Systemic lupus erythematosus (SLE) is characterized by overactive B cells that differentiate into autoantibody-forming cells, aberrant T cell function that provides helping B cells produce autoantibodies, and overproduction of proinflammatory cytokines. However, immunodysregulation in lupus pathogenensis remains incomplete. We examined mitogen-stimulated production of proinflammatory cytokines, cell proliferation, T cell activation, and T cell apoptosis in vitro in pristane-induced lupus BALB/c mice compared to normal mice. LPS-stimulated production of IL-6 and IL-10 by splenocytes and macrophages from pristane-induced lupus mice were remarkably up-regulated compared to normal mice, whereas production of macrophage TNF-${alpha}$ was significantly down-regulated. Moreover, in vitro production of IL-2, IL-6, IL-10 and IFN-${gamma}$ by Con A-stimulated splenocytes, cell proliferation in LPS- or Con A-stimulated- thymocytes and splenocytes, and expression of CD69+CD4+ T cells in Con A-stimulated splenocytes were greatly increased in cells derived from pristane-induced lupus mice compared to normal mice. in addition, splenic T cells and CD4+ T cells in thymocytes from pristane-induced lupus mice were more resistant than nonautoimmune normal cells to Con A-induced apoptosis. Our findings indicate that immuroregulatory abnormalities of T cells and hyperreactivity of B cells in the in vitro immune responses in pristane-induced lupus mice may explain some of lupus pathogenesis.