Variation of anti‐Fas antibodies in different lots of intravenous immunoglobulin

BACKGROUND AND OBJECTIVES: Previous studies have presented evidence that human immunoglobulin G preparations for intravenous use contain antibodies directed against the death receptor Fas (CD95). The function of these antibodies was described as either antagonistic or agonistic; therefore, inhibiting or stimulating Fas-dependent apoptosis. Based on these reports, we asked whether the proportion of antagonistic and agonistic anti-Fas activities differs between different lots of intravenous immunoglobulin (IVIG). Variations between lots would open the possibility to preselect suitable lots of IVIG for different therapeutic purposes. MATERIALS AND METHODS: Eleven lots of IVIG were tested for their ability to induce or inhibit Fas-dependent apoptosis. The biological significance of anti-Fas antibodies was confirmed by including anti-Fas antibodies purified from IVIG and IVIG depleted of anti-Fas antibodies in the study. RESULTS: All 11 lots inhibited FasL-induced apoptosis. In addition, five lots stimulated apoptosis in the absence of FasL. Depletion of anti-Fas antibodies from IVIG abolished the capacity of IVIG to inhibit FasL-induced apoptosis, but reduced the ability to induce apoptosis only slightly. CONCLUSION: The inhibition of FasL-induced apoptosis by IVIG is because of the presence of antagonistic anti-Fas antibodies. The activity of these antibodies differs considerably between different lots. On the other hand, the induction of apoptosis by IVIG is probably because of the concerted action of a range of different antibodies. The variation in the proportion of stimulating and inhibiting anti-Fas activities between different lots of IVIG opens the possibility to preselect suitable lots for different therapeutic purposes.