IMMUNOLOGICAL ASPECTS OF ORAL CANDIDIASIS

Immunity to Candida infections in human beings is complex because of the different types of candidiasis, the different forms of Candida itself, and the interrelationships between the mucosal and systemic immune systems. Mucosal infection is by far the most common type of candidiasis, but systemic infection can also occur and the mechanisms for each may be quite different. In the oral cavity there are four main types of candidiasis, and hyphal and yeast forms of Candida may be present with both common and unique antigens. Humoral immunity is represented by salivary antibodies of the mucosal immune system and serum antibodies in the mucosa. Cell-mediated immunity may play a role particularly in chronic hyperplastic candidiasis. Salivary antibodies have been shown to inhibit adherence of Candida to buccal epithelial cells and to be protective in animal models. Serum antibodies against a 47kD antigen have been shown to correlate with protection and recovery from systemic candidiasis, but there is little evidence for a role of serum antibody in protection against infection of the oral cavity. In in vitro studies, both macrophages and polymorphonuclear leukocytes can kill yeast forms and inhibit hyphal forms of Candida and because chronic hyperplastic candidiasis is associated with intraepithelial polymorphonuclear leukocytes, these cells could be operative in vivo. Saliva contains a number of antifungal proteins including histatins and calprotectin that could act synergistically with specific factors. It is possible that cellular factors provide the main form of defense against mucocutaneous infection, whereas humoral factors play a larger role in the prevention of dissemination of Candida infections. Nonspecific mechanisms such as macrophage and polymorphonuclear leukocytes may play a supporting role in both types of infection.