Tyrosine phosphorylation after FcαR cross-linking is reduced in transfectants with altered γ chain.

(A) Transfectants expressing FcαR and either WT γ chain (WT), γ chain with IIA ITAM (IIA), or γ chain with Y → F mutation (Y → F) were treated as follows: (1) medium, (2) anti-mIgM, and (3) anti-FcαR IgM mAb + anti-IgM. Tyrosine phosphorylation in whole-cell lysate was detected by SDS-PAGE and Western blot analysis with antiphosphotyrosine. Three separate experiments yielded similar results. (B) Prior to immunoblotting with antiphosphotyrosine, the same nitrocellulose membrane shown in panel A was stained with ponceau red to ascertain equivalent loading. Details of the above are described in “Materials and methods.”