Abstract:

The effect of proteases and of extracts of human blood leukocytes and platelets on the sensitization of human red blood cells (RBC) by lipopolysaccharides (LPS) and by the cell-sensitizing factor (SF) of group A streptococci, as determined by passive hemagglutination, was studied. While treatment of RBC by trypsin, papain (10-1500Μg/ml), and plasmin markedly increased the binding of SF to RBC as determined by the passive hemagglutination test, small amounts of leukocyte and platelet extracts (25Μg protein) failed to enhance the sensitization of RBC. On the other hand, high concentrations of leukocyte extracts (>250Μg protein) destroyed, to a large extent, the capacity of SF to sensitize RBC. The inhibitory effect of the leukocyte extracts on the SF system was optimal at neutral pH and was inhibited by heat treatment, by phenylmethyl sulfonyl fluoride (PMSF), and by liquoid, indicating the participation of neutral proteases in this reaction. Treatment of LPS with small amounts of leukocyte extracts activated the LPS molecule; this treatment could replace the alkaline treatment needed to enhance the capacity of LPS to sensitize RBC. Very high hemagglutination titers were, however, obtained when both LPS and RBC were simultaneously treated with leukocyte extracts (25Μg protein). On the other hand, larger amounts of extracts destroyed receptors for LPS on RBC. Both the enhancing and destroying capacities of the leukocyte enzyme on the LPS system were abolished by PMSF. The simultaneous sensitization of RBC by SF and LPS showed that SF is a more dominant sensitizing agent. Histone blocked receptors in RBC for both SF and LPS. The effect of the histone was abolished by trypsin. Histone also strongly bound LPS and SF and abolished to a large extent their cell-sensitizing properties. The possible role played by leukocyte extracts in the initiation of tissue damage induced by cell-sensitizing products of bacteria is discussed.