Fungal stimulation induces a specific Th1-like immune response in hypersensitivity pneumonitis patients

Identifying the inciting antigen in hypersensitivity pneumonitis (HP) is critical to obtain a confident diagnosis and improve clinical outcomes, as exposure avoidance may prevent fibrotic progression. However, the culprit exposure is often not identified. Molds are considered a putative source of triggering antigens that have been associated with the development of HP. The aim of this work is to establish an association between the high HP incidence in Portugal and prolonged domestic exposure to molds, through the assessment of specific fungi reactive T cells in HP patients. Air samples were collected from patients’ homes. <italic>Cladosporium</italic> and <italic>Penicillium</italic> spp. were shown to be the most prevalent fungi, and <italic>Aspergillus fumigatus</italic>, <italic>A. niger</italic>, and <italic>Rhizopus</italic> spp. showed up in higher amounts indoors rather than in outdoor environment. Peripheral blood mononuclear cells from HP patients and healthy co-inhabitants were stimulated with fungal cocktails comprising conidia from the selected fungi. Upon stimulation, we observed a strong T cell proliferative response towards these antigens, as well as highly increased IFN-γ secretion in HP patients in comparison with co-inhabitants. When cells from patients under diagnosis workup were stimulated with the same fungal antigens, the observed specific T cell response was similar to that of HP-diagnosed patients. According to these results, HP patients developed a specific and intense Th1-like immune response towards a common fungal cocktail, avoiding the need for recurring house inspections. Assessing mold-specific response will fulfill a clinical need in exposure identification, therefore contributing to a higher confidence HP diagnosis.