Endocytosis of CD4 in Lymphoid and Non-Lymphoid Cells

Abstract

The lymphoid differentiation antigen CD4 is a glycoprotein which binds to non-polymorphic regions on MHC class II molecules and is expressed primarily on helper/inducer T-lymphocytes and on some cells of the macrophage/monocyte lineage. CD4 is involved in T-cell ontogeny in the thymus and in the activation of peripheral blood lymphocytes (Robey and Axel, 1990). The specific association of CD4 with the cytoplasmic protein tyrosine kinase p56^lck (Turner et al., 1990) suggests that CD4 may be directly involved in signal transduction. In addition CD4 is used as a receptor by the human immunodeficiency viruses HIV-1 and 2. In order to gain a better understanding of the mechanisms underlying the normal function of CD4 in T-cells and in the pathway of HIV entry, we have studied the endocytic trafficking of CD4 in non-lymphoid cells transfected with the CD4 gene and in a number of leukaemia/lymphoma-derived T-cell lines.