Candida albicans adhesins: Biochemical aspects and virulence

The recognition of host cells by the pathogenic yeast, Candida albicans, is probably an essential step in the pathogenesis of disease development. The interaction of yeast and hyphal mannoproteins with host cell receptors has been studied by a number of laboratories. C. albicans recognizes a variety of host cells as well as host cell extracellular matrix proteins. This observation is not unexpected given the number of sites within and on the body which can be colonized and infected by the organism. Indeed, it would appear that C. albicans has evolved a number of ways in which it recognizes the host. This statement is made with the qualification that the organism uses other processes to infect, such as morphogenesis, phenotypic switching and the production of invasive enzymes, including secreted aspartyl proteases and phosholipases. Recognition of epithelial cells is accomplished through cell surface mannoproteins (adhesins) which bind to carbohydrate-containing receptors. The number of such mannoproteins is not known; pro adhesins exist. The organism also binds to keratinocytes, endothelial cells and matrix proteins, such as fibronectin, laminin, collagen and entactin, and, as such, appears to have a integrin-like cell surface adhesin. In most cases, the adhesin for each of these host proteins is a mannoprotein. The biochemistry of the candidal adhesins has been extensively studied. However, molecular analyses of the encoding genes is only now being studied. Thus, until clean, genetic analyses are complete and strains lacking an adhesin function are constructed, a direct role for the adhesins in pathogenesis can only be inferred. At present, spontaneous, non-adhering strains of the organism have been described which are avirulent in animal models of candidiasis. However, these data only suggest a role for adherence; future studies should be directed towards resolving questions about the role of these proteins in pathogenesis.