Suppression of in vitro lymphocyte and neutrophil responses by a low molecular weight suppressor active peptide from burn-patient sera.

Thermal injury produces profound pathophysiological changes in the severely burned patient. Primary among these is the modulation of immunity, leading to episodes of immunosuppression and thus increasing the risk of sepsis and possible death. We herein report the isolation of a low molecular weight suppressor active peptide (SAP) which appears to be responsible for many of the observed immunologic changes in burned patients. SAP suppressed T-lymphocyte blastogenesis in the mixed lymphocyte reaction (MLR) and inhibited neutrophil chemotaxis (CTX) in vitro. Characterization of SAP revealed a complex structure comprised of (1) a peptide component rich in glycine, serine, and alanine; (2) a carbohydrate component containing sialic acid; and (3) a fatty acid component, tentatively identified as prostaglandin E. The immunosuppressive activity of SAP is dependent upon the presence of all three structural components. The molecular weight of SAP was estimated to be 3654 as determined by Amicon cell ultrafiltration and amino acid analysis. The isoelectric point of SAP was estimated by chromatofocusing and ion-exchange chromatography to be between 3.2 and 3.6. We hypothesize that the suppressor active peptide may be comprised of cellular or tissue components released into the circulation at the time of injury.