Subclasses of IgG produced in the rheumatoid synovium.

The subclass distribution of IgG plasma cells was studied in sections of rheumatoid synovial tissue from 15 cases with seropositive rheumatoid arthritis and 8 cases with various types of seronegative arthritis, using the immunofluorescence technique and monoclonal IgG-subclass-specific antibodies. In most tissues, plasma cells of all the four subclasses were present, and IgG1 was usually the dominating subclass. The frequency of IgG3 plasma cells was usually higher than that of IgG2. The results are partly in contrast with previous observations and do not give evidence for a subclass-specific polyclonal B-cell activator, growth factor or differentiation factor.