Abstract
Following surgical or accidental trauma many patients show suppression of cellular immunity. In this investigation sera from severely burned patients and patients undergoing aortic aneurysm repair were studied. Sera shown to suppress phytohaemagglutinin-induced blastogenesis of normal human lymphocytes were fractionated using ion exchange and G25 Sephadex chromatography. Suppressive activity was largely confined to a low molecular weight (LMW) fraction and was dose dependent. LMW fractions of normal sera had no significant suppressive activity. The purpose of this study was to test the causal relationship between immunosuppressive serum and decreased resistance to bacterial infection. Listeria monocytogenes infected mice were used as an in vivo model to test suppression of cellular immunity. Injection of LMW fractions of suppressive sera significantly increased mortality in these mice, but had no effect on non-infected mice. There was good correlation between the in vitro and in vivo effects of the suppressive fractions. These results suggest that a circulating factor in the serum of injured patients suppresses cellular immunity and may be responsible for impaired resistance to infection.