Cryptogenic fibrosing alveolitis: have we made any progress?

Private specificities can dominate the humoral response to self-antigens in patients with cryptogenic fibrosing alveolitis

BACKGROUND

The pathogenetic mechanisms that underlie the interstitial lung disease cryptogenic fibrosing alveolitis (CFA) may involve an immunological reaction to unidentified antigens in the lung, resulting in tissue damage.

METHOD

In order to identify the range of target autoantigens, we used expression cloning, employing serum from an index patient as the probe against an expressed cDNA library that was derived from a tumour cell line. We screened over 5 x 105 recombinants and obtained sequence information on three antigens that had provoked strong responses with immunoglobulin heavy chain class switching, presumably as a consequence of T-cell recognition.

RESULTS

All of the antigens were identifiable by comparison with sequence data from the US National Center for Biotechnology Information. Alanyl tRNA synthetase (ATS) was picked on six occasions; five of these incidences reflected independent recombination events, indicating that the library was not biased. Antibodies to ATS (anti-PL-12) represent the most common reactivity that defines the antisynthetase syndrome, which is typically expressed as polymyositis, dermatomyositis and interstitial lung disease (ILD). The index patient never showed symptoms other than those associated with alveolitis, even though sera obtained from him over a period of 2 years contained antibodies with the same specificity. Autoantibodies to ATS were never detected in serial bleeds from 11 other patients with CFA, and neither did we detect antibodies to the other two antigens identified from the serum of the index patient.

CONCLUSION

The humoral response in patients with CFA can be dominated by autoantibodies with private specificities. This suggests that the antibodies are epiphenomenal and are a secondary feature of tissue damage induced by some other mechanism.