Injury induces deficient interleukin-12 production, but interleukin-12 therapy after injury restores resistance to infection

Objective To assess at serial intervals the production of interleukin-12 (IL-12) by m onocytes/macrophages from the peripheral blood of injured patients and cont rol subjects, and using a mouse model to confirm human findings and explore the effectiveness of low-dose IL-12 therapy in restoring resistance to inf ection after injury. Summary Background Data Serious injury is associated with loss of function of the T helper 1 lympho cyte phenotype, but little is known about IL-12 production in injured patie nts. The authors previously reported that early, moderate-dose IL-12 therap y in a mouse model of burn injury restored resistance to a later infectious challenge (cecal ligation and puncture, CLP). However, the efficacy of cli nically relevant low-dose IL-12 therapy carried out to or beyond the time o f septic challenge remains to be tested. Methods Peripheral blood mononuclear cells (PBMCs) and adherent cells were obtained from 27 patients with major burns or traumatic injury and 18 healthy perso ns and were studied at serial intervals for IL-12 production stimulated by bacterial lipopolysaccharide (LPS). PBMCs from 18 of the same patients were studied for IL-10 production as well. IL-12 production by adherent cells f rom the spleens of burn or sham burn mice was studied at serial intervals a fter injury to confirm the human findings. Low-dose IL-12 or vehicle was gi ven every other day to groups of burn and sham burn mice, which were then c hallenged with CLP on day 10, and survival was determined. Finally, spleens were harvested from burn or sham burn animals receiving low-dose IL-12 or vehicle after CLP. After splenic cellularity was determined by hemocytomete r, splenocytes were cultured and production of tumor necrosis factor-alpha, interferon-gamma, and IL-10 were assessed by immunoassay. Results Adherent cells from patients' PBMCs produced significantly less IL-12 than normal PBMCs after injury, reaching a nadir 8 to 14 days after injury. Stim ulation of whole PBMCs by LPS indicated that at 8 to 14 days after injury, IL-12 production by PBMCs was significantly lower and IL-10 production was significantly higher than that of PBMCs from healthy persons. Low-dose IL-1 2 therapy significantly increased survival after CLP. Splenocytes from burn mice treated with IL-12 had significantly increased production of TNF-alph a and IF-gamma, both before and after CLP, when compared with vehicle-treat ed burn animals. IL-10 production by burn splenocytes remained high after I L-12 treatment. Splenic cellularity increased after IL-12 treatment in burn mice. Conclusion The capacity to produce IL-12 by adherent cells of the monocyle/macrophage lineage is significantly reduced after serious injury in humans and in a mo use burn model. In humans, there is a reciprocal relation between diminishe d IL-12 production and increased IL-10 production at approximately 1 week a fter injury. Low-dose IL-12 therapy in the mouse burn model markedly increa sed survival after a septic challenge, even when treatment was carried beyo nd the onset of sepsis. Low-dose IL-12 treatment in the mouse increased pro duction of proinflammatory mediators important in host defense and at the s ame time maintained or increased production of IL-10, an important antiinfl ammatory cytokine.