Characteristics of Invasive Candidiasis in Gamma Interferon- and Interleukin-4-Deficient Mice: Role of Macrophages in Host Defense against Candida albicans

Murine models of invasive candidiasis were used to study the in vivo importance of gamma interferon (IFN-γ) and interleukin-4 (IL-4) in host defense against Candida albicans and to characterize the tissue inflammatory reactions, with special reference to macrophages (Mφ). Knockout (KO) IFN-γ-deficient (GKO) and IL-4-deficient (IL-4 KO) and C57BL/6 parental mouse strains were challenged intraperitoneally with 10⁸ C. albicans blastoconidia. Survival of GKO mice was significantly lower (16.7%) than that of C57BL/6 control (55.5%) and IL-4 KO (61.1%) animals, but was not correlated with the extent of organ colonization. Immunohistological analysis with a panel of myeloid and lymphoid markers revealed multiple renal abscesses, myocarditis, hepatitis, meningoencephalitis, and pneumonia in each strain, with a dominant presence of Mφ. In the absence of IFN-γ, C. albicans induced striking changes in the phenotype of alveolar Mφ and extensive perivascular lymphoid infiltrates in the lung. Impairment in nitric oxide production by peritoneal Mφ was shown only in GKO mice, and they produced Candida-specific immunoglobulin G (IgG), IgM, IgA, and IgG subclasses in lower titers. Our in vivo studies with KO mice elucidate a critical role for IFN-γ, but not IL-4, in host defense against C. albicans.Candida albicans is a common commensal organism in humans, and its importance as an opportunistic pathogen, particularly in immunocompromised patients, has continued to increase over the last two decades. According to the National Nosocomial Infections Surveillance System, the ratio of C. albicans isolates among nosocomial fungal infections increased from 52% to 63% in the 1980s (4). Phagocytic cell defects generally predispose to disseminated candidiasis; candidemia was calculated to result in 38% excess mortality and extend hospitalization by approximately 30 days (40). Besides the efforts to develop more effective and safer antifungal agents, a new therapeutic approach to augment the antifungal capacity of the host’s immune system should be investigated.The mechanisms of host defense and pathogenesis of candidiasis are not completely understood. Optimal phagocytosis of C. albicans requires opsonization; however, unopsonized yeast can be internalized by macrophages (Mφ) through the mannose receptor (21). Efficient killing of C. albicans by mononuclear phagocytes requires respiratory burst-associated toxic compounds (22), and recent data suggest that nitric oxide (NO) may also be involved in anticandidal functions of Mφ (5). Experimental evidence suggests that mononuclear phagocytes could play an important role in eradication of this pathogen, and their anticandidal activity can be augmented in vitro with granulocyte-Mφ and Mφ colony-stimulating factors and cytokines (no significant change could be measured in the level of specific immunoglobulin A [IgA] in serum or among the levels of interleukin-3 [IL-3] and gamma interferon [IFN-γ]) in both human and murine systems (23, 25, 28, 39).The in vivo benefit of cytokine treatment in disseminated candidiasis has not been established, and data from different murine models are controversial. Administration of IFN-γ has been reported to be associated with improved survival of mice after lethal challenge with C. albicans, which correlated with the anticandidal activity of peritoneal Mφ (28); another study showed a reduction in tissue fungal burden in IFN-γ-treated mice (19). However, in a different murine model, in vivo administration of IFN-γ resulted in increased susceptibility and organ colonization of four infected inbred strains (13). In vivo administration of IL-12, which has been reported to prime naive T cells for high IFN-γ expression and skew cytokine production toward a Th1-type response (38), did not modify the course of systemic candidiasis (32). In contrast, Th2-type cytokines IL-4 and IL-10 have been reported to exacerbate infection, and neutralization of IL-4 by specific antibody or soluble IL-4 receptor resulted in an enhanced production of Th1 cytokines, associated with increased resistance to systemic murine candidiasis (26, 30, 37). The controversial results of in vivo cytokine treatment may be the consequence of genetic differences among the infected strains and also the variation in protocols; the kinetics of cytokine production are influenced by several host and pathogen factors, and the effect of exogenous cytokine might depend on the condition of the infected host and stage of infection.Cytokine and receptor gene disruption strategies make it possible to examine the role of cytokines in host response to different pathogens directly. Recent studies showed an increased susceptibility of IFN-γ–receptor knockout (KO) mice to Mycobacterium bovis or Mycobacterium tuberculosis, but not to Schistosoma mansoni (1, 7, 8). Another study reported that disruption of the IFN-γ receptor gene was associated with higher susceptibility to Leishmania major and that IL-4 deficiency resulted in increased resistance, but only in certain inbred strains (17).Our study was undertaken to investigate the in vivo role of IFN-γ and IL-4 in disseminated C. albicans infection and characterize the tissue inflammatory cells by immunohistochemistry and by functional assays ex vivo. We demonstrate that IFN-γ, but not IL-4, is essential for survival in invasive candidiasis and show the dominant participation of Mφ in the inflammatory lesions of different tissues in KO as well as wild-type mice. In the absence of IFN-γ, a striking local immune regulatory alteration was observed in the lungs.