We and others have shown that mice lacking the myeloid Src-family kinases Hck, Fgr, and Lyn,115 the Syk tyrosine kinase,120,121 the PLCγ2 phospholipase99,122 or the Vav1, Vav2, and Vav3 exhange factors122 are completely protected from arthritis development in the K/BxN serum-transfer model. Here, FGR is linked to arthritic joint disease.