The British literature on Caplan's syndrome is
briefly reviewed with particular reference to the pathogenesis
of the pulmonary lesions and an investigation is described
which was designed to throw fresh light upon this.
Statistical analysis of the results revealed an
association between the levels of several serum protein
fractions am> the severity of the lung lesions independently
of the severity of arthritis. Elevation of α2- and
γ-globulins and reduction of albumin and of the albumin/
α2-globulin ratio are consistent with the tuberculous theory
of the aetiology of these lesions, but a trend was also
observed toward3 higher levels of ß-globulin with increasing
severity of pulronary lesions. Rheumatoid arthritis itself
rarely produces this effect and no increase of ß-globulin
has been reported in tuberculosis.
The previously observed association between the
presence of "Caplan lesions" in the lungs and positive
haemagglutination tests for rheumatoid arthritis was confirmed
and a significant correlation demonstrated between the agglutination titre and the ß-globulin level.
The literature on the nature of the rheumatoid factor
is reviewed and the conclusion reached that it exists naturally
as a 19s macroglobulin migrating electrophoretically as a
(ß2-globulin but that transformation to a 22s γ-globulin occurs
when serum is stored in the liquid state
Based on this conclusion and on the three-fold
relationship observed between the severity of "Caplan lesions",
the haemagglutination titre and the p-globulin level, a
hypothesis is proposed that the nodular pulmonary lesions
described by Caplan and perhaps some other lesions associated
with rheumatoid arthritis such as subcutaneous necrobiotic
nodules may be sites of synthesis of the rheumatoid factor.
It is further suggested that the raw material for this synthesis
may consist of ß-glycoprotein derived from the ground-substance
of degenerating collagenous tissue.
Observations consistent with this hypothesis are
quoted from the literature and several experiments are suggested
which, if done, might support or refute the hypothesis.