Association of serum IgM kappa monoclonicity in patients with Sjögren's syndrome with an increased proportion of kappa positive plasma cells infiltrating the labial minor salivary glands.

Minor salivary gland biopsy specimens from 11 patients with primary Sjögren's syndrome with circulating monoclonal IgM kappa cryoglobulins, seven without cryoglobulins, and four patients with rheumatoid arthritis and Sjögren's syndrome (one with monoclonal and three with polyclonal cryoglobulins) were examined by the peroxidase antiperoxidase bridge technique, using antihuman kappa and lambda antibodies. In 6/11 patients with primary Sjögren's syndrome and in one patient with Sjögren's syndrome and rheumatoid arthritis with monoclonal cryoglobulins a predominance of plasma cells containing intracytoplasmic kappa light chains was found (kappa:lambda greater than 3:1). Two of those seven patients had immunohistological features of immunocytomas. In the other five patients with circulating monoclonal cryoglobulins the kappa:lambda ratio of positive cells did not exceed 3:1, while six out of seven patients without cryoglobulins and the patients with rheumatoid arthritis and Sjögren's syndrome with polyclonal cryoglobulins had almost equal numbers of kappa and lambda stained cells. One of seven patients with primary Sjögren's syndrome without cryoglobulins had an increased number of lambda light chain positive cells, indicating a non-secretory lambda monoclonal population. These findings suggest that the main area of B cell monoclonal expansion in primary Sjögren's syndrome may be the affected exocrine glands.