On FFPP mouse muscles: I used Sigma MY32 ( MHC Type II) . For me, it works without Ag unmasking, but patchy. With citric pH6 unnmasking got a paler result but not patchy. TRIS pH 10 solution may well be better. For type I MHC, I used MAB1628, from Chemicon. Again plus Citric pH6 unmasking( can try TRIS pH10 )