Background: Sepsis is a serious disease with a high case fatality rate. A variety of changes in the host immune responsiveness are observed in the pathogenesis of sepsis, ranging from detrimental hyperinflammation to profound immunoparalysis, i.e. acquired immunodeficiency. The level of monocyte HLA-DR expression reflects the functional status of monocytes as antigen-presenting cells and granulocyte CD64 expression is also indicative of infectious inflammation. Material and Methods: Monocyte HLA-DR expression and granulocyte CD64 expression were measured in 49 septic patients and 30 healthy controls using flow cytometry focused on three parameters: positive cell percentage, mean fluorescence intensity and quantitation of antibodies bound per cell (QuantiBRITE). Results: The significance of both monocyte HLA-DR expression and granulocyte CD64 expression in septic patients was confirmed. Monocyte HLA-DR dramatically decreases in septic patients compared to controls, is one of the prognostic factors and correlates with C-reactive protein. In contrast, granulocyte CD64 sharply rises in patients with sepsis and correlates with mediators of systemic inflammation (procalcitonin – PCT), proinflammatory mediators (interleukin-6 – IL-6, lipopolysaccharide binding protein – LBP) and anti-inflammatory cytokines (interleukin-10 – IL- 10). Conclusion: Quantitative monocyte HLA-DR expression and granulocyte CD64 expression are useful indicators in septic patients when considered along with the panel of other markers, monitored over a period of time and in the context of the clinical course of sepsis.

        Key words: sepsis – immunoparalysis – HLA-DR – CD64 – QuantiBRITE.