Subclasses of IgG H chain expressed in the rheumatoid synovium

A complementary DNA (cDNA) library was constructed from a 72 year-old patient's synovium removed at surgery of the left knee replacement. The number of independent clones was found to be 1.1 x 10(6). Eighty-seven (0.3%) positive plaques were obtained from 30,000 plaques of this library using a genomic probe containing a constant region of IgG1. In these positive plaques, ten independent clones were purified and the subclasses were identified by DNA sequences near the "Hinge" region. Seven clones were identified as gamma 2, two clones as gamma 1 and one clone as gamma 4 respectively. Measurement of the serum IgG subclasses in this patient indicated increased IgG2. We conclude that some patients of rheumatoid arthritis exhibit an increased level of a unique IgG subclass.