Monocyte monolayer assay

The monocyte monolayer assay (MMA) is used to determine the clinical significance of alloantibodies produced by blood transfusion recipients.

[1] The assay is used to assess the potential for intravascular hemolysis when incompatible cellular blood products are transfused to the anemic patient.

Specific white blood cells, called monocytes, are tasked with ingesting foreign material and become activated during certain inflammatory events.

[11] With some exceptions, many non-ABO blood group system antigens require a sensitizing event to stimulate antibody production.

[4] The clinical significance of an alloantibody depends on its ability to cause a decrease in donor red blood cell survival.

[12] Characteristics of clinically significant alloantibodies include: immunoglobulin G antibody subclass, reactivity at body temperature, and ability to cause red blood cell agglutination in the presence of anti-human globulin (AHG) in an indirect antiglobulin test.

Criteria for a positive MMA will vary by laboratory, though the originally established threshold set by Sandra Nance et al., is >20% phagocytic activity observed.

The image on the left shows a monocyte actively phagocytizing an antibody-sensitized red blood cell. The image on the right shows multiple RBC that have been phagocytized by a single monocyte.