Mucosal damage and neutropenia are required for Candida albicans dissemination

Abstract

Candida albicans fungemia in cancer patients is thought to develop from initial gastrointestinal (GI) colonization with subsequent translocation into the bloodstream after administration of chemotherapy. It is unclear what components of the innate immune system are necessary for preventing C. albicans dissemination from the GI tract, but we have hypothesized that both neutropenia and GI mucosal damage are critical for allowing widespread invasive C. albicans disease. We investigated these parameters in a mouse model of C. albicans GI colonization that led to systemic spread after administration of immunosuppression and mucosal damage. After depleting resident GI intestinal flora with antibiotic treatment and achieving stable GI colonization levels of C. albicans, it was determined that systemic chemotherapy with cyclophosphamide led to 100% mortality, whereas selective neutrophil depletion, macrophage depletion, lymphopenia or GI mucosal disruption alone resulted in no mortality. Selective neutrophil depletion combined with GI mucosal disruption led to disseminated fungal infection and 100% mortality ensued. GI translocation and dissemination by C. albicans was also dependent on the organism's ability to transform from the yeast to the hyphal form. This mouse model of GI colonization and fungemia is useful for studying factors of innate host immunity needed to prevent invasive C. albicans disease as well as identifying virulence factors that are necessary for fungal GI colonization and dissemination. The model may also prove valuable for evaluating therapies to control C. albicans infections.

Figure 1. Gastrointestinal Colonization Levels of C3H/HeN Mice Fed C. albicans Strains SC5314 and CAF2–1

Mice were maintained on sterile water with 2 mg streptomycin/ml and 1,500 U penicillin G/ml throughout the duration of the experiment, and 0.2 mg gentamicin/ml was added once colonization was confirmed. Points represent results from individual animals, and horizontal lines represent the medians. n = 16 for each strain.

Figure 2. DSS-Induced Murine Gastrointestinal Mucosal Damage

Histological sections of cecums from mice colonized with C. albicans strain SC5314 with continuation of penicillin, streptomycin, and gentamicin in the drinking water then given water with 2.5% DSS for various periods with or without induction of neutropenia. (A) No DSS, 200 μg of RB6-8C5 IP once. (B) DSS for 3 d. (C) DSS for 7 d. (D) DSS for 7 d and after the third day of DSS mice were given 200 μg of RB6-8C5 IP once and observed for 96 h after the RB6-8C5 dose. Magnification: Objective 10×. Sections in (A) and (B) have normal histologic appearance, whereas in panels (C) and (D) disruption of the epithelial barrier integrity was clearly seen.

Figure 3. Viable Counts of C. albicans Strains SC5314 or CAF2–1 in the Livers of Deceased C3H/HeN Mice that Were Previously Colonized in the GI Tract with C. albicans and Subsequently Given Various Forms of Immunosuppression

Cy, cyclophosphamide; MTX, methotrexate; RB6, RB6-8C5 mAb; DSS, dextran sulfate sodium. Points represent results from individual animals. Horizontal lines with bars represent median with interquartile range when n > 3, otherwise only the median is shown.

Figure 4. Gastrointestinal Colonization Levels of Female 6- to 8-Wk-Old C3H/HeN Mice Fed C. albicans Strains CAF2–1, HLC-54 (Δefg1/cph1), and BCa-210 (Δtup1)

Points represent results from individual animals, and horizontal lines represent the medians. n = 8 for CAF2–1, n = 7 for Δefg1/cph1 and Δtup1. Colonization levels with strain Δtup1 were significantly lower (p = 0.0003 by Mann Whitney test) compared with other two strains.

Figure 5. Survival Curve of C3H/HeN Mice Fed C. albicans Strains CAF2–1, HLC-54 (Δefg1/cph1), or BCa-210 (Δtup1) and Subsequently Given mAb RB6-8C5 (200 μg IP) and Methotrexate (150 mg/kg/dose IP)

Median survival of mice colonized with strain Δefg1/cph1 was significantly higher than that of mice colonized with wild-type C. albicans CAF2–1 (p = 0.01, log rank test). Each group contained 8 mice.

Figure 6. Schema for Murine Model of C. albicans Gastrointestinal Colonization and Dissemination after Administration of Immunosuppression