Rh(D) Immunoglobulin: Mechanism of Action

Passive Immunization

Rh(D) immunoglobulin (RhIG) is a sterile solution containing concentrated anti-Rh(D) antibodies derived from pooled human plasma. Its primary function is to provide passive immunization against Rh(D) antigen, preventing the development of Rh(D) alloimmunization in Rh(D)-negative individuals.

Mechanism of Action

RhIG works by binding to and inactivating any fetal Rh(D)-positive red blood cells that may have entered the maternal circulation. This binding prevents the maternal immune system from recognizing the Rh(D) antigen as foreign, thus preventing the initiation of an immune response and the subsequent production of anti-Rh(D) antibodies.

Target Cells

The target cells for RhIG are fetal Rh(D)-positive red blood cells. These cells can cross the placental barrier during pregnancy, particularly during delivery, trauma, or invasive procedures. The anti-Rh(D) antibodies in RhIG effectively neutralize these cells before they can stimulate an immune response.

Antibody Isotype

The predominant antibody isotype in RhIG is IgG, specifically IgG1 and IgG3 subclasses. These isotypes are capable of crossing the placenta, allowing the administered antibodies to reach and neutralize fetal red blood cells in the maternal circulation before they can initiate an immune response. The relatively high concentration of IgG antibodies is crucial for the efficacy of the treatment.

Clinical Applications

RhIG is primarily used in Rh(D)-negative pregnant women to prevent Rh(D) alloimmunization and hemolytic disease of the newborn (HDN). Prophylactic administration is typically given at specific times during pregnancy and postpartum.

Pharmacokinetics and Elimination

After administration, RhIG is catabolized and eliminated from the maternal circulation over several weeks. The half-life of the immunoglobulin is such that protection against sensitization remains effective for a sufficient duration.

Adverse Effects

Adverse effects are generally rare and mild, and include injection site reactions such as pain, redness, or swelling. More serious reactions are extremely uncommon.