ANALYSIS OF CHICKEN CD4 BY MONOCLONAL-ANTIBODIES INDICATES EVOLUTIONARY CONSERVATION BETWEEN AVIAN AND MAMMALIAN-SPECIES

We have created a panel of mouse monoclonal antibodies detecting diffe rent epitopes on avian CD4 molecule. Two-color immunofluorescence anal ysis shows that chicken peripheral alphabeta T cells are either CD4 or CD8 single positive whereas most gammadelta T cells are CD4-negative both in the thymus and peripheral tissues. Unlabeled antibody competit ion analysis by flow cytometry demonstrates that several different epi topes on chicken CD4 are recognized by these antibodies. Antibodies pr ecipitate a monomeric glycoprotein from surface-labeled chicken thymoc ytes and T cells with relative molecular mass (M(r underbar)) of 64 kd as analyzed by SDS gel electrophoresis. Removal of N-linked carbohydr ates by endoglycosidase-F increases the electrophoretic mobility and r eveals the core protein size with M(r underbar)) of 45 kd. The anti-CD 4 antibodies inhibit antigen-induced cellular proliferation of a keyho le limpet hemocyanin (KLH) -specific T cell line. They synergize in th e blocking of T cell proliferation with anti-class II major histocompA tibility complex (MHC) -specific antibodies indicating that chicken CD 4 is involved in antigen recognition process by CD4+ T cells. We also show that chicken CD4 is down-modulated in a similar manner as its mam malian equivalent when thymocytes are stimulated in vitro with phorbol esters. Altogether these findings suggest functional and biochemical conservation of the CD4 molecule in evolution.