Clinicoradiological Profile, Immunopathology, and 1-year Outcomes in Biopsy-proven Hypersensitivity Pneumonitis: A Prospective Cohort Study

individual susceptibility, and the immune response elicited.Traditionally, the disease has been classified into acute, subacute, and chronic forms.More recently, Vasakova et al. proposed a revised classification system that divides HP into acute/inflammatory IntroductIonHypersensitivity pneumonitis (HP) is an immune-driven lung disorder caused by repeated inhalation of environmental antigens.Initially recognized by Ramazzini as an occupational hazard, 1 the disease's underlying mechanisms have since been extensively studied and clarified. 2Currently, >200 antigens have been implicated in HP development.These are primarily proteins or glycoproteins originating from fungal, bacterial, or animal sources, although certain low molecular weight chemical agents have also been identified as triggers. [2][3]][4] The incidence and prevalence of HP show significant variation globally, largely due to the absence of standardized international diagnostic criteria, as well as differences in seasonal patterns, geographic factors, and host susceptibility.In Western countries, the reported incidence of HP ranges between 0.3 and 0.9 cases per 1,00,000 people. 5Within three European nations, HP represents approximately 4-15% of all interstitial lung disease (ILD) cases. 6Occupational exposure studies have identified HP in 19% of farmers working with moldy hay and between 6 and 20% of individuals affected by bird fancier's lung due to contact with bird droppings. 7,8In India, various investigations indicate that HP constitutes 2.4-10.7% of ILD cases. 9,10According to the Indian ILD registry, HP is the most frequently diagnosed newly onset ILD, accounting for 47% of cases. 11he clinical presentation of HP varies according to factors such as the nature of the antigen, the level and length of exposure,