A reactive monocyte subset characterized by low expression of CD91 is expanded during sterile and septic inflammation.

This study was undertaken to assess CD91 expression on monocytes and changes in monocyte subset distribution during acute tissue damage and bloodstream infection (BSI). We investigated blood specimens from healthy individuals, trauma and cardiac surgery patients as a model of tissue damage, and patients with BSI, by flow cytometry using a panel of antibodies comprising CD45, HLA-DR, CD14, CD16 and CD91 for the identification of monocyte subsets. While infrequent in healthy subjects, CD91low/neg monocyte levels were markedly high in BSI, trauma and after cardiac surgery. This monocyte subset expanded up to 15-fold in both patient cohorts, whereas CD14+CD16+ inflammatory monocytes were multiplied by a factor of 5 only. CD14+CD91low monocytes displayed a significantly lower density of HLA-DR and markedly reduced expression of CD300e, compared to the other subsets. They also expressed high levels of myeloperoxidase and showed robust phagocytic and oxidative burst activity. Expansion of CD91low monocytes is a sensitive marker of acute inflammatory states of infectious and non-infectious etiology. [ABSTRACT FROM AUTHOR]