The Role of Serum IgG Precipitins against Six Typical Organic Antigens Involved in Hypersensitivity Pneumonitis: A 10-Year Retrospective Study of a Referral Interstitial Lung Disease Centre

Hypersensitivity pneumonitis (HP) represents the third common interstitial lung disease caused by an exaggerated immune response following the inhalation of organic and/or chemical environmental antigens. The aim of this study was to determine the cut-off values of specific IgG antibodies (named precipitins) and their association with clinical data in the diagnosis of HP. In this 10-year retrospective study, the IgG concentrations against six antigens, Penicillium chrysogenum/notatum, Aspergillus fumigatus, Alternaria alternata, Aspergillus niger, Micropolyspora faeni, and pigeon droppings, were retrieved. The controlled group was made of 1516 healthy subjects without diagnosis of lung pathologies, while the case group consisted of 54 individuals affected by HP. Considering all six IgG antibodies together and the 97.5% percentiles determined in the control group, 30 of 54 subjects (56%) had one or more positive precipitins. In these patients, the major frequencies found were IgG antibodies against pigeon droppings, followed by Penicillium chrysogenum/notatum and Aspergillus niger. Although the sensitivity of serum precipitins depends on the population enrolled and the method used, the cut-off values determined in this study can be a valuable tool for clinicians in the diagnosis of HP, in eliminating the antigens responsible from the environment, and in establishing more specific IgG panels.