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Surface IgM‐stimulated proliferation, inositol phospholipid hydrolysis, Ca2+ flux, and tyrosine phosphorylation are not altered in B cells from p59
fyn‐/‐ mice

The surface immunoglobulin M (sIgM)‐associated src family protein tyrosine kinases (PTKs) p55 blk , p59 fyn , and p53/56 lyn become activated in B cells within seconds following sIgM cross‐linking. Studies using protein tyrosine kinase (PTK) inhibitors have demonstrated that PTK activity is crucial for downstream events such as calcium flux, inositol phospholipid hydrolysis, and cell cycle entry. The roles that the individual src family PTKs play in sIgM signaling are largely unknown, however. In order to determine whether p59 fyn plays a distinct role in sIgM signal transduction, the signaling capabilities of B cells isolated from fyn “knockout” mice were evaluated. We observed that in the absence of p59 fyn , there was no demonstrable compromise of the slgM‐coupled signaling events measured (tyrosine phosphorylation, inositol phospholipid hydrolysis, and Ca2+ flux). We propose that either p59 fyn is not involved in coupling sIgM to these specific signaling pathways or that other PTKs are able to compensate for the absence of p59 fyn , indicating redundancy in the sIgM signaling pathways. J. Leukoc. Biol. 56: 812–816; 1994.