During bacterial related sepsis, one of the key playing cells are macrophages, monocytes and T-lymphocytes (Hotchkiss et al., 2003). Macrophages and monocytes are supposed to be essential for the septic reaction to Gram-negative bacteria (Hotchkiss et al. 2003). Generally, there are two dominant types of macrophages: the pro-inflammatory M1 macrophage and the anti-inflammatory M2 macrophage (Mantovani et al., 2006). Similar to this macrophage characteristics, monocytes can also be categorized into pro-or anti-inflammatory. These macrophage/monocyte phenotypes can be differentiated in vitro from freshly isolated human blood monocytes using either GM-CSF giving raise to M1 macrophage/monocyte or M-CSF resulting in M2 macrophage/monocyte (Mantovani et al., 2006; Neu et al., 2013). Brunialti et al. (2012) have already demonstrated that the population of antiinflammatory M2 monocytes in septic patients is bigger than the pro-inflammatory M1 population. However, the authors did not further analyze the underlying mechanisms of M2 polarization nor did they identify the sepsis-causing pathogens.
In the present study, monocytes and macrophages of patients with Pseudomonas aeruginosa (PSA) sepsis are characterized by their surface marker expression profile via flow cytometry and cytokine pattern by ELISA in vivo and after ex-vivo LPS stimulation. In addition, an ex-vivo model system for PSA induced sepsis is validated. Blood of critically ill patients in the ICU infected with PSA is sampled to isolate peripheral blood mononuclear cells (PBMCs). Blood monocytes are analyzed for surface marker expression to determine the relative proportions of M1 and M2 monocytes in these patients and in healthy controls by flow cytometry
