Pure red cell aplasia: studies on an IgG serum inhibitor neutralizing erythropoietin.

A new type of IgG serum inhibitor in adult pure red cell aplasia (PRCA) has been investigated. This inhibitor is directed against circulating erythropoietin (Ep) (PRCA type B), rather than the erythroid marrow (PRCA type A). Thus, the IgG inhibitor, after interaction with Ep in solution, is precipitated together with Ep by addition of goat anti-human gamma-globulins. Pre-therapy PRCA serum, although apparently devoid of Ep, shows considerable Ep activity following acidification and boiling. The inhibitor is absent from post-therapy serum, while Ep levels are elevated. An experimental model for PRCA type B has been established in normal mice after prolonged administration of pre-remission serum IgG.