HUMAN SURFACTANT PROTEIN-A CONTAINS BLOOD GROUP-A ANTIGENIC DETERMINANTS

A major blood group antigenic epitope was identified on human pulmonar y surfactant protein A (SP-A). MAb and polyclonal antibodies generated against purified human SP-A aggregated blood group A human erythrocyt es and immunostained epithelial cells in a variety of human tissues, c onsistent with the tissue distribution of major blood group antigens. SP-A MAb (MAb-8) agglutinated red cells and immunostained tissues from A or AB blood groups, but did not react with cells or tissues from O or B individuals. MAb-8 immunostaining of tissue from blood group A in dividuals was ablated by incubation with blood group A red cells. MAb and polyclonal antibodies directed against A blood group antigens reac ted strongly with purified SP-A obtained from a blood group A individu al with alveolar proteinosis. MAb and polyclonal antibodies specific f or B blood group antigen failed to react with SP-A from this patient o r from patients who were in blood group B. Reactivity of anti-blood gr oup MAb was lost after treatment of SP-A with endoglycosidase-F, demon strating its reactivity with an epitope dependent on the asparagine-li nked oligosaccharide at asparagine 187. Reactivity of MAb-8 with SP-A persisted after endoglycosidase-F treatment, but was lost after digest ion with collagenase as assessed by Western blot after SDS-PAGE. React ivity of MAb to SP-A was sensitive to beta-elimination, supporting the presence of another blood group antigenic site distinct from the epit ope dependent on the asparagine-linked carbohydrate. The finding that the SP-A molecule contains a major blood group epitope has implication for the clinical use of surfactant replacement preparations and diagn ostic reagents based on this protein.