Vol. 152, No. 3,1988 May 16,1988 BIOCHEMICAL AND BIOPHYSICALRESEARCH COMMUNICATIONS Pages 95]-956 DEPLETION OF PROTEIN KINASE C INDUCED BY AN ANTI HLA CLASS I MONOCLONAL ANTIBODY IN PHYTOHEMAGGLUTININ ACTIVATED HUMAN T CELLS Licia Poltronieri*, Edon Melloni**, Michele Rubini*, Rita Selvatici*, Cristina Mazzilli***, Roberto Baricordi* and Enrico Gandini* *Istituto di Genetica Medica, Universit& degli Studi di Ferrara, Ferrara, Italy **Istituto Policattedra di Chimica Biologica, Universit~ degli Studi di Genova, Genova, Italy ***Dipartimento di Biologia Sperimentale, Universit~ La Sapienza, Roma, Italy Received March 22, 1988 SUMMARY: Anti HLA Class I Monoclonal Antibody depletes Protein Kinase C (PKC) to 20% of control value in PHA activated human T cells. The effect is reversible: in 24 hours the enzymatic activity returns to 58% of control value. Removal of antibody from the culture medium increases the rate of recovery. Implications of this finding for the modulation by HLA Class I antigens of the proliferative response of T cells to lectins are discussed. ® 1988 Academic Press, Inc. Gene products encoded in the Major Histocompatibility Complex (MHC) play a central role in immune response in man, as in other animal species. Class I antigens are involved in cytolytic T lymphocyte (CTL) response as shown for H2K/H2D antigens in the mouse (i) and for HLA A and B antigens in human (2,3,4,5), whereas MHC Class II antigens are largely involved in antigen presentation and antigen specific interactions between T cells and macrophages (6). Furthermore antibodies to MHC Class I Abbreviations: PKC, protein kinase C; PHA, phytohemagglutinin; FCS, fetal calf serum; MoAb, monoclonal antibody; PMA, phorbol 12-myristate 13-acetate; PMBC, peripheral mononuclear blood cells; SRBC, sheep red blood cells. 951 0006-291X/88 $1.50 Copyright © 1988 by Academic Press, Inc: All rights of reproduction in any form res#rved.