Organ-specific distribution of major histocompatibility antigens in rats

The present study systematically investigated the expression and distributi on of the major histocompatibility complex (MHC) classes I and II in the ra t. About 150 native tissue probes from eight adult Lewis rats were taken, r epresentative for most organs, tissues, and the vascular system. MI-IC expr ession was analyzed by two monoclonal antibodies (mAb) generated against th e non-polymorphic determinants of rat MHC class I (Ox-18) and class II (Ox- 6). Immunoreactivities were compared to those of different endothelial (HIS 52, TLD-3A12, Ox-43, REHA-1 antigen), histiocytic (ED1, ED2), B-cell (RLN-9 D3), and T-cell (MRC Ox-52) markers. A nonspecific mAb (MR12/53) served as a negative control. Pretested concentrations on various tissues and the alk aline phosphatase-anti-alkaline phosphatase technique allowed semiquantitat ive evaluation of serial cryostat tissue sections. MHC class I expression w as detected on most immunocompetent cells. Endothelial cells were stained h eterogeneously along the vascular system and the organ-specific microcircul ation. Furthermore, some organs showed staining of parenchymal cells. MHC c lass II was found on all immunocompetent cells positive for the B-cell mark er and about 15% of cells positive for the histiocytic markers. Besides the well-known expression of MHC class II in the outer zone of the renal proxi mal tubule, further organ-specific cell forms were found positive. In concl usion, the present study outlines tissue-specific distribution of MHC I/ II and implies that each organ carries a variable immunologic burden that nee ds to be considered for any transplantation model.