IgA rheumatoid factor in the sera and saliva of patients with rheumatoid arthritis and Sjögren's syndrome

With a sensitive radioimmunoassay we have found elevated IgA rheumatoid factor (IgA-RF) levels in the sera of patients with rheumatoid arthritis, Sjögren's syndrome, and systemic lupus erythematosus. The IgA--RF showed a pattern of reaction with human IgG subclasses and animal gammaglobulins similar to that of IgM-RF from the same patients. Rheumatoid factors of both classes were shown to be present in saliva of patients with rheumatoid arthritis and Sjögren's syndrome.