may be due to uncoupling from normal surface Ig signaling pathways. The signaling properties of the endogenous sIgD on WEHI-231 differ from that on primary B cells and other sIgD-expressing cell lines. Whereas sIgD on splenic B lymphocytes or the mature B cell line BAL-17 is coupled to inositol phospholipid hydrolysis and calcium mobilization, cross-linking of sIgD on WEHI-231 failed to elicit these events, although induced changes in tyrosine phosphorylation were observed. Thus, endogenous expression of surface IgD on WEHI-231 is inconsistent with its representing the classically defined immature stage B cell. The structural and signaling differences associated with delta on these cells suggest the potential for developmentally regulated delta function and model for study of sIgD signal transduction. |
