正常ヒト末梢血単核球膜表面のＨＳＣ７０蛋白質について

Abstract

71kDa heat shock cognate protein (HSC70) is a member of the Hsp70 family and is constitutively expressed in organisms as diverse as slime molds, bacteria, plants and higher eukaryotes. Proteins in the Hsp70 family are known as chaperones that involve quality control of cellular proteins, folding of nascent polypeptide chains and trafficking of proteins via membrane structure. Recently, it was revealed that Hsp/HSC70 proteins were presented on surface of virus- or bacteria-infected cells, immortalized cells and blood cells of autoimmune disease patients. We previously reported that the HTLV-1 receptor consists of HSC70, β-actin and phosphatidylglycerol on the surface of MOLT-4 cells. In this study, we examined the induction of HSC70 protein on the surface of peripheral blood mononuclear cells (PBMCs) from healthy individuals. Little HSC70 protein was observed on the surface of PBMCs before cultivation. However, after 72 hours culture, 41±9.1% of PBMCs presented HSC70 proteins on the cell surface. On the other hand, in culture with phytohemagglutinin (PHA), 70±14% of PBMCs exposed HSC70 protein on the cell surface after 24 hours, and 84±5.0% after 72 hours. PHA stimulated the presentation of HSC70 protein on the cell surface of CD4+ T cells, which are the target cells of HTLV-1 in vivo, as well as that on the surface of PBMCs. Susceptibility to HTLV-1 of target cells was parallel to the expression level of HSC70 molecules on the cell surface. These results demonstrate that HSC70 protein on the surface of PBMCs and CD4+ T cells exposes the domains which are functional for HTLV-1 infection, and that stimulation by cultivation and mitogen enhances the trafficking of HSC70 proteins to the surface of plasma membrane. This is the first finding that HSC70 on the surface of CD4+ T cells functions as a receptor for cell-to-cell transmission of HTLV-1.