CD5-expressing B lymphocytes in the blood and salivary glands of patients with primary Sjögren's syndrome.

CD5, the human counterpart of Ly-1 molecules in the mouse, are detectable but weakly expressed on a minute fraction of circulating B cells. The number of CD5 + B cells in the blood of patients with Sjögren's syndrome was slightly higher than in control blood, but it became statistically significant after treatment of the cells with phorbol myristic acetate. These numbers were even higher in patients with homogeneous serum bands than in the others. A few scattered cells were stained with anti-human IgM antibody on salivary gland sections, and among them 5-10% were found to be positive for anti-CD5.