THE ROLE OF THE HUMORAL IMMUNE SYSTEM IN CHILDHOOD IDIOPATHIC THROMBOCYTOPENIC PURPURA (ITP)

The pathogenesis of childhood ITP is not well understood. To explore the role of the humoral immune system in ITP, bone marrow (BM) and splenic (Sp) lymphocytes from ITP and control children were cultured and in vitro IgG production was measured; in some cases platelet specificity was assessed. Platelet-associated IgG (PAIgG) was also determined as a measure of platelet-bound antibody or complexes. BM and Sp cells were cultured in 20% fetal calf serum, Dulbecco's medium, for 10 days. The Fab-anti-Fab immunoassay was used in all IgG determinations. Platelet specificity was determined using an IgG absorption technique. PAIgG of circulating platelets from control and ITP subjects was assayed directly after washing the platelets by gel filtration. Mean BM synthesis rates (ngIgG/106 lymphocytes/day) of acute and chronic ITP cases were 219±92 and 619±216; both were significantly greater than control values of 98±62 (p<0.01 and 0.001 respectively). SpIgG synthesis rates of chronic cases and controls were 85.9±52 and 22.9±11, respectively, and differed significantly (p< 0.001). Four of 4 splenic samples showed significant binding to target platelets which averaged 1232 ngIgG/109 platelets. Blood PAIgG values (ngIgG/10 platelets) of acute cases (range 5588–56,250) and chronic cases (range 2425–16,800) were greater than control values of 1089±213 (p<0.001) and the two ITP groups appeared to reflect different statistical populations. We conclude these data support immune-mediated platelet destruction in both acute and chronic childhood ITP. Differences in PAIgG values, although preliminary, may be of diagnostic importance and suggest different mechanisms may be involved.