Immunity to Candida albicans induced by Listeria monocytogenes

In vitro study of contact-mediated killing of Candida albicans hyphae by activated murine peritoneal macrophages in a serum-free medium

Activated peritoneal macrophages obtained from Listeria-immune mice were demonstrated to kill nonphagocytosable Candida albicans hyphae by contact-mediated mechanisms in a serum-free synthetic medium. The actual killing of hyphae was confirmed by a microculture technique utilizing the dimorphic nature of the fungus. The most efficient candidacidal activity was demonstrated by the macrophages obtained from mice first immunized with live Listeria monocytogenes and then elicited with heat-killed L. monocytogenes cells. Resident macrophages from control mice showed only low candidacidal activity against C. albicans hyphae and yeast cells. Direct physical contact appeared to be required for macrophages to efficiently kill oversized C. albicans hyphae. Efficient in vitro killing of hyphae also required relatively high effector/target cell ratios (50 or higher). The contact-mediated candidacidal activity of activated macrophages was not significantly abrogated by oxygen-radical scavengers, suggesting the involvement of oxygen-independent mechanisms. These results suggest that the enhanced nonspecific immunity to candidiasis seen in Listeria-immune hosts can be attributed, at least in part, to activated fungicidal macrophages. The ability of macrophages to detect and destroy both yeast and hyphal C. albicans cells is clearly an important element of the host defense against candidiasis.

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.

Mouse candidiasis. II. Host responses are T-cell dependent and regulated by genes in the major histocompatibility complex

Administration of a Thy-1.2-specific monoclonal antibody to BALB/c mice resulted in a significant decrease in the efficiency of clearance of Candida albicans from the spleen. The rate of clearance of organisms from the spleen of congenic mice was determined by genes in the major histocompatibility complex, as was the magnitude of the inflammatory response in the popliteal lymph node after footpad immunization. These results formally demonstrate the involvement of T cells in host responses to primary candida infection.

Pathological observations in experimental candida infection of sensitized guinea pigs

Guinea pigs immunized intramuscularly with heat-killed or viable Candida albicans were infected intracutaneously with C. albicans. Animals with negative delayed hypersensitivity against C. albicans antigen showed similar lesions with non-immunized controls. Delayed hypersensitivity-positive guinea pigs, which were detected in the animals immunized with heat-killed C. albicans in CFA and IFA, demonstrated a delay of the resolution of the inflammatory tissue reaction and, in the animals immunized with C. albicans in CFA, developed a granuloma. These results suggest that both humoral and cell-mediated immunities do not play a significant role for protection against candidiasis and at a late stage of infection, cell-mediated immunity may play a secondary role of the enhancement of resistance to candida infection associated with granuloma formation.

Role of antibodies and effect of BCG vaccination in experimental candidiasis in mice

The role of humoral antibodies and the effect of BCG vaccination were studied in the experimental candidiasis in mice. The antibody suppressed, B-cell deficient animals were prepared by repeated administration of rabbit anti-mouse-mu-antiserum to the new born mice from birth onwards. Such immunodeficient animals along with controls were infected intravenously with Candida albicans, to study the course of candidal infection. It was observed that B-cell-deficient animals were found to be more susceptible to candidal infection than the controls, as indicated by their steady loss of body weight, longer mean time to death and higher viable counts of candidal cells in different organs. The anti-candidal antibodies were absent in all B-cell-deficient animals but present in the controls. These results suggest that antibodies make a contribution in protection against candidal infection in mice. The BCG vaccinated animals were prepared by repeated intravenous administration of BCG to mice and these vaccinated animals along with unvaccinated controls were challenged intravenously with C. albicans, to study the course of candidal infection. It was observed that BCG vaccination prolonged meantime to death and reduced the number of candidal cells in their kidneys.

Studies on defense mechanisms against Candida albicans infection in congenitally athymic nude (nu/nu) mice

The defense mechanisms against Candida albicans infection were studied by using a mouse thigh lesion model in congenitally athymic nude (nu/nu) mice and their normal littermates (nu/+). Nu/nu mice were more resistant to C. albicans infection than nu/+ mice judging from the course of the thigh lesion, the results of CFUs (colony-forming units) of C. albicans in the lesion, and histopathological observations. Histopathological and serological studies revealed that granulocytic cellular infiltration was predominant, and there were few indications of development of cell-mediated immunity to protect Candida infection in Candida-infected nu/nu and nu/+ mice. These results confirmed that lower susceptibility of nu/nu mice to C. albicans infection as compared to nu/+ mice was due to accelerated non-specific defense mechanisms in nu/nu mice, and that cell-mediated or humoral immunity played a minor role in the defense against Candida infection in this experimental model. Furthermore, treatment with high titer of rabbit anti-C. albicans serum was effective to control the number of Candida cells in thigh lesions of BALB/c mice. Above experimental results seem to clearly indicate the great variability of defense manifestation according to the experimental model exployed.

Immune responses to Candida albicans in genetically distinct mice

Mice from six genetically distinct strains were examined for their immune responses to Candida albicans in in vitro and in vivo assays, and naive mice and mice immunized with the fungus were challenged intravenously with three different doses of C. albicans to determine differences in susceptibility. Naive mice from the six groups showed substantial differences in resistance to challenge based on mortalities and quantitative cultures of kidneys, with mice from strains C57BL/6J and BALB/cByJ showing the most resistance; mice from strains A/J, C3H/HeJ, and CBA/J showing moderate susceptibility; and mice from strain DBA/2J showing the highest degree of susceptibility to challenge. Unimmunized mice from strains C57BL/6J and BALB/cByJ did not produce detectable levels of Candida-specific antibody by the end of the 28-day observation period when challenged intravenously, but the other strains did. Immunized mice showed a degree of protection to challenge, with all groups except mice from strain BALB/cByJ showing a reduction of two to three log units in the level of colonization in their kidneys and all strains producing significant levels of antibody. Additionally, the immunized mice of all strains developed substantial levels of delayed-type hypersensitivity and demonstrated nearly identical lymphocyte proliferative responses to Candida antigens. The results indicate that resistance to systemic candidiasis is dependent upon a combination of innate factors, predominately an intact complement system, and the acquisition of an immune response, most likely of a cell-mediated type. Additionally, the findings suggest that genetic control of acquired resistance to C. albicans may not be associated with the H-2 complex.

In vitro phagocytosis of Candida albicans by peritoneal mouse macrophages

The ability of sensitized mouse peritoneal macrophages to phagocytose and inhibit Candida albicans was studied in an in vitro system. Mice were sensitized to C. albicans by intraperitoneal infection with viable organisms or by intracutaneous injection of heat-inactivated cells in Freund complete adjuvant. Development of delayed hypersensitivity to C. albicans was evaluated by footpad tests with cytoplasmic and cell wall antigens as well as by macrophage migration inhibition by these antigens and by whole heat-inactivated cells. Inhibition of macrophage migration by heat-inactivated cells was significantly greater when the mice were sensitized by viable organisms. The macrophages from these mice were also larger and showed a greaer ability to inhibit germ tube production by phagocytosed yeasts. This suggests that macrophages may play a protective role in infection by C. albicans.

Biochemical examination of sera during systemic Candida infection in mice

Candida pathogenesis was examined by intravenous challenge of mice with either C. albicans or C. guilliermondii. Animals were moribund 12 h postchallenge with C. albicans and were found to have the greatest number of organisms in the heart and kidney, severe interstitial myocarditis, and elevated serum levels of blood urea nitrogen, creatine phosphokinase, serum glutamic oxalacetic transaminase, serum glutamic pyruvic transaminase, and lactic dehydrogenase. In contrast, challenge with C. guilliermondii resulted in a significantly lower renal census, no myocarditis, and no significant change in the concentration of these serum constituents. Challenge with nonviable C. albicans did not produce the effects observed with viable organisms. Moreover, challenge with filamentous C. albicans resulted in biochemical alterations of lower magnitude and in lower mortality rates. These results indicated that altered serum biochemistries were correlated with the histopathology of fatal Candida infection and that there were distinct differences with C. guilliermondii and the dimorphic phases of C. albicans.

Immunity to experimental renal candidiasis in rats

Germfree rats were found to be more susceptible to intravenous challenge with Candida albicans than were conventional rats. The resistance of conventional rats could be overcome by increasing the challenge dose. The resistance of the germfree rat was enhanced by vaccination with Formalin-killed C. albicans in complete Freund adjuvant, complete Freund adjuvant, or incomplete Freund adjuvant. These results, and histological evidence obtained from infected gnotobiotic rats, provided further information on the mechanism of resistance to the disseminated form of candidiasis.

Cellular elements in the resistance to candida infection in mice. I. Contribution of T lymphocytes and phagocytes at various stages of infection

Live organisms (cfu) of Candida albicans per organ were counted 1 hr and 1 to 20 days after an intravenous inoculation into various groups of mice which had distinct levels of immunologic or non-immunologic defense mechanisms. a) The number of cfu in the liver decreased progressively in normal mice, but those in the kidney maintained a constant level during the observation period. b) The number of cfu in the liver decreased progressively also in nude mice. In their kidneys, however, cfu increased progressively at a late stage of infection. c) In lethally irradiated AKR of nude mice in which phagocyte functions were severely depressed, the number of cfu increased progressively in both liver and kidney from the initial stage of infection. d) In immunized AKR mice, growth of C. albicans was suppressed at late stages of infection. Such protective immunity could be transferred partly with immune lymphoid cells but not with hyperimmune serum in the experimental system employed. In protection against candida infection, non-immune phagocytosis and T cell-mediated immunity appear to be required at the early and late stages of infection, respectively.

Experimental Candida albicans infection in conventional mice and germfree rats

Swiss-Webster white mice were intravenously infected with various doses of Candida albicans, and the viable units in their spleens, livers, lungs, and kidneys were determined at various intervals after challenge. The results showed that C. albicans multiplied to a greater extent in the kidneys of mice than in their spleens, lungs, or livers. The infection in mice was chronic; increasing numbers of C. albicans were observed in their kidneys until about 17 to 24 days postchallenge. Clearance of C. albicans from infected kidneys was not symmetrical, since the number of viable C. albicans in one kidney did not coincide with the viable counts observed in the opposite kidney of that same animal. Male and female mice did not differ in their overall susceptibility (50% lethal dose test) or in the number of viable C. albicans in the kidneys at various time intervals after infection. C. albicans also multiplied in the kidneys of germfree rats; however, the peak of the C. albicans infection in their kidneys occurred earlier than in those of conventional mice.

Acquired immunity to Aspergillus fumigatus

In mice preinfected with Aspergillus fumigatus for greater than or equal to days, administration of cortisone failed to stimulate mycelial growth. The liver and heart of mice preinfected for 14 days resisted infection after a cortisone + conidia challenge.