CD19 is a substrate of the antigen receptor-associated protein tyrosine kinase in human B cells.

The B cell antigen receptor, mIg, is part of a multimolecular complex including Ig alpha, Ig beta, and CD19. We provide evidence here that upon ligation of mIg CD19 becomes phosphorylated on tyrosine residues. Further, protein tyrosine kinase lyn, which is activated by the antigen receptor, can be readily co-immunoprecipitated with CD19 suggesting this is the enzyme responsible for the antigen receptor mediated tyrosine phosphorylation of CD19.