CELLULARIMMUNOLOGY 122,164-177 (1989) Lack of a Role of Monocytes in the lnhibition by Monoclonal Antibodies to Monomorphic and Polymorphic Determinants of HLA Class I Antigens of PHA-P-Induced Peripheral Blood Mononuclear Cell Proliferation’ MARIO DE FELICE,* MARIA CATERINA TURCO,* LAURA CORBO,* PATRIZIA CARANDENTE GIARRUSSO,~ ANNALISA LAMBERTI,~ GIULIANA VALERIO,? MASSIMO TEMPONI,$ FRANCESCO COSTANZO,*,~ SOLDANO FERRONE,~~ AND SALVATORE VENUTA* *Istituto di Oncologia Clinica e Sperimentale, Facolia di Medicina e Chirurgia di Catanzaro, Universiia di Reggio Calabria, Catanzaro, Italy; tDipartimento di Scienze Biochimiche e Biotecnologie, II Facolfa di Medicina e Chirurgia, Universiia di Napoli, Napoli, Italy; and SDepartment of Microbiology and Immunology New York Medical College, Valhalla, New York 10595 Received February 21, 1989; accepted April 18, 1989 This study aimed at characterizing the mechanism(s) underlying the regulatory role of distinct determinants of HLA Class I antigens in PHA-P-induced T cell proliferation and the involve- ment of monocytes in this phenomenon. The anti-HLA-A2,A28 monoclonal antibodies (MoAb) CR 1 l-35 1, the MoAb Q6/64 to a determinant restricted to the gene products of the I antigensHLA-B locus, and the MoAb CR 10-2 15 and W6/32 to distinct monomorphic determi- nants of HLA Class I antigens were found to inhibit PHA-P-induced peripheral blood mononu- clear cell (PBMC) proliferation in a dose-dependent fashion. The inhibition is specific and re- flects neither inhibition of PHA-P binding to cells nor a toxic effect of the anti-HLA Class I MoAb. The latter differed in the concentration required to induce inhibition, in the influence of the concentration of PHA-P used as mitogen, in the differential effect on the donors used as a source of PBMC, and/or in the requirement of the Fc portion to induce inhibition. At variance with the information in the literature, the inhibitory effect of anti-HLA Class I MoAb on PHA- P-induced PBMC proliferation neither reflected their interaction with accessory cells nor was mediated by suppressor factors released by monocytes stimulated with PHA-P in the presence of anti-HLA Class I MoAb. Therefore, the regulatory role of HLA Class I antigens in T cell proliferation is not likely to be mediated by monocytes and/or factors released from them, but may reflect an involvement of these molecules in T cell activation pathways. 0 1989 Academic Press. Inc. INTRODUCTION There is general agreement that HLA Class I antigens regulate T cell proliferation induced via the CD2 and CD3 pathways ( 1- 13). Distinct determinants of HLA Class ’ The work presented in this paper was supported by Grants CNR PF Oncologia (86.00607.44) and PF Ingegneria Genetica e Basi Molecolari delle Malattie Ereditarie (86.00103.5 1) by the Italian Association for Cancer Research and by National Institutes of Health Grants AI2 1384 and CA39559. 2 To whom correspondence and reprint requests should be addressed. 164 0008-8749189 $3.00 Copyright 0 1989 by Academic Press, Inc. All rights ofreproduction in any form reserved