Although several immunological abnormalities may be present in pigeon hypersensitivity pneumonitis (HP), few specific hallmarks have been described.
To determine whether the presence of rheumatoid factor (RF) could be useful to discriminate pigeon HP from asymptomatic breeders (AB) and other interstitial lung diseases.
Fifty-three patients with pigeon HP, 47 AB, 31 idiopathic pulmonary fibrosis (IPF) patients and a rheumatoid arthritis (RA) group were studied. IgM RF was determined through enzyme-linked immunosorbent assay (ELISA) and western blot using human IgG and IgG Fc fragment as antigens. IgG and IgA anti-avian antibodies (AA) against pigeon serum antigen were also measured. The use of F(ab')2 fraction of peroxidase-labelled anti-human immunoglobulins prevented endogenous interferences. Possible cross-binding of RF with avian antigens and the reactivity against human IgG by AA were studied.
RF tests were frequently positive in HP (52.8%) in comparison to AB (4.2%) and IPF (12.9%; P = 2.6 x 10-10 and 4.1 x 10-5). Therefore, the presence of RF in pigeon HP showed a sensitivity of 52% and was highly specific considering the results of AB and IPF (95 and 87%, respectively). The RA group revealed positive RF but negative AA tests. RF activity was confirmed through western blot using purified IgG Fc fragment. Overlapping levels of IgG and IgA AA were found in HP and AB. The frequency of AA was low in IPF. The cross-reaction of RF with avian antigens was excluded, and no reactivity against human IgG by AA was detected. Other endogenous interferences were ruled out.
No single immunological test may definitively distinguish pigeon HP from AB and other interstitial lung disorders; however, positive RF, together with high AA levels, seems to be useful in differentiating the diagnosis.