The detailed distribution of MHC Class II antigens in normal human organs.

In a previous article we described the detailed tissue distribution of MHC class I antigens. In this study, we have used a monoclonal antibody, NFK1, to study the tissue distribution of MHC class II antigens. This antibody, which detects a monomorphic determinant common to the DR, SB, and DC molecules, was used to stain frozen sections of normal tissues from throughout the human body by a sensitive peroxidase-antiperoxidase immunohistological technique. Although previous studies, both in animal models and in human beings, have shown that class II antigens are expressed on a limited number of nonlymphoid tissues, our study has extended the spectrum of tissues on which this class of antigens is detectable. Epithelial cells in a number of organs were positively stained--these include the tongue, tonsils, epiglottis, trachea, small intestine, urethra, epididymis, and proximal renal tubules. Lymphatics throughout the body appeared to express class II antigens. Capillaries in brain, testis, and placenta appeared not to express class II antigens, but in the rest of the body they showed strong and uniform staining. These and other observations, and their implications, are discussed in relation to previously published studies.