Intravenous injection of killed Corynebacterium li- quefaciens induced a population of red blood cells that expressed both H-2K and H-2D antigens at exceptionally high density and displayed augmented immunoge- nicity for H-2 alloantigen-specific B cell activation. Injection of killed Escherichia coli or E. coli lipopolysac- charide was ineffective for the generation of such RBC. RBC that express H-2 antigens at high density first appeared at 7 days after injection of C. liquefaciens. These RBC persisted for more than 50 days, although they lost H-2 antigens gradually with time. The observed phenomenon was not due to enhanced erythro- poiesis and peripheral release of immature RBC (reticulocytes); populations of both mature and immature RBC of mice injected with C. liquefaciens expressed H- 2 antigens at high density, whereas those from normal mice or mice injected with phenyl hydrazine did not. Appearance of RBC expressing H-2 antigens at high density was preceded by a temporal increase in H-2 expression of bone marrow cells that included precursors of RBC. It was concluded that RBC expressing H-2 antigens at high density were descendants of bone marrow cells whose H-2 expression was augmented by C. liquefaciens. The present communication would be the 1st report of the bacteria-mediated augmentation of cell surface expression and activity of major-histocompati- bility-compex class I antigens on host cells in vivo.
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