Cellular and humoral bases of hemorrhage-induced depression of lymphocyte function

Bacterial infection often occurs after trauma and hemorrhage and is believed to be a reflection of a compromised host defense system. In the present study, the effect of hemorrhage on phytohemagglutinin-induced lymphocyte proliferation was investigated. Lymphocytes obtained from rats 2 h after blood withdrawal in an amount equivalent to 30% of total blood volume showed a 48% reduction in proliferative response as compared to cells obtained from the same animal before bleeding. This depression in lymphocyte proliferative capacity appeared to be due to a serum factor or factors induced by hemorrhage. The hemorrhage-induced serum factor(s) is heat-stable, dialyzable, and has an apparent molecular weight between 13,000 and 23,000 on gel filtration chromatography. The hemorrhage-induced factor seems to suppress lymphocyte proliferation in a rapid and irreversible manner. This abnormality in host defense mechanisms may contribute to the increased incidence of sepsis present after trauma and hemorrhage.