The frequency of
infection and death due to various Candida species has increased steadily during the past decade, with mucocutaneous candidal
infections as a common problem in the immunocompromised host. Mononuclear phagocytes are important in phagocytosis of this organism. In areas where there are low levels of
opsonins, the macrophage-specific
mannose receptor plays a dominant role in mediating Candida albicans ingestion. Following receptor-mediated
infection, the host macrophage produces inflammatory
cytokines and mediators that lead to ultimate killing of the invading Candida.
Infection of macrophages by pathogens often leads to altered function that might effect their subsequent host defense properties. For example, function of both the
complement receptor type 3 and the
mannose receptor are down-regulated following exposure to pathogens or pathogen-derived products. In the current study, we have examined the down-regulation of
mannose receptor expression following
Candida infection and have investigated possible mechanisms that might be involved.
Mannose receptor activity was decreased following 24 h postinfection with Candida. Both
tumor necrosis factor and
nitric oxide were produced during the
infection, and inhibition of the these mediators partially blocked the effect on the receptor.
Infection with Candida also inhibited the ability of
dexamethasone to up-regulate
mannose receptor expression. Finally,
mannose receptor protein turnover was accelerated in Candida-infected macrophages. We conclude that Candida down-regulates one of the receptors involved in its internalization through a combination of production of modulatory molecules and enhanced receptor degradation. These results support the hypothesis that pathogens that infect macrophages have the ability to alter the phagocytic pathways available for subsequent host defense.