In Rh isoimmunisation, the critical window for anti-D immunoglobulin administration is within 72 hours of a sensitising event. In a Rh-negative woman at 28 weeks of gestation with no anti-D antibodies, antenatal prophylaxis is recommended. What is the mechanism by which anti-D immunoglobulin prevents Rh sensitisation?

• A Anti-D stimulates maternal T-regulatory cells to suppress the immune response to Rh D antigen
• B Anti-D binds to D antigen on fetal red cells that have entered maternal circulation, opsonising them for rapid splenic clearance before they can induce a primary immune response ✓
• C Anti-D directly neutralises maternal anti-D antibodies already formed
• D Anti-D binds to maternal B lymphocytes expressing D antigen receptors, preventing clonal expansion

Explanation

Anti-D immunoglobulin prevents Rh sensitisation through the mechanism of 'antibody-mediated immune suppression' (AMIS) — the exogenously administered anti-D IgG binds to the D antigen on fetal RBCs that have entered maternal circulation via fetomaternal haemorrhage, coating them for rapid opsonisation and phagocytosis by macrophages in the spleen before they can be processed by maternal B lymphocytes to initiate a primary anti-D immune response. The exact additional mechanisms may include direct signalling suppression of B cell activation (epitope masking). This prevents primary sensitisation; it cannot reverse sensitisation that has already occurred.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.