Interaction of Zygomycetes with innate immune cells reconsidered with respect to ecology, morphology, evolution and infection biology: a mini-review.

Zygomycetes are saprophytic fungi found ubiquitously in nature. Generally, fungi are considered as the most common microbes encountered by mammalian hosts due to its ubiquity in nature. Among the fungi, the Zygomycetes represent the most basal terrestrial lineage which can cause infections in humans. They comprise two orders, the Mucorales and the Entomophthorales, which contain human pathogenic species. Members of the Mucorales are responsible for mucormycosis; the second most common mould fungi infection in the world and infection with members of the Entomophthorales can result in basidiobolomycosis and conidiobolomycosis. However, the infection does not occur frequently as we have efficient barriers from immune system against the fungal invasion. In this review, a summary is provided on the current literature available on innate immune cells such as polymorphonuclear leucocytes, macrophages, etc. and their interaction with zygomycetes.

Virulent strain of Lichtheimia corymbifera shows increased phagocytosis by macrophages as revealed by automated microscopy image analysis.

Lichtheimia corymbifera is a ubiquitous soilborne zygomycete fungus, which is an opportunistic human pathogen in immunocompromised patients. The fungus can cause life-threatening diseases by attacking the lung during early stages of invasion and by disseminating during later phases causing systemic infection. Since infections have drastically increased during the last decades, it is a major goal to investigate the mechanisms underlying pathogenicity of L. corymbifera. One of the first barriers, which the fungus needs to cope with in the lung tissue, is phagocytosis by alveolar macrophages. Here, we report on phagocytosis assays for murine alveolar macrophages co-incubated with resting, swollen and opsonised spores of a virulent and an attenuated L. corymbifera strain. A major finding of this study is the significantly increased phagocytosis ratio of the virulent strain if compared to the attenuated strain. We quantify the phagocytosis by performing automated analysis of fluorescence microscopy images and by computing ratios for (i) fungal phagocytosis, (ii) fungal adhesion to phagocytes and (iii) fungal aggregation and spore cluster distribution in space. Automation of the image analysis yields objective results that overcome the disadvantages of manual analyses being time consuming, error-prone and subjective. Therefore, it can be expected that automated image analysis of confrontation assays will play a crucial role in future investigations of host-pathogen interactions.