1

As I understand it, the anti-D will coat the fetal Rh+ RBCs, and since these have been marked by IgG, they will get phagocytosed among other things that will result in their destruction.

If the RBCs get phagocytosed, isn't there the possibility that the antigens produced in that phagocytosis get presented to lymphocytes, causing sensitization to the Rh antigen?

2

According to this 2006 review article:

In summary, the evidence indicates that prevention of RhD immunization by prophylactic anti‐D might occur both by rapid macrophage‐mediated clearance of anti‐D–coated RBCs and/or by down regulation of immature DCs or anti‐D–specific B cells before development of the anti‐D response occurs.

The author states that the macrophage-mediated clearance is most likely the predominant mechanism of prophaylactic anti-D's effects on maternal immune response. This is because "the flow of RBCs is predominantly through the red pulp (the site of destruction of IgG‐coated RBCs) and few RBCs enter the white pulp (areas of immune response generation)".

These [macrophage IgG Fc] receptors recognize cell‐bound IgG “labeling” target cells to which immunity has developed, mediating their accelerated phagocytosis and destruction. This is a noninflammatory process, avoiding unnecessary collateral tissue damage. Immune responses to blood‐borne antigens take place in the white pulp.

In other words, rapid clearance of anti‐D–coated RBCs by splenic macrophages in red pulp is non-inflammatory and will prevent a maternal (B-cell) immune response to RhD antigen.

Source:

  • Kumpel BM. On the immunologic basis of Rh immune globulin (anti‐D) prophylaxis. Transfusion 2006;46:1271‐1275.

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