The critical mechanism by which Rh-D immunoprophylaxis (anti-D immunoglobulin) prevents maternal sensitization is:

• A Anti-D IgG blocks Rh-D antigen on fetal cells, preventing dendritic cell antigen presentation to naive T-helper cells
• B Anti-D IgG coats Rh-D positive fetal erythrocytes, causing rapid phagocytic clearance before B-cell recognition (passive antibody-mediated immune suppression) ✓
• C Anti-D activates complement, causing immediate intravascular hemolysis of fetal cells before splenic processing
• D Anti-D cross-links B cell FcγRIIB receptors, delivering an inhibitory signal and blocking B cell activation

Explanation

The dominant mechanism of Rh immunoprophylaxis by passive anti-D IgG is accelerated clearance of Rh-D positive erythrocytes via Fc receptor-mediated phagocytosis in the spleen and reticuloendothelial system, before B-lymphocytes can recognize the D antigen and mount a primary immune response. The antibody-coated cells are cleared too rapidly for T-cell-dependent B-cell activation and memory formation. Additional mechanisms include antigen masking and possible inhibitory signaling, but accelerated clearance is the primary mechanism. This is why the dose (300 μg = ~30 mL whole blood or 15 mL pRBC) is calculated based on the fetomaternal hemorrhage volume.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.