HLA-A, B and DR antigens and properdin factor B allotypes in Caplan's syndrome.

Seventy-nine cases of Caplan's lung were typed for HLA-A and B antigens. The antigen Bw45 was present only in those patients with rheumatoid factor and was of significantly higher frequency (13.6%) when compared to a non-coal dust exposed population of 316 (1.0%). Those patients without rheumatoid factor showed an increase in HLA-A1 and B8 (58.6% and 51.7% respectively) when compared to the rheumatoid factor positive group (29.6% and 25.0% respectively). Clinical and radiological reassessment were performed on 49 of these patients who were also typed for HLA-DR antigens and properdin factor B allotypes. HLA-DR4 was raised in the rheumatoid factor positive group with rheumatoid arthritis (55.2% compared to 25.8% in the non-coal dust exposed group and 37.3% in coalworkers with normal radiographs). The HLA-DR results are comparable to those found in other studies of rheumatoid arthritis not associated with pneumoconiosis. The findings for HLA-A1, B8 and DR4, however, were not significant after correction was made for the number of antigens tested for. No particular Bf allotype was found to be associated with either the lung change or the arthritis. The induction of the pulmonary lesion in Caplan's syndrome is discussed in relation to the HLA findings.