A proposed mechanism of action for ALG and ATG in severe acquired aplastic anaemia.

In this study we have shown that various batches of anti-lymphocyte globulin (ALG), anti-thymocyte globulin (ATG) and human intravenous immunoglobulin (IV Ig) all contain antibodies with the capacity to block lymphocyte receptors for the Fc region of IgG, i.e., Fc gamma receptors. These antibodies may exert an effect on Fc gamma receptor bearing suppressor T cell function in vivo. Since T cells have been implicated in the pathogenesis of acquired severe aplastic anaemia, it is conceivable that administration of Fc gamma receptor blocking antibodies in the form of ALG, ATG or IV Ig preparations may be important in the treatment of the disease. The level of Fc gamma receptor blocking produced by these IgG preparations was however found to vary from batch to batch and one lymphocyte donor to another. In vivo Fc gamma receptor modulation will therefore only occur when the "correct" batch of IgG is used, thus affording a possible explanation for the variable clinical response of patients to this type of therapy.