FUNCTIONAL EXPRESSION OF THE MHC CLASS I-RELATED RECEPTOR, FCRN, IN ENDOTHELIAL-CELLS OF MICE

Our recent data indicate that the MHC class I-related receptor, FcRn, plays a role in regulating serum IgG levels, in addition to its known role in transferring IgG from mother to young. In the current study, t he distribution of FcRn in adult mice has been investigated using seve ral approaches. First, tissue distribution of anti-FcRn F(ab')(2), mur ine IgG1 and recombinant, lgG1-derived Fc-hinge fragments has been ana lyzed, and these FcRn binding proteins localize predominantly in skin and muscle with lesser amounts in liver and adipose tissue. Second, hi stochemical analyses of muscle and liver with anti-FcRn F(ab')2 indica te that FcRn is expressed in the endothelium of small arterioles and c apillaries, but not in larger vessels such as the central vein and por tal vasculature, Third, immunoprecipitation and immunofluorescence stu dies of cultured murine endothelial cells show that functional FcRn is expressed in these cells, and is located within vesicular structures in the cytosol and not on the membrane. Taken together the data demons trate that FcRn is expressed in functionally active form in endothelia l cells, indicating that these cells are a possible site at which seru m IgG homeostasis is maintained.