Immunosuppression after Endotoxin Shock: The Result of Multiple Anti-inflammatory Factors

OBJECTIVES Endotoxin induced suppression of cellular immune function is thought to contribute to septic complications in trauma patients. A rabbit model of endotoxemia was used to determine the relative roles of the anti-inflammatory factors interleukin-4 (IL-4), interleukin-10 (IL-10), transforming growth factor beta1 (TGFbeta1), and prostaglandin E sub 2 (PGE2) in addition to other factors, in inducing immunosuppression. DESIGN T-cell suppressive factors (TSF) in serum ultrafiltrates were separated and tested for the presence of the known suppressive factors PGE sub 2, IL-4, IL-10, and TGFbeta1. MATERIAL AND METHODS New Zealand rabbits were injected with 50 microg/kg of purified Escherichia coli lipopolysaccharide. Animals were exsanguinated after 48 hours and serum was separated by ultrafiltration (cutoff 50 kd), TSK HW-40 size exclusion chromatography, and Q-Sepharose anion exchange chromatography. TSF activities of chromatographic fractions and serum samples were measured with a miltogen induced in vitro T-cell proliferation assay. Levels of PGE2, IL-4, IL-10, and TGFbeta1 were measured with enzyme immunoassays. MEASUREMENTS AND MAIN RESULTS Serum TSF activity, and levels of PGE sub 2, IL-4, IL-10, and TGFbeta1 were increased after endotoxemia. Size exclusion chromatography revealed three major fractions (TSF1 sub -3) with up to 600 times more TSF activity compared with controls. IL-4 and IL-10 were found in TSF1 and TSF3. Further separation of TSF1 by anion exchange chromatography revealed a total of eight different T-cell suppressive factors. TGFbeta1 probably remained in the retentate after ultrafiltration, while PGE2 eluted at a higher retention time. The known anti-inflammatory factors TGFbeta1, IL-10, IL-4, and PGE2 only accounted for 13% of the total serum TSF activity of 614 U/mL. CONCLUSIONS Lipopolysacchoride shock results in the release of multiple T-cell suppressive factors in addition to known immunosuppressive factors, all of which contribute to the antiinflammatory response.