Quantitation of the Sm nuclear antigen in tissues and activated lymphocytes.

Anti-Sm antibodies are specific for the diagnosis of systemic lupus erythematosus both in humans and in mice. Because the autoantibody response to this nuclear ribonucleoprotein particle is probably antigen driven, we have quantitated the Sm antigen in cells and tissues, using a highly sensitive and specific enzyme-linked immunosorbent assay. The Sm content of several in vitro cell lines was determined to be approximately 1 pg of Sm/cell. We found that murine spleen cells stimulated in vitro with either T cell or B cell mitogens contained up to 10 times more Sm than did unstimulated cells and that they also released increased amounts of Sm. In a survey of organs from several mouse strains, we found that lymphoid tissues had the largest amounts of Sm and that the Sm content of a particular tissue correlated with its DNA content. Increased amounts of Sm in and around activated lymphocytes, as found in systemic lupus erythematosus, may provide a source of antigen for the induction of the anti-Sm autoantibody.