Factors influencing platelet survival during antilymphocyte globulin treatment.

The antiplatelet effect of antilymphocyte globulin (ALG) was studied during 49 courses of therapy of 4-5 d given to 43 patients with severe aplastic anaemia. Concomitant corticosteroid therapy was usually given in moderate ( MDC ) dosages from 10 to 30 mg daily (40 courses); in nine courses the ALG infusions were combined with high dose (20 mg/kg) methylprednisolone (HDC). Clinical side effects were mainly seen during the first ALG infusion. In all MDC -treated patients a decrease of the peripheral-blood leucocyte count to 20-30% of the pretreatment level during the first ALG infusion was associated with a severely shortened platelet survival. During subsequent infusions, which were tolerated much better, the survival of transfused platelets increased considerably. In the HDC-treated patients platelet survival was only slightly shortened on the first day of therapy, but the decrease of the leucocyte count was also less in these patients. Diffuse intravascular coagulation, circulating immune complexes and complement activation were excluded as major causes of the shortened platelet survival. Although ALG reacted with platelets in vitro and in vivo (as detected with indirect immunofluorescence), bystander destruction was likely during the first ALG infusion when massive leucocyte destruction occurred.