Figure 1.

Fungal dimorphism presents challenges for immune detection and activation. Early infection: Coccidioides is vulnerable to immune detection during early infection due to the smaller size (2–5 μM) and SOWgp expression which is detected via Dectin-1 and TLR2 on innate immune cells. These interactions mediate clearance via phagocytosis and reactive oxide species production. Later infection: As Coccidioides sporulates, it secretes MEP1 which digests SOWgp from the fungal surface, hampering immune detection. Spherules induce arginase expression in host tissues, suppressing NOS/NO production via an unknown mechanism, contributing to immune suppression.