Enhancement of MHC class II antigen expression by exposure to Candida albicans

Immunopathogenesis of oropharyngeal candidiasis in human immunodeficiency virus infection

Oropharyngeal and esophageal candidiases remain significant causes of morbidity in human immunodeficiency virus (HIV)-infected patients, despite the dramatic ability of antiretroviral therapy to reconstitute immunity. Notable advances have been achieved in understanding, at the molecular level, the relationships between the progression of HIV infection, the acquisition, maintenance, and clonality of oral candidal populations, and the emergence of antifungal resistance. However, the critical immunological defects which are responsible for the onset and maintenance of mucosal candidiasis in patients with HIV infection have not been elucidated. The devastating impact of HIV infection on mucosal Langerhans' cell and CD4(+) cell populations is most probably central to the pathogenesis of mucosal candidiasis in HIV-infected patients. However, these defects may be partly compensated by preserved host defense mechanisms (calprotectin, keratinocytes, CD8(+) T cells, and phagocytes) which, individually or together, may limit Candida albicans proliferation to the superficial mucosa. The availability of CD4C/HIV transgenic mice expressing HIV-1 in immune cells has provided the opportunity to devise a novel model of mucosal candidiasis that closely mimics the clinical and pathological features of candidal infection in human HIV infection. These transgenic mice allow, for the first time, a precise cause-and-effect analysis of the immunopathogenesis of mucosal candidiasis in HIV infection under controlled conditions in a small laboratory animal.

Activated CD8+ T cells are involved in elimination of Candida albicans from the livers of mice

We have investigated the course of infection of Balb/c mice with Candida albicans. After intravenous infection of mice, the yeasts were evenly distributed in the liver sections. There was a 90% reduction in the yeasts found within 7 days after infection. This reduction was accompanied by an increase in the number of phagocytic cells (Mac-1+, Gr-1+) in cellular infiltrates around the yeast cells. Furthermore, both CD4+ and CD8+ T lymphocytes were found in these pseudogranulomata, with the CD8+ cells in the periphery. Peak amounts of the cell types investigated were found at days 5 and 6 post infection, with an increased expression of receptors for interleukin 2 (IL-2R) on the surface of CD8+ cells. At day 14 of infection, the same levels as those in control mice were reached. At this time, the yeasts were virtually eliminated from the liver. By using simultaneous detection of cell surface markers and yeast cells in immunohistology, these data demonstrate the close association of fungal cells, phagocytes, TH and TC cells in pseudogranulomata during elimination of Candida albicans from the livers of mice.

Production and function of cytokines in natural and acquired immunity to Candida albicans infection

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.