Elimination of mouse splenic macrophages correlates with increased susceptibility to experimental disseminated candidiasis

To evaluate the role of macrophages in experimental disseminated candidiasis, mouse splenic macrophages were eliminated by i.v. delivery of liposome-entrapped dichloromethylene diphosphonate (L-Cl2MDP). Splenic tissue sections that were immunoperoxidase-stained with mAbs against marginal zone macrophages (MONTS-4), red pulp macrophages (SK39), and neutrophils (SK208) showed that 3 days after L-Cl2MDP treatment, macrophages but not neutrophils were depleted, and circulating neutrophils responded normally to an irritated peritoneum and showed normal phagocytic ability. That is, in response to thioglycollate in the peritoneum, neutrophils migrated in normal numbers to the peritoneal cavity and expressed the normal activation phenotype of high Mac-1 and low Mel-14 Ag levels. These neutrophils also showed normal ability to ingest Candida albicans yeast cells in both in vitro and in vivo assays. However, the spleens from L-Cl2MDP-treated mice lost their ability to bind yeast, which agrees with our previous findings that yeast cells bind specifically to marginal zone macrophages. When macrophage-depleted were systemically challenged with C. albicans, clearance of viable fungal elements from blood was slower, their kidneys had higher recoverable CFU, and both BALB/cByJ and congenitally thymic-deficient (nude) mouse strains did not survive as long as control mice. Mice given L-Cl2MDP recovered most of their macrophage function by 56 days and became normal in their resistance to C. albicans. These results indicate that macrophages play an important role in host resistance to experimental disseminated candidiasis, but the mechanism does not appear to involve T cell functions.