Flow cytometry analysis of the lymphoid populations from lymphoid tissues of diseased TRAF3/BCL2 double-tg mice, including spleen, nodes, blood, as well as ascites, and pleural effusion when found in the mice, showed that they were consistently composed by B cell expansions with distinct surface marker expression but all indicative of a mature B cell phenotype. The gene discussed is TRAF3; the disease is Pleural effusion.