Secreted<i>Candida parapsilosis</i>lipase modulates the immune response of primary human macrophages

Abstract

Candida parapsilosis is an important opportunistic pathogen with increasing prevalence. Extracellular lipases have been shown to play an important role in the virulence of pathogenic Candida species. However, studying the role of secreted lipase in C. albicans is challenging due to the lack of a mutant strain deficient in all 10 lipase genes. In contrast, we have previously constructed a lipase mutant C. parapsilosis strain lacking both CpLIP1 and CpLIP2, and shown that it has significantly decreased virulence in various infection models, and is killed more efficiently by mouse macrophages. In the present study, we compared the response of human peripheral blood monocyte-derived macrophages to a wild type (wt) as well as a lipase-deficient (lip(-/-)) C. parapsilosis strain that has been previously established in our lab. Although macrophages phagocytosed both strains with similar efficiency, lipase mutants were killed more efficiently according to fluorescent microscopic analysis. The more efficient killing of lip(-/-) cells was confirmed by CFU-determinations. Phagocytosis of wt and lip(-/-)C. parapsilosis was also examined by flow cytometry, revealing that both strains were internelized to the similar extent by macrophages. Additionally, quantitative imaging analysis revealed that the rate of phagolysosome fusion was higher in case of lip(-/-)C. parapsilosis. Interestingly, macrophages stimulated with lip(-/-)C. parapsilosis showed at least 1.5-fold higher expression of TNFα, IL-1β, IL-6, IL-8, and PTGS-2 after 12 h compared with those infected with wt C. parapsilosis, as determined by qRT-PCR. Furthermore, the lip(-/-)C. parapsilosis strain induced significantly higher TNFα, IL-1β, IL-6, and IL-10 protein production in macrophages after 24 h compared with the wt strain. These findings confirm the role of fungal lipases as important virulence factors during C. parapsilosis infection.