A 28-year-old primigravid woman comes to the office for a routine prenatal checkup at 28 weeks gestation. The patient has no concerns and has had an uneventful pregnancy to date. Physical examination shows a uterine size concordant with ultrasound dates, and fetal cardiac activity is in the normal range. After reviewing the results of her laboratory evaluations, the physician administers an injection of anti-Rh(D) immunoglobulin. The administered antibodies most likely belong to which of the following immunoglobulin classes?

Question

A 28-year-old primigravid woman comes to the office for a routine prenatal checkup at 28 weeks gestation.  The patient has no concerns and has had an uneventful pregnancy to date.  Physical examination shows a uterine size concordant with ultrasound dates, and fetal cardiac activity is in the normal range.  After reviewing the results of her laboratory evaluations, the physician administers an injection of anti-Rh(D) immunoglobulin.  The administered antibodies most likely belong to which of the following immunoglobulin classes?

Quizplus · Accepted Answer

11ec160b_37d0_e188_9249_5bf4d19da521_MD0001_00 Rhesus (Rh) antigens are a group of nonglycosylated, transmembrane proteins found on the surface of red blood cells. The D antigen is the most immunogenic of the group and is present on the erythrocytes of Rh-positive individuals. When an Rh-negative mother becomes pregnant with an Rh-positive fetus, fetal red blood cells can enter the maternal circulation and elicit a maternal antibody response with the formation of memory B lymphocytes (Rh alloimmunization). After Rh alloimmunization occurs, subsequent pregnancies with Rh-positive fetuses will be at risk for hemolytic disease of the newborn. To avoid maternal Rh alloimmunization, Rh-negative mothers must be prevented from mounting an immune response against the D antigen. Anti-Rh(D) immunoglobulin is a polyclonal antibody product consisting of IgG anti-D antibodies collected from pooled donor plasma. It is administered to Rh-negative women during gestation and in the immediate postpartum period. Once given, anti-Rh(D) antibodies bind to Rh-positive fetal erythrocytes that enter the maternal circulation, preventing their interaction with the maternal immune system by promoting sequestration and elimination in the mother's spleen (ie, the mononuclear phagocyte system). Although IgG antibodies can cross the placenta, anti-Rh(D) IgG antibodies do not cause significant transplacental fetal hemolysis because the amount of antibody administered is negligible compared with the amount produced in a typical immune hemolytic reaction. (Choice A) IgA is primarily a mucosal antibody. Patients with IgA deficiency can have an anaphylactic reaction during the administration of intravenous immunoglobulin. (Choice B) IgD is present in very low concentrations in the blood and is typically coexpressed with IgM as a B-cell membrane receptor. (Choice C) IgE plays a significant role in allergic responses and in the immune response to parasitic infections. (Choice E) Multivalent IgM antibodies are generally more effective than IgG antibodies at promoting agglutination of foreign antigens and activating complement, which would result in lysis of fetal erythrocytes in the maternal circulation. However, macrophages do not have receptors for IgM; therefore, anti-D IgM does not provide the same immunoprophylactic effect (eg, sequestration and clearance of Rh-positive erythrocytes) as anti-D IgG. Educational objective: Anti-Rh immunoglobulin consists of anti-D IgG antibodies that bind to Rh-positive fetal erythrocytes, promoting clearance by maternal reticuloendothelial macrophages and preventing maternal Rh sensitization. It is routinely administered to Rh-negative women during gestation and immediately postpartum. __________ References: Mechanisms of anti-D action in the prevention of hemolytic disease of the fetus and newborn. (http://www.ncbi.nlm.nih.gov/pubmed/20008198)

A 28-Year-Old Primigravid Woman Comes to the Office for a Routine