Early Interaction of Alternaria infectoria Conidia with Macrophages

Fungi of the genus Alternaria are ubiquitous indoor and outdoor airborne agents, and individuals are daily exposed to their spores. Although its importance in human infections and, particularly in respiratory allergies, there are no studies of how Alternaria spp. spores interact with host cells. Our aim was to study the early interaction of Alternaria infectoria spores with macrophages, the first line of immune defense. RAW 264.7 macrophages were infected with A. infectoria conidia, and the internalization and viability of conidia once inside the macrophages were quantified during the first 6 h of interaction. Live cell imaging was used to study the dynamics of this interaction. TNF-α production was quantified by relative gene expression, and the concentration of other cytokines (IL-1α, IL-1β, IL-6, IL-4, IL-10, IL-17, GM-CSF and INF-γ) and a chemokine, MIP-1α, was quantified by ELISA. Conidia were rapidly internalized by macrophages, with approximately half internalized after 30 min of interaction. During the first 6 h of interaction, macrophages retained the ability to mitotically divide while containing internalized conidia. The classical macrophage-activated morphology was absent in macrophages infected with conidia, and TNF-α and other cytokines and chemokines failed to be produced. Thus, macrophages are able to efficiently phagocyte A. infectoria conidia, but, during the first 6 h, no effective antifungal response is triggered, therefore promoting the residence of these fungal conidia inside the macrophages.