In population samples in England and Wales a greater frequency of positive sheep cell agglutination tests has been found in Leigh and the Rhondda than in Wensleydale, the Vale of Glamorgan or Watford.
The urban population of Leigh had more X-ray evidence of lung pathology than the rural population of Wensleydale. Seropositive persons in both the urban populations of Leigh and the Rhondda and the rural populations of Wensleydale and Glamorgan had more X-ray evidence of lung pathology than seronegative individuals, the difference being significant for healed tuberculosis of the lungs, thickened basal pleura and increased basal vascular markings. The association between the first two and rheumatoid factor was equally present in those with and without arthritis but in the third it was limited to those with arthritis. A history of bronchitis was no more common in persons with a positive sheep cell test than in those with a negative test and the indirect maximum breathing capacity showed no significant relationship to rheumatoid factor titre.
No association was found between cigarette smoking and the sheep cell titre.
It is concluded that parenchymal lung and pleural disease may act as a stimulus to the production of rheumatoid serum factor and that this stimulus is independent of the presence or absence of arthritis.