Hemolysis and suppression of neutrophil chemotaxis by a low molecular weight component of human burn patient sera

Abstract

During the past year, we have reported the isolation and characterization of a low molecular mass (less than 5000 Da) complex (SAP), having profound immunosuppressive activity, found in the plasma of patients with major thermal injuries. Our continued studies have revealed that non-cytotoxic inhibition of neutrophil chemotaxis by SAP is paralleled by erythrocyte hemolysis by the same compound. Both neutrophil inhibitory and hemolytic activities appear to be a function of the peptide portion of SAP (determined by sensitivity to trypsin and pronase), which is augmented by the presence of sialic acid in the complex (activity eliminated by the addition of neuraminidase). The lipid portion of SAP, which is critical to its neutrophil immunosuppressive activity, does not appear to participate in erythrocyte hemolysis. Hemolytic activity of SAP is not due to protease activity, and does not appear to be receptor dependent. However, it is completely dependent upon the presence of calcium. The hemolytic activity of SAP appears to be abrogated by the addition of cerium nitrate, leading to a hypothesized relationship of SAP to the immunological activity of "burn toxin", previously described in detail (Schoenenberger, G.A. (1975) Monogr. Allergy 9, 72-139).