Hypersensitivity pneumonitis and antigen identification--An alternate approach

Identification of the causal antigen for patients with hypersensitivity pneumonitis (HP) is challenging in a standard clinical setting. The purpose of this pilot study was to determine whether it was possible to evaluate the home/workplace of patients, and identify the causal antigen.

Using a case-control study design we compared the presence of antibody to antigen collected in the environment of individuals with HP and controls consisting of family members/co-workers. Based on patient interviews, homes/workplaces were evaluated and suspected sources of antigen collected for use in immunoassays.

Nineteen individuals with HP participated with 15 classified as having fibrotic disease. Up to 54 bulk samples were collected from each patient's environment, with multiple isolates (antigens) cultured from each. Of the seven individuals who tested positive to one or more environmental samples, three had a positive response to more than 1 antigen from the environmental sample (range 1-9). Twelve individuals tested positive to antigen(s) on a standard panel, with only one overlapping with the antigen from the home/workplace sample. A significant association existed between results of interviews/site evaluations, and ability to collect antigen eliciting a positive response (p < 0.001).

Antigen identification was successful for patients with 'active' disease. Antigens for which patients test positive on standard panels may not be present in their environment. One benefit to patient-centered testing is the ability to develop recommendations specific to their environment. As most individuals tested positive for >1 antigen, further investigation is warranted to determine the actual antigen responsible for disease.