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.