TCB 1996 6:359-366 Reactivity of 62 Rh MAbs with weak and variant antigens F. MORELATI, N. REVELLI, F. DRAGO, P. MANCUSO, G. SIRCHIA Centro Trasfusionale e di Immunologia dei Trapianti, IRCCS Ospedale Maggiore, Milano, Italy Summary We characterized serologically 5 anti-C (4 IgM and 1 IgG), 3 anti-c (2 IgM and 1 IgG), 4 anti-E {1 IgM and 3 IgG), 4 anti-e {3 IgM and 1 IgG) and 46 anti-D (16 IgM and 30 IgG) monoclonal antibodies, provided by the Rh Section of the Third International Workshop and Symposium on Monoclonal Antibodies against Human Red Blood Cells and Related Antigens {1996) for their ability to detect weak and variant antigens. The agglutination patterns were esta- blished using untreated and papain-treated red blood cells in a column agglutination technology system (BioVue, Ortho). Signifi- cant differences were found between the IgM and IgG antibodies. The papain treatment seemed to be important for IgM but not for IgG antibodies. Almost all of the IgM anti-D antibodies detected untreated D Iv samples and almost all of the IgG anti-D antibodies detected untreated weak D samples. Both IgM and IgG anti-D anti- bodies showed the highest number of negative reactions with Dw and Rh 33 red blood cells. The Cwc w sample was detected by only one of the 4 anti-C IgM MAbs using enzyme4reated red blood cells. All anti-c MAbs were able to detect treated Cx samples. Because of the small number of weakly expressed E and e samples, definitive conclusions cannot be drawn on the ability of these antibodies to detect these antigens. Keywords: Column agglutination technology, monoclonal anti-D, Rh D antigen, Rh D epitopes. Introduction The aim of this study was to establish the reactivity of Rh monoclonal antibodies, provided by the Rh Section of the Third International Workshop and Symposium on Monoclonal Antibodies against Human Red Blood Cells and Related Antigens (1996) using column agglutination technology and a panel of weak and variant phenotypes. Correspondence to: Fernanda Morelati,B. Sc.,CentroTrasfusionale e di Immunologia dei Trapianti, IRCCSOspedale Maggiore,via F. Sforzan. 35, 20122 Milano, Italia. Materials and methods Monoclonal antibodies The following monoclonal antibodies (MAbs} were made available to us through the Workshop: 5 anti-C {4 IgM and 1 IgG), 3 anti-c {2 IgM and 1 IgG), 4 anti-E {1 IgM and 3 IgG), 4 anti-e (3 IgM and 1 IgG} and 46 anti-D {16 IgM and 30 IgG}. The MAbs were used neat and in 1/10 and 1/100 dilutions with 2% bovine serum albumin {Sigma Chemical Company, St. Louis, 359