CASP3 and autoimmune polyendocrinopathy: We found that APS IgG enhanced p38 MAPK phosphorylation significantly more than SLE/APS negative or HC IgG and that a p38 MAPK inhibitor (SB203580) reduced the increase in cleaved caspase-3 caused by APS IgG (Figure 4) This suggests that the enhanced pro-apoptotic effect of APS IgG is due to increased phosphorylation of the kinase p38 MAPK.