[PMC free content] [PubMed] [Google Scholar] 44. of monoclonal antiChen egg lysozyme (HEL) antibody, or in combination individually, HOD antigen amounts and anti-HOD antibody development were examined. Outcomes: Our outcomes demonstrate that anti-HEL antibodies independently or in mixture Rucaparib (Camsylate) suppressed anti- HOD IgM, which correlated with the speed of detectable reduction in HEL on HOD RBCs. Furthermore, contact with anti-HEL antibodies by itself or in mixture suppressed anti-HOD IgG development equally. Unexpectedly, mixture or specific anti-HEL antibodies induced AMIS and antigen modulation within an FcR-independent way. Pre-exposure of HOD RBCs to anti-HEL antibodies decreased antigen amounts and suppressed anti-HOD antibody development pursuing HOD RBC exposure. CONCLUSION: These results suggest that antibody-mediated antigen modulation may reflect a mechanism of AMIS that can occur independent of activating FcRs and may provide a surrogate to identify antibodies capable of inducing AMIS against different RBC antigens. Antibodies to distinct red blood cell (RBC) antigens that develop following transfusion or pregnancy can lead to hemolytic disease of the fetus and newborn.1C4 Currently, the only commercially available prophylaxis that can actively prevent anti-RBC antibody development following antigen exposure is Rh immune globulin (RhIg).5C10 RhIg, polyclonal anti-RhD generated from pooled donor serum administered to prevent de novo anti-D development, is the most commonly employed example of antibody-mediated immunosuppression (AMIS). As the availability of RhIg donors is limited and the only available immunoprophylaxis is against RhD, there is a critical need to develop monoclonal antibody alternatives to RhIg and immunoprophylaxis to other RBC antigens. As different monoclonal antibodies to the RhD antigen can have differential immunological outcomes,11C20 understanding the mechanism regarding how monoclonal antibodies induce AMIS can facilitate the development and accurate assessment of monoclonal antibodies against RhD and other RBC antigens. While the mechanisms responsible for RhIg-induced AMIS remain unknown, several hypotheses have been suggested, including rapid clearance and/or steric hindrance of RhD+ RBCs to prevent B-cell recognition or direct immune modulation.21C23 However, as RBC clearance rates do not necessarily correspond to the ability of an Rucaparib (Camsylate) antibody to induce AMIS23 and several studies suggest that steric hindrance or inhibition of the immune response through inhibitory Fc receptors (FcRs) may not play a role in AMIS,24C28 alternative mechanisms may be responsible. Recent studies using the KEL model system demonstrate that AMIS to the KEL RBC antigen correlates with antigen modulation,29,30 a phenomenon referring to antibody-induced loss of the target RBC antigen. In this setting, anti-KEL antibodies induce complement fixation and subsequent antigen modulation, which was found to be dependent on both complement and activating FcRs.31C36 Similarly, previous studies demonstrate that FcRs are also required for anti-HEL (hen egg lysozyme) antibodyCinduced antigen loss following engagement of the HEL antigen expressed in a membrane-bound form on RBCs (mHEL RBCs).36 However, when Sema6d HEL is expressed along with ovalbumin and human Duffy as a fusion protein on RBCs (HOD RBCs), AMIS to HOD occurs independent of FcRs,28 suggesting that anti-HELCinduced AMIS following HOD RBC exposure may occur Rucaparib (Camsylate) independent of antigen modulation. These collective data suggest that while antigen modulation may mediate anti-KELCinduced AMIS, anti-HEL antibodies likely induce AMIS to the HOD antigen through an alternative mechanism. Furthermore, while previous studies have separately examined monoclonal antibodyC mediated AMIS to the HOD alloantigen and the role of FcRs in antigen modulation of HEL on mHEL RBCs,27,36,37 no studies have formally examined whether monoclonal anti-HELs antibodies mediate antigen modulation to the HOD antigen. Therefore, we sought to determine whether AMIS to HOD RBCs occurs via monoclonal antibodyCinduced antigen modulation. To study this, we used the previously established HOD RBC model to define the impact of potential changes in surface RBC antigen as a mechanism responsible for AMIS.27,28,38,39 Our results demonstrate that monoclonal anti-HEL antibodies individually or in combination inhibit the downstream antibody response to HOD RBCs, in support of previous findings.27 Anti-HELCinduced AMIS not only correlated with a decrease in the level of detectable HEL antigen on the RBC surface, but both antigen modulation and AMIS occurred independent of activating FcR function. Together, these data suggest that monoclonal antibodies may inhibit antibody responses to some RBC antigens through FcR-independent modulation of the target antigen. MATERIALS AND METHODS Mice.