Immunomodulatory therapies in sepsis

Abstract

Despite advances in critical care medicine, mortality from sepsis in ICU patients remains high. In response to several infectious and non-infectious stimuli, monocytes/ macrophages release a number of mediators, including cytokines, involved in the proinflammatory response that underlies sepsis. The excessive release of these mediators results in the development of whole body inflammation, and plays an important role in the pathogenesis of sepsis and septic shock. In addition, patients with sepsis also undergo an anti-inflammatory phase (the compensatory anti-inflammatory response syndrome) and at times, a mixed response with both pro-and anti-inflammatory components (the mixed antagonistic response syndrome). The initial systemic hyperinflammation is caused by production of inflammatory cytokines, especially tumour necrosis factor-a (TNF-alpha), and also interleukin-1 (IL-1), IL-6, and interferon gamma, which act synergistically with TNF-alpha in inducing shock in animal models. However, clinical trials aimed at downregulating these mediators using antibodies against endotoxin, TNF-alpha, antagonists of IL-1 or platelet activating factor have proved to be uniformly disappointing. Not only have these agents been found to have no effect, but they may also increase mortality. One of the reasons for such failure may be the lack of precise immunological monitoring during the course of sepsis. We have recently demonstrated that sepsis shows a biphasic immunological pattern during the initial and later phase: the early hyperinflammatory phase is counterbalanced by an anti-inflammatory response which may lead to a hypoinflammatory state. The latter is associated with immunodeficiency that is characterised by monocytic deactivation, so-called immunoparalysis. Interferon gamma-1 b has an immunoregulatory effect in patients with immunoparalysis during the compensatory anti-inflammatory response syndrome, not only restoring levels of HLA-DR expression but also reestablishing the ability of monocytes to secrete cytokines such as TNF-alpha. By monitoring immune status in septic patients, targeted intervention may lead to more success in immunomodulation of sepsis.