Immunological and pathological observations withCandida albicans-infected animals

[Electron microscopy of Candida albicans]

The multiplicity of information which electronmicroscopy has contributed to our knowledge of Candida albicans and its relationship to the human host is reviewed and by means of examples presented.

Influence of muramyl dipeptide on renal candidiasis in genetically distinct mice

Susceptible (DBA/2) and resistant (C57BL/6) mice were inoculated intravenously with Candida albicans to evaluate the effect of a four-day prophylaxis with muramyl dipeptide (MDP) on the renal burden of organisms during the first week after infection. In sham-treated DBA/2 mice injected with 8 x 10(4) candida cells, renal CFU (LOG10 +/- SEM) on days 1, 4 and 7 after infection were found to average 5.050 +/- 0.109, 4.882 +/- 0.133 and 5.482 +/- 0.245. In sham-treated C57BL/6 mice injected with 2 x 10(5) candida cells, renal CFU on days 1, 4 and 7 reached only 3.610 +/- 0.118, 3.404 +/- 0.107 and 4.176 +/- 0.580. MDP-treated DBA/2 mice achieved significant reduction in CFU of C. albicans on day 1 (1.3 log units) and day 4 (0.6 log unit), while MDP-treated C57BL/6 mice had significant reduction in CFU of C. albicans only on day 1 (0.6 log unit) after infection. Sham-treated mice of both strains had a 28.6 to 30% increase in kidney weights on day 4 only, a transient change not seen in MDP-treated mice. Histopathological examination on days 8, 15 and 21 after infection revealed a higher incidence of renal papillary necrosis in DBA/2 mice than C57BL/6 mice (approximately 70% vs 10%). The incidence of granulomas and of chronic interstitial inflammation was much higher in MDP-treated mice. We conclude that the genetic makeup of the host influences the potential effectiveness of MDP as a biological response modifier.

Studies of the role of B-cells in the resistance of mice to experimental candidiasis

The role of humoral immunity in experimental candidiasis was studied in B-cell-deficient mice. The B-cell deficiency was produced by administration of anti-mu antibodies to newborn animals. These anti-IgM-treated mice failed to produce antibodies against sheep red blood cells (SRBC), and their lymph nodes and spleens did not form germinal centres. However, their cell-mediated immune responses were normal as they developed delayed hypersensitivity to SRBC and rejected skin allografts like normal animals. These B-cell-deficient animals along with the controls were infected with one LD50 dose of Candida albicans. These animals were observed for mortality, antibody formation, delayed type hypersensitivity (DTH) to Candida antigen and viable count of the organism in different organs. The course of the experimental infection was almost parallel in both the groups. B-cell deficiency did not increase the susceptibility of the animals to experimental candidiasis.

Studies of experimental candidiasis in T-cell-deficient mice

The role of cell-mediated immunity (CMI) in the protection against experimental murine candidiasis was studied. CMI-deficient animals prepared by adult thymectomy and treatment with antimouse thymocyte serum along with controls were challenged with one LD50 (6.6 X 10(4)) dose of Candida albicans. The course of infection in these animals was studied by mortality pattern, delayed type hypersensitivity reaction (DTH) to candida antigen, antibody formation, and viable count of organisms in kidney, spleen and liver at different time intervals. The T-cell-deficient animals were found to be highly susceptible to infection with C. albicans. A correlation was observed in the appearance of DTH and protection.

Vaccines against fungal infections

The state-of-the-art reached in developing protective immunity against fungal infections through vaccination makes a survey of methodologies and results timely. This review describes experimental vaccinations against dermatophytes, pathogenic yeasts, and dimorphic fungi with special attention to the anti-Coccidioides immitis vaccine, which has reached clinical trials, and to the anti-Candida albicans and anti-Histoplasma capsulatum ribosomal vaccines. Also covered are vaccination experiments in compromised hosts aimed at eliciting acquired resistance to opportunistic fungal infections which constitute risk factors for these hosts. Immunization procedures include live, killed, and attenuated organisms, as well as different subcellular fractions such as cytoplasmic extracts, fungal culture filtrates, cell walls, or ribosomal fractions. A variety of experimental animal models and isolated human trials constitute the subjects in these studies. Acquired immunity has been evaluated through assessment of resistance to infection and determination of specific immune responses. It has been demonstrated that fungal vaccines do elicit both humoral and cell-mediated immunity in the immunized host. For some vaccines (e.g., H. capsulatum), a correlation between the induced immunity and protection was observed and the immunity could be adoptively transferred. In view of the potential of vaccines against fungal infections, a perspective on their applicability, significance, and value for human use is discussed.