Viridans streptococcal septicaemia in neutropenic patients: role of proinflammatory cytokines

The immunostimulatory activity of viridans streptococcal strains isolated from neutropenic patients with severe sepsis (n=9) or uncomplicated bacteraemia (n=10) was compared. Peripheral blood mononuclear cells from healthy individuals were stimulated with heat-killed bacteria or culture supernatants, and cytokine production assessed. All strains were potent inducers of IL1β, IL8, and TNFα production. Heat-killed bacteria induced consistently higher IL1β and TNFα production than did the cell-free bacterial supernatants (P<0.01). The strains did not induce any proliferative response, nor any significant TNFβ or IFNγ production. No difference in cytokine-inducing capacity could be detected between the cohorts of severe and nonsevere isolates. Comparison of strains causing severe and nonsevere episodes in the same patient (n=2) revealed a significantly higher induction of IL1β by the severe episodes associated isolates as compared to the nonsevere (P<0.04). The study underscores the importance of the host–pathogen interplay in determining the level of inflammation, and hence the severity of disease.