BACKGROUNDCoccidioidomycosis ranges from self-limiting uncomplicated Valley fever (UVF) in most cases to life-threatening disseminated coccidioidomycosis (DCM) in rare individuals. A few patterns of immunologic deficits allowing for dissemination have been identified, although the specific defects in most individuals with DCM remain undefined. We hypothesized that chronic antigen exposure in DCM engenders a state of T cell exhaustion.METHODSFrom a cohort of over 300 individuals with confirmed diagnoses of coccidioidomycosis, circulating T cell phenotypes were characterized via flow cytometry and Coccidioides-specific T cell responses were measured by activation-induced marker (AIM) assay.RESULTSMale sex was significantly associated with disseminated disease (OR 2.5, 95% CI 1.5-4.0). A majority (52%) of individuals showed Coccidioides-specific T cell responses in our AIM assay. We noted a significant difference in patients sampled in the first year of diagnosis, where only 8% of patients with DCM had T cell responses during this time, as compared with 44% of individuals with UVF (P = 0.04). Among DCM patients with detectable AIM responses, CD4+ T cells demonstrated an exhausted phenotype with elevated PD-1 expression compared with UVF individuals. In vitro PD-1 blockade augmented IFN-γ production in most tested individuals with DCM.CONCLUSIONThese findings suggest that dissemination may occur in some individuals during a period of impaired antigen-specific T cell activity. Importantly, these responses can be augmented in vitro by PD-1-blocking antibodies, supporting further study of immune checkpoint therapy as an adjunct to antifungal treatment in disseminated coccidioidomycosis.FUNDINGNational Institute of Allergy and Infectious Diseases grants U19 AI166059 and R21 AI149654 and University of California Office of the President grant VFR-19-633386.

Coccidioides species are thermally dimorphic fungal pathogens that cause coccidioidomycosis (Valley Fever) primarily in North and South America. Coccidioides grow as hyphae that differentiate into arthroconidia, which can be aerosolized upon soil disturbance, and inhaled by the mammalian host to cause pulmonary infections with occasional dissemination to other organs. In the context of mouse models, current methods of infection include intranasal, intravenous, and intraperitoneal delivery of the arthroconidia into mice. To explore an aerosol route of infection, we compared the intranasal method with aerosolization using the Glass-Col Inhalation Exposure System (IES). Infection with a dose of 2 × 10⁶ CFU/mL, nebulized in 5 mL of PBS, but not in water, was able to infect mice, albeit inconsistently, compared to intranasal challenge. Arthroconidia were detected inside the IES after the nebulization and decontamination cycles. These studies highlight some of the challenges with aerosolization of Coccidioides arthroconidia and serve as a reminder about biosafety considerations for use of the IES to aerosolize pathogens.

Coccidioides is a dimorphic fungal pathogen that grows as a mold in soil and produces infectious arthroconidia. Inhaled arthroconidia transition to spherules containing endospores in mammalian hosts. How distinct developmental forms of Coccidioides interact with immune cells remains poorly defined. Here, we show that arthroconidia activates TLR2 and induces NLRP3-pyrin inflammasomes in macrophages, while ferroptotic signaling promotes arthroconidia killing. Upon transition to spherules, only ruptured spherules—not intact ones—trigger IL-1β production through NLRP3-pyrin inflammasomes and GSDMD-GSDME pores. A TLR2-NLRP3-pyrin-IL-18 axis in macrophages promotes spherule growth. Endospores activate NLRP3 but not pyrin inflammasomes. Caspase-1-deficient mice show improved disease tolerance to coccidioidomycosis despite equivalent fungal burdens, correlating with enhanced neutrophil extracellular trap formation in lung granulomas. Neutrophils respond to spherules through NLRP3-pyrin inflammasomes, GSDMD-GSDME, and MLKL. Together, these findings reveal that Coccidioides morphotypes elicit distinct yet overlapping immune programs, coordinating inflammasome activation and regulated cell death to shape host-pathogen dynamics.