Ibrutinib and idelalisib block BCR-induced LCP1 serine-5 activation. Immunoblot analysis of freshly obtained primary CLL cells either pretreated with 1 µM ibrutinib or continuously treated with 1 µM idelalisib and stimulated for 15 minutes with plate-bound anti-IgM. Control samples included DMSO-treated cells and matching unstimulated samples. Immunoblots were probed for pSer5-LCP1, total LCP1, pErk, and total Erk. Densitometry measurements indicate intensity relative to total protein controls. Immunoblot is representative of 3 independent experiments performed on different CLL donors.