Association of sepsis with an immunosuppressive polypeptide in the serum of burn patients.

One hundred ninety serum samples from 51 burned patients were tested for immunosuppressive activity which might explain decreased host immune competence following thermal injury. The serum from a variable but significant percentage of these patients suppressed the response of normal human peripheral blood lymphocytes to phytohemagglutinin. The occurrence of immunosuppressive activity paralleled the severity of the injury. Ten of ten severely burned patients (severity index greater than 40), but only 20 of 30 patients with index 10--39.9, and three of 11 patients with Index 0--9.9 developed suppressive serum. Differences between these groups were significant (p less than .05). In all 19 patients who became septic, immunosuppressive serum activity immediately preceded or coincided with the septic episode. In contrast to the effect on lymphocytes, burn sera stimulated fibroblast proliferation. Immunosuppressive activity did not correlate with serum cortisol levels, blood transfusion, protein-calorie malnutrition, or anesthesia. Suppressive sera were not cytotoxic. A majority of the active serum factor(s) was contained in a low molecular weight (less than 10,000 daltons) polypeptide subfraction.