Coccidioides posadasii antigens (Ag2/PRA (proline-rich antigen))

Coccidioides posadasii antigens are immunogenic components primarily derived from the pathogenic dimorphic fungus C. posadasii, which causes coccidioidomycosis (Valley Fever), an endemic respiratory infection in arid regions of North, Central, and South America. Key antigens like the proline-rich antigen (PRA or Ag2) exhibit endoglucanase activity and play a critical role in spherule cell-wall morphogenesis during tissue invasion, with increased expression during fungal development in the host. These antigens, including β-glucans in spherule walls comprising ~60% dry weight, are recognized by host pattern recognition receptors such as Dectin-1 and TLR2 on macrophages, triggering MyD88-dependent proinflammatory cytokine production (TNF-α, IL-6, IL-12, MIP-2) essential for innate immunity. Dendritic cells bind and process spherules for antigen presentation, stimulating both T- and B-cell responses. Antigens from strains like Silveira serve as sources for diagnostic tools (coccidioidin, spherulin) and vaccine studies, though no approved therapeutic drugs directly target them. In disease, they contribute to pathogenesis by modulating immune evasion in the spherule phase, the tissue-invasive form.

Other names

proline-rich antigen (PRA)Ag2/PRASOWgp