Antibody-mediated immune suppression (AMIS)-inducing antibodies trigger in vivo RBC antigen and membrane loss independent of clearance
AMIS-inducing antibodies including anti-D trigger in vitro RBC antigen loss and membrane transfer to macrophages through trogocytosis
Red blood cell (RBC) alloimmunization to paternal antigens during pregnancy can cause hemolytic disease of the fetus and newborn (HDFN). This severe and potentially fatal neonatal disorder can be prevented by the administration of polyclonal anti-D through a mechanism referred to as antibody-mediated immune suppression (AMIS). Although anti-D prophylaxis effectively prevents HDFN, a lack of mechanistic clarity has hampered its replacement with recombinant agents. The major theories behind AMIS induction in the hematological literature have classically centered around RBC clearance, however antigen modulation/loss has recently been proposed as a potential mechanism of AMIS. To explore primary mechanisms of AMIS, we studied the ability of eleven different antibodies to induce AMIS, RBC clearance, antigen-loss, and RBC membrane loss in the HOD (Hen egg lysozyme-Ovalbumin-human Duffy) murine model. Antibodies targeting different portions of the HOD molecule could induce AMIS independent of their ability to clear RBCs; however, all antibodies capable of inducing a strong AMIS effect also caused significant in vivo loss of the HOD-antigen in conjunction with RBC membrane loss. In vitro studies of AMIS-inducing antibodies demonstrated simultaneous RBC antigen and membrane loss, which was mediated by macrophages. Confocal live cell microscopy revealed that AMIS-inducing antibodies triggered RBC membrane transfer to macrophages consistent with trogocytosis. Furthermore, anti-D itself can induce trogocytosis even at low concentrations, where phagocytosis is minimal or absent. In view of these findings, we propose trogocytosis as a mechanism of AMIS induction.