Graft-versus-host disease induces expression of Ia antigen in rat epidermal cells and gut epithelium

Ia antigens are polymorphic membrane-bound glycoproteins coded for by genes of the major histocompatibility complex. It has been shown that these genes are linked to Ir (immune response) genes that determine the level of antibody responses made by an individual to specific antigens 1 . For this reason, and because of the requirement for I-region identity between antigen-presenting cells and T cells for their effective interaction 2 , Ia antigens are thought to play a part in antigen recognition by the immune system and it has been suggested that the Ia antigens are products of the Ir genes 1 . In general the tissue distribution of Ia antigens is consistent with this view as they have been shown to be present on B cells, activated T cells and macrophages 3 and on cells other than lymphocytes in spleen, lymph node and thymus 4,5 . However, it has been shown that Ia antigens are also present on epithelial cells of the gut, kidney, bronchi 6,7 and mammary gland 8 . The significance of Ia antigens in tissues of nonimmune function is not understood. However, it is clear that Ia expression shows some lability in that macrophages 9 , T cells 3 and mammary gland 8 may all change from expressing little or no Ia to being strongly Ia-positive when appropriately stimulated. Here we show that when a systemic graft-versus-host response is induced in rats, the epidermal layer of the skin and the epithelium of the small and large intestine express large amounts of Ia antigen.