Kinetic studies of Candida parapsilosis phagocytosis by macrophages and detection of intracellular survival mechanisms

Abstract

Even though the number of Candida infections due to non-albicans species like C. parapsilosis has been increasing, little is known about their pathomechanisms. Certain aspects of C. parapsilosis and host interactions have already been investigated; however we lack information about the innate cellular responses toward this species. The aim of our project was to dissect and compare the phagocytosis of C. parapsilosis to C. albicans and to another Candida species C. glabrata by murine and human macrophages by live cell video microscopy. We broke down the phagocytic process into three stages: macrophage migration, engulfment of fungal cells and host cell killing after the uptake. Our results showed increased macrophage migration toward C. parapsilosis and we observed differences during the engulfment processes when comparing the three species. The engulfment time of C. parapsilosis was comparable to that of C. albicans regardless of the pseudohypha length and spatial orientation relative to phagocytes, while the rate of host cell killing and the overall uptake regarding C. parapsilosis showed similarities mainly with C. glabrata. Furthermore, we observed difference between human and murine phagocytes in the uptake of C. parapsilosis. UV-treatment of fungal cells had varied effects on phagocytosis dependent upon which Candida strain was used. Besides statistical analysis, live cell imaging videos showed that this species similarly to the other two also has the ability to survive in host cells via the following mechanisms: yeast replication, and pseudohypha growth inside of phagocytes, exocytosis of fungal cells and also abortion of host cell mitosis following the uptake. According to our knowledge this is the first study that provides a thorough examination of C. parapsilosis phagocytosis and reports intracellular survival mechanisms associated with this species.

Candida parapsilosis: from Genes to the Bedside

“…Constructs suitable for PCR-mediated C-terminal tagging of target genes with green, yellow, or mCherry fluorescent proteins using NAT1 as the selectable marker are also available (114). GFP-labeled strains of C. parapsilosis have already been used to study phagocytosis of macrophages (115). selectable markers were therefore developed by modifying the coding sequence of existing systems to replace CTG codons.…”

“…parapsilosis pseudohyphae contribute to virulence. Although in terms of uptake, host phagocytic cells do not differentiate between yeast and pseudohyphal forms, C. parapsilosis pseudohyphae are more resistant to killing by macrophages and induce higher levels of host cell damage in vitro, thus contributing to the species' pathogenicity (115,168). Therefore, the underlying molecular mechanisms regulating morphology transition have also been investigated.…”

“…To date, four secreted-lipase-encoding genes have been identified in the genome of C. parapsilosis, although only two (LIP1 and LIP2) have been confirmed to encode functionally active proteins (17). Deletion of CpLIP1 and CpLIP2 revealed their role in mechanisms required for successful host invasion, including nutrient acquisition and sustainability in a lipid-rich environment, enhancement of adhesion and biofilm formation, suppression of both cellular and humoral immune responses during infection, promotion of survival after phagocytosis, and progression of host tissue invasion (17,115,204). Furthermore, the lipase inhibitor ebelactone B and aspirin also protect reconstituted human tissue (RHT) in the setting of C. parapsilosis infection, which supports a role for secreted lipases in pathogenesis (203,205).…”

Beyond Candida albicans: Mechanisms of immunity to non-albicans Candida species

“…More efficient phagocytosis and killing of certain NAC species compared to C. albicans by macrophages has been reported, similar to neutrophils. C. parapsilosis is killed more efficiently than C. albicans , a process that involves production of oxygen radicals [96, 97]. Similarly, C. glabrata is phagocytosed at higher rates by macrophages than C. albicans , which was more lethal to macrophages [88, 97, 98].…”

“…C. parapsilosis is killed more efficiently than C. albicans , a process that involves production of oxygen radicals [96, 97]. Similarly, C. glabrata is phagocytosed at higher rates by macrophages than C. albicans , which was more lethal to macrophages [88, 97, 98]. In this regard, macrophage phagocytosis rate of C. albicans is dependent on fungal morphology, and C. albicans hyphae can lyse macrophages [98–100].…”