Expression of human blood group antigens A and B in stomach cells of C. carpio, C. auratus, R. ridibunda and H. sapiens.

: Human blood group ABH antigens are found not only on red blood cell membranes, but in many other cell types as well. Their biological functions still remain unclear. The aim of the present study was to examine the cellular expression of these antigens in the stomach of representatives of different Vertebrates--Pisces and Amphibia and to compare it with their expression found in Man. The immunohistochemical technique applied was based on the biotinstreptavidin-peroxidase complex. Monoclonal antibodies to human A and B antigens were used as primary antibodies in the system. Stomach paraffin sections from Cyprinus carpio, Carassius auratus, Rana ridibunda and Homo sapiens were examined. Blood group antigens were found mainly in tunica mucosa of C. carpio, C. auratus and R. ridibunda. Tunica muscularis and tunica serosa were always immunonegative. The antigens were localized in the apical part of the cytoplasm of epithelial cells in lamina epithelialis. Strong positive reaction was seen in secretory granules of the stomach of C. auratus, while in R. ridibunda the antigens were expressed by single epithelial cells in cardial stomach glands. A and B antigens were not found in human stomach sections most probably due to the negative secretor status of the individuals studied. Our results show that ABH human blood group antigens are evolutionary conserved structures similarly expressed by different Vertebrates. The phylogenetic stability in their cellular expression possibly results from the important biological role they have. Future large scale systematic investigations could elucidate the undefined and disputable physiological functions of human blood group antigens.