Immunologic alterations in a murine model of hemorrhagic shock

Objective: To study multiple immune parameters in mice subjected to severe hemorrhage without fluid resuscitation. Study Design: Controlled animal study. Anesthetized, female mice were hemorrhaged by tail bleeding. Immune parameters (spleen T-cell proliferation and activation, intracellular calcium flux, cytokine production, peritoneal neutrophil respiratory burst, and survival after intraabdominal septic challenge) were measured at 24, 48, and 72 hrs after hemorrhage. Measurements and Main Results: T-cell proliferation was decreased in animals after two 20% blood volume hemorrhages, 30 mins apart; single 30%, 40%, and 50% blood volume hemorrhages did not depress proliferation. 'Helper/inducer' T cells from twice-hemorrhaged mice showed decreased expression of activation antigens (interleukin-2 receptor, Ia) after mitogen stimulation. In contrast, 'suppressor/cytotoxic' T cells displayed increased activation, shown by augmented expression of interleukin- 2 receptor and Ia antigens. Leukocyte production of prostaglandin E₂, a mediator frequently implicated in immune down-regulation, was unaffected by hemorrhage. Secretion of tumor necrosis factor-α (TNF-α) in culture was increased when cells were harvested 48 hrs after injury. Intracellular calcium flux in stimulated lymphocytes was decreased 24 hrs after hemorrhage, suggesting deranged intracellular signal transduction. Respiratory burst activity of peritoneal neutrophils was unchanged following hemorrhage. When animals were subjected to septic challenge, the survival rate was markedly decreased after two hemorrhages (when sepsis was induced 24 hrs after hemorrhage). By 72 hrs posthemorrhage, most of the immunologic alterations, including resistance to septic challenge, had resolved. Conclusions: This uninstrumented hemorrhagic shock model allows quantification of multiple immune derangements. Immune suppression was identified after two smaller (20% blood volume) hemorrhages, but not after a single, larger hemorrhage. Immune derangements are maximal at 24 hrs posthemorrhage, and resolve in the subsequent 48 hrs.