In vitro production of platelet-binding IgG in childhood idiopathic thrombocytopenic purpura.

We studied two boys, 9 and 10 years old, respectively, who underwent splenectomy eight months and six weeks after initially presenting as "typical" cases of childhood ITP. Splenic leukocytes from each child were cultured and net synthesis rates of IgG determined. Splenic synthesis rates of IgG were five-and sevenfold greater, respectively, than in spleens of control subjects. A significant portion of the splenic culture-produced IgG from each patient demonstrated specificity for homologous and autologous platelets. Synthesis rates of IgG were determined on serial cultures of bone marrow cells from the 10-year-old boy who failed to respond to splenectomy. His initial marrow synthesis rate of IgG was five times greater than mean control values. His synthesis rate of IgG in marrow decreased to the control range in association with immunosuppressive therapy and intesive platelet transfusions. These data suggest that (1) the spleen was a production site of platelet-binding IgG in the two children, and (2) the bone marrow may have been an additional site of production in our second patient.