Assessment of immunological status in the critically ill.

The systemic inflammatory response (SIRS) results from various types of injuries such as severe infection, trauma, ischemia-reperfusion and major surgery including cardiac surgery with cardio-pulmonary bypass. This response involves immune cell activation and a complex network of proinflammatory cytokines, which may induce multiple organ failure when uncontrolled. The monocyte plays a central role in the response to infection with the release of TNF, IL-1, and IL-12. In addition, monocytes present antigens to T lymphocytes. An optimal antigen presentation requires the expression of MHC class II HLA-DR on monocytes surface and of co-stimulatory molecules such as CD54 on monocytes and LFA-1 on lymphocytes. It has become increasingly apparent that the pro-inflammatory response is balanced by concomitant anti-inflammatory mechanisms that results in monocyte deactivation, characterized by a decrease in HLA-DR expression and the release of anti-inflammatory cytokines such as IL-10. This counterregulatory response, if prolonged or predominant, may predispose the patient to a higher risk of infection. Further studies need to be conducted to precise: 1) the intensity of depression of the surface molecule expression assessing monocyte function, such as HLA DR and CD54; 2) the level of IL-10 and IL-12 release in patients with severe sepsis; 3) the immunomodulating effects of frequently used treatments in these patients with severe sepsis and in surgical patients; 4) the time course of recovery; 5) if the monitoring of HLA-DR, CD54, IL-10 and IL-12 will better predict the clinical outcome than clinical parameters.