Exacerbation of invasive Candida albicans infection by commensal bacteria or a glycolipid through IFN-γ produced in part by iNKT cells.

BACKGROUND The commensal yeast Candida albicans is a major cause of invasive fungal infections. Despite treatment with antifungal agents, the mortality rate attributed to these types of infection is high. Although numerous cases have been reported regarding a poor outcome for patients with bacterial and C. albicans coinfection, the mechanisms by which the coinfecting bacteria exacerbate the C. albicans infection remain elusive. METHODS AND RESULTS We evaluated how glycolipid-mediated activation of invariant natural killer T (iNKT) cells affects the clearance of C. albicans. Surprisingly, C. albicans-infected, glycolipid-treated mice exhibited significantly lower survival rates, increased fungal burden, and higher interleukin (IL)-6 production in the kidneys compared with control mice. Glycolipid-induced exacerbation of C. albicans infection was not observed in interferon-gamma knockout (IFN-γKO) mice. In the C. albicans-infected, glycolipid-treated mice, the number of neutrophils in the blood and bone marrow dramatically decreased in an IFN-γ-dependent manner. Furthermore, mice that were coinfected with C. albicans and nonfermentative gram-negative commensal bacteria exhibited increased fungal burden and inflammatory cytokine production in the kidneys that were dependent on IFN-γ and iNKT cells. CONCLUSIONS Our results indicate that coinfecting commensal bacteria exacerbate C. albicans infection through IFN-γ produced, in part, by iNKT cells.