• Cellular and molecular studies of marginal zone B cells

      Song, Haifeng; Cerny, Jan, 1939- (2003)
      Marginal zone (MZ) B cells are the major cell population in the spleen to respond to T-independent type II antigens (Ti-II) in the blood. However, the evidence regarding the potential role of MZ B cells in response to T-dependent Ag (Td-Ag) is still rudimentary and somewhat controversial, as studies with Pyk-2-/- and RBP-J conditional deficient mice showed opposite results. The current study compared in detail, the responses of MZ and follicular (FO) B cell to a Td Ag, Nitrophenyl-hapten (NP) coupled to chicken gamma globulin (NP-CGG) in an adoptive transfer experiment. The results showed that MZ B cells are the major population to generate early antibody-forming cells (AFC) and they produce about 10-fold higher IgM and slightly higher IgG throughout the entire primary response observed (3 months) compared to FO B cells. In addition, MZ B cells gave rise to germinal center (GC) formation albeit with a delayed onset. GCs from both MZ and FO B cells displayed similar levels of somatic hypermutation (SHM) frequencies, clonal selection, and IgG memory responses. Surprisingly, MZ B cells also produced an IgM memory response. The VH gene repertoire of the early antibody forming cells (AFCs) from MZ B cells is different from that of GCs and late AFCs, suggesting their origins from different precursors. Studies on gene expression profile showed that MZ B cells express some early activation markers both on cell surface, such as B7-2, CD54, and CD44, and intracellularly, such as c-myc, pim-1, and fos proteins, consistent with their rapid response to stimulation. Most importantly, MZ B cells upregulate gene expression of the Blimp-1, which confers MZ B cells the propensity to rapidly develop into plasma cells. In addition, MZ B cells differentially express higher levels of RP105, a LPS receptor on B cells, which may explain the stronger response of MZ B cells to LPS stimulation and the predominant role in Ti responses. In conclusion, MZ B cells are phenotypically and functionally heterogeneous and they have the potential to respond to both Ti and Td Ags.
    • The gut environment obviates obligatory signals for germinal center formation and somatic hypermutation in the Peyer's patches

      Basu, Subhendu; Cerny, Jan, 1939- (2003)
      Germinal center (GC) reaction and somatic mutation in the spleen in response to protein antigens is absolutely dependent on help from antigen-specific CD4+ T lymphocytes and stimulation of B cells via the CD19 co-receptor. However, the absence of CD4 T cell help apparently does not abrogate the GC formation in the Peyer's patch. The present study makes use of normal, CD4-null and CD 19-null mice to test the hypothesis that activation of somatic mutation in P. patch is independent of conventional co-stimulation. Splenic GC were induced by immunization with the hapten, nitrophenyl coupled to a protein carrier. The GC B cells were micro-dissected from tissue sections and the rearranged Vlambda1Jlambda1 genes were amplified and sequenced. The CD4-null and CD19-null mice failed to form GC in the spleen but the GC in the P. patches of these mice were comparable in number and average mutation frequency to antigen-driven splenic GC in the normal mice. It was determined that the GC formation in the P. patches was dependent on help from alphabeta T cells and that gammadelta T cells were not involved in providing this help. Adoptive transfer of the splenic T cells from CD4-null mice into T deficient mice resulted in GC formation in the P. patch but not in the spleen. Therefore, the presence of GC in the P. patch of CD4-null mice was not due to a special T cell population but a function of the unique gut environment since the splenic T cells can provide the requisite help for GC formation when present in the P. patch. It is apparent that obligatory stimuli for splenic GC formation and somatic mutation are dispensable in P. patches.