IVIG and HLA antibodies. Evidence for inhibition of complement activation but not for anti-idiotypic activity

The immediate effects of IVIG can be due to the presence of anti-idiotypic antibodies or inhibition of complement, but there is limited data about these possible mechanisms specifically on HLA antibodies (HLA Abs). Potential blocking activity of IVIG on HLA Ab binding and complement activation was investigated by flow cytometry. IVIG did not inhibit the IgG binding of any of 23 sera from sensitized patients containing Abs to several different HLA specificities. In contrast, IVIG produced significant dose-dependent complement inhibition. Low IVIG concentrations could be inhibitory if there was little C3 activation, but high concentrations were needed when C3 was activated more efficiently. The data do not support any significant contribution of anti-idiotypic antibodies against HLA Abs to the activity of IVIG. The results also highlight a relationship between the magnitude of C activation and the C inhibitory effect of IVIG.