MAJOR INJURY LEADS TO PREDOMINANCE OF THE T-HELPER-2 LYMPHOCYTE PHENOTYPE AND DIMINISHED INTERLEUKIN-12 PRODUCTION ASSOCIATED WITH DECREASED RESISTANCE TO INFECTION

Objective Patients with serious traumatic injury and major burns and a n animal model of burn injury were studied to determine the effect of injury on the production of cytokines typical of the T helper-2 lympho cyte phenotype as opposed to the T helper-1 phenotype and on the produ ction of interleukin-12. Summary Background Data Perturbations of natu ral and adoptive immunity are related to the increased susceptibility to infection manifested by seriously injured and burn patients. Earlie r work has shown that impaired adoptive immunity after injury is chara cterized by diminished production of interleukin-2 (IL-2), a product o f Th lymphocytes. Exposure of naive Th cells to certain antigens and c ytokines causes conversion to either the Th-1 or the Th-2 phenotype. T h-1 cells produce IL-2 and interferon-gamma (IFN-tau) and initiate cel lular immunity. Th-2 cells secrete interleukin-4 (IL-4) and interleuki n-10 (IL-10) and stimulate production of certain antibodies. Conversio n to the Th-1 phenotype is facilitated by IL-12, and conversion to the Th-2 phenotype is promoted by IL-4. The authors believed that serious injury might cause conversion of Th cells to the Th-2 as opposed to t he Th-1 phenotype rather than generalized Th suppression. Methods The authors studied circulating peripheral blood mononuclear cells (PBMC) from 16 major burn and 8 trauma patients on 32 occasions early after i njury and from 13 age- and sex-matched healthy individuals for cytokin e production after phytohemagglutinin stimulation. Also studied was a mouse model of 20% burn injury known to mimic the immune abnormalities seen in humans with burns. Splenocytes from burn mice, 10 to 12 per g roup, were studied after activation by concanavalin A or by the bacter ial antigen Staphylococcus aureus Cowan strain I for cytokine producti on and cytokine messenger RNA expression as determined by reverse tran scriptase polymerase chain reaction. Burn mice were compared with sham -bum controls and attention was focused on day 10 after burn injury, a time when IL-2 production and resistance to infection are highly supp ressed. Finally, burn and sham-burn animals, 20 per group, were treate d in vivo with IL-12 (25 ng daily for 5 days) and observed for mortali ty after septic challenge (cecal ligation and puncture [CLP]) performe d on day 10 after injury. Results Peripheral blood mononuclear cells f rom burn and trauma patients produced less IFN-tau, the index cytokine of Th-1 cells, than PBMCs from healthy individuals 1 to 14 days after burn injury (SE = 77.6 +/- 16 pg/mL patients vs. 141.3 +/- 35 pg/mL c ontrols, p < 0.05). However, production of IL-4, the index cytokine of Th-2 cells, by patient PBMCs was increased (51.0 +/- 13.0 pg/mL patie nts vs. 26.9 +/- 2.5 controls, p < 0.05). Splenocytes from mice 10 day s after burn injury, when compared with sham-burn controls, showed dim inished production of IL-2 (1.04 +/- 0.91 units/mL burns vs. 5.8 +/- 0 .55 units/mL controls, p < 0.05) and IFN-tau (1.05 +/- 0.7 units/mL bu rns vs. 12.0 +/- 8.9 units/mL mL controls, p < 0.05). However, burn sp lenocytes produced more IL-4 (2492 +/- 157.0 pg/mL burns vs. 672.0 +/- 22.7 pg/mL controls, p < 0.01) and IL-10 (695.2 +/- 20.8 pg/mL burns vs. 567.0 +/- 16.7 pg/mL controls, p < 0.05). Splenocyte production of IL-12 was also reduced after burn (0.20 +/- 0.035 units/mL) as compar ed with sham burn (0.46 +/- 0.08 units/mL, p < 0.05). The reduction in IL-2, IFN-tau, and IL-12 production by burn splenocytes was reflected by a tenfold decrease in expression of their respective cytokine mRNA s. In vivo IL-12 treatment of burn animals decreased mortality from CL P on day 10 after injury from 85% to 15% (sham-burn mortality after CL P, 15%, p < 0.05) and increased splenocyte IFN-tau production to supra normal levels. Conclusions Serious injury induced diminished productio n of IL-12 and a shift to the Th-2 phenotype with increased production of IL-4 and IL-10, cytokines known to inhibit Th-1 function. The abil ity of exogenous IL-12 to restore Th-1 cytokine production and resista nce to infection suggests a therapeutic role for IL-12 in the immune d ysfunction seen after major injury.