Abstract
The pathogenic yeast Cryptococcus neoformans produces a laccase enzyme (CNLAC1), which catalyzes the synthesis of melanin in the presence of phenolic compounds. A number of genes have been implicated in the regulation of laccase and melanization, including IPC1, GPA1, MET3, and STE12. Albino mutants derived from random mutagenesis techniques may contain mutations in genes that regulate multiple virulence factors, including CNLAC1. The goal of our study is to investigate the role of CNLAC1 in virulence and evasion of pulmonary host defenses after infection via the respiratory tract. Using a set of congenic laccase-positive (2E-TUC-4) and laccase-deficient (2E-TU-4) strains, we found that both strains are avirulent at a lower dose (10(4) CFU/mouse) in mice. After the infectious dose was increased to 10(6) CFU/mouse, 70% mortality was observed in mice infected with 2E-TUC-4 compared to no mortality in mice infected with 2E-TU-4 at day 30 postinfection. This observation confirms the requirement for CNLAC1 in virulence. Interestingly, we observed no differences between the two strains in pulmonary growth or in elicitation of cellular immune responses in the lung. The only measurable defect of 2E-TU-4 was in dissemination to extrapulmonary sites. To examine the role of CNLAC1 in dissemination, mice were infected intravenously. By week 3 postinfection, equal numbers of strains 2E-TUC-4 and 2E-TU-4 were recovered from the brain and spleen. This observation indicates that CNLAC1 facilitates escape from the lung, but not growth in the lungs or brain, and suggests a novel role for CNLAC1 in virulence during an infection aquired via the respiratory tract.