Defective B cell responses in the absence of SH2D1A

2016

The Journal of Immunology, 2002

Grb2-associated binder 1 (Gab1) is a member of the Gab/daughter of sevenless family of adapter molecules involved in the signal transduction pathways of a variety of growth factors, cytokines, and Ag receptors. To know the role for Gab1 in hematopoiesis and immune responses in vivo, we analyzed radiation chimeras reconstituted with fetal liver (FL) cells of Gab1 ؊/؊ mice, because Gab1 ؊/؊ mice are lethal to embryos. Transfer of Gab1 ؊/؊ FL cells of 14.5 days post-coitum rescued lethally irradiated mice, indicating that Gab1 is not essential for hematopoiesis. Although mature T and B cell subsets developed normally in the peripheral lymphoid organs, reduction of pre-B cells and increase of myeloid cells in the Gab1 ؊/؊ FL chimeras suggested the regulatory roles for Gab1 in hematopoiesis. The chimera showed augmented IgM and IgG1 production to thymus-independent (TI)-2 Ag, although they showed normal responses for thymus-dependent and TI-1 Ags, indicating its negative role specific to TI-2 response. Gab1 ؊/؊ splenic B cells stimulated with anti-␦-dextran plus IL-4 plus IL-5 showed augmented IgM and IgG1 production in vitro that was corrected by the retrovirus-mediated transfection of the wild-type Gab1 gene, clearly demonstrating the cell-autonomous, negative role of Gab1. Furthermore, we showed that the negative role of Gab1 required its Src homology 2-containing tyrosine phosphatase-2 binding sites. Cell fractionation analysis revealed that nonfollicular B cells were responsible for the augmented Ab production in vitro. Consistent with these results, the Gab1 gene was expressed in marginal zone B cells but not follicular B cells. These results indicated that Gab1 is a unique negative regulator specific for TI-2 responses.

2004

The Journal of Immunology, 2004

Immunity, 1999

Pao et al., 1998). The † Laboratory for Lymphocyte Signaling consensus of these experiments is that tyrosine phos-Institute for Genetics phorylation of ITAMs is required for the induction of University of Cologne protein tyrosine phosphorylation and calcium mobiliza-Weyertal 121 tion. In one study (Flaswinkel and Reth, 1994) using the D-50931 Cologne J558L myeloma cell line, mutant Ig-␣ molecules were Germany tested in the context of a complete BCR. The ability to ‡ Basel Institute for Immunology activate PTKs and induce tyrosine phosphorylation was Grenzacher Strasse 487 severely reduced in cells expressing Ig-␣ molecules with CH-4005 Basel a truncated cytoplasmic tail or an ITAM in which both Switzerland tyrosines were changed to phenylalanine, even in the presence of endogenous Ig-␤. Transgenic and gene targeting experiments in mice Summary have demonstrated the importance of Ig-␣ and Ig-␤ for B cell development in vivo. Either Ig-␣ or Ig-␤ chimeric To study the function of Ig-␣ in the selection of autoremolecules expressed as transgenes have been suffiactive B cells, we have analyzed mb-1 cytoplasmic cient for supporting steps in B cell maturation and inductruncation mutant mice (mb-1 ⌬c/⌬c), which coexpress ing allelic exclusion (Papavasiliou et al., 1995a, 1995b; transgenes encoding hen egg lysozyme (HEL) and Teh and Neuberger, 1997). In Ig-␤ knockout mice, a com-HEL-specific immunoglobulin. We demonstrate that plete block in B cell development at the pro-B cell stage in the presence of soluble HEL (sHEL) and dependent was observed, probably because the BCR cannot reach on the mb-1 ⌬c mutation, most immature B cells bearing the cell surface in the absence of Ig-␣/Ig-␤ heterodimer the HEL-specific Ig transgene undergo rearrangements formation (Gong and Nussenzweig, 1996). mb-1 ⌬c/⌬c mice of endogenous light chains, resulting in loss of HEL express a truncated Ig-␣ protein that lacks the ITAM specificity. Moreover, immature B cells from Ig-␣ muand has a cytoplasmic tail that consists of 20 instead tant mice respond to BCR cross-linking with an exagof 61 amino acids (Torres et al., 1996). B lymphocytes gerated and prolonged calcium response and inducin mb-1 ⌬c/⌬c mice are compromised in their development tion of protein tyrosine phosphorylation. Our data resulting in a 2-to 4-fold reduction in the number of imply a negative signaling role for Ig-␣ in immature B pre-and immature B cells in the bone marrow and a cells. drastic 100-fold decrease of mature B lymphocytes in the spleen. Moreover, it was demonstrated that mature Introduction B cells are dependent on Ig-␣-mediated signals to mount an immune response to a T-independent antigen The B cell antigen receptor complex (BCR) transmits (Torres et al., 1996). In the present study, we further signals that regulate the survival, differentiation, proliferevaluate the signaling function of Ig-␣ in the hen egg ation, and migration of B lymphocytes (Rajewsky, 1996; lysozyme (HEL) transgenic mouse model (Goodnow et Reth and Wienands, 1997; Healy and Goodnow, 1998). al., 1988) to determine the impact of Ig-␣ on positive The signaling function of the BCR has been ascribed to versus negative signaling. mb-1 ⌬c/⌬c mice were generthe mIg associated Ig-␣ and Ig-␤ (CD79a/CD79b) heteroated expressing HEL-specific Ig (Ig HEL) alone or coexdimers that are encoded by the genes mb-1 and B29, pressing either soluble (sHEL; Goodnow et al., 1988) or respectively. Both Ig-␣ and Ig-␤ contain a single immumembrane bound HEL (mHEL; Hartley et al., 1991), to noreceptor tyrosine-based activation motif (ITAM), a study whether tolerance induction either by "anergy" common motif found also in the receptor complexes of or clonal deletion was still operational. One might also other cells in the immune system including T, NK, and envision that the expression of the transgenic anti-HEL mast cells (Reth, 1989; Cambier 1995a). BCR crossreceptor on its own or in combination with HEL might linking leads to the activation of protein tyrosine kinases overcome the developmental block observed in mb-(PTKs) and subsequently to the phosphorylation of the 1 ⌬c/⌬c mice and lead to antigen-driven maturation of B two ITAM tyrosines (reviewed in Cambier, 1995b; Reth lymphocytes. Our data demonstrate that autoreactive and Wienands, 1997). These phosphorylated tyrosine B cells or their receptors are more efficiently counterseresidues represent binding sites for Src homology 2 lected in mb-1 ⌬c/⌬c than in wild-type mice and suggest (SH2) domain-containing proteins including Src family that this is due to hyperresponsiveness of mutant cells protein tyrosine kinases and Syk (Clark et al., 1992; to BCR cross-linking. Johnson et al., 1995). In several studies with Ig-␣ and Ig-␤ chimeric molecules expressed in B cell lines, the Results In order to examine how an Ig-␣ cytoplasmic truncation