Positive direct antiglobulin test in normal individuals. II

Area of Science:

• Immunology
• Hematology
• Transfusion Medicine

Background:

• The direct antiglobulin test (DAT) detects antibodies or complement bound to red blood cells (RBCs).
• Positive DAT can indicate autoimmune hemolytic anemia or other conditions, but can also be found in healthy individuals.
• Immunoglobulin G (IgG) is a major antibody class involved in RBC sensitization.

Purpose of the Study:

• To investigate the specific IgG subclasses and quantities present on RBCs of healthy blood donors with a positive DAT.
• To determine if there is a correlation between IgG levels and RBC sequestration in these individuals.

Main Methods:

• Analysis of IgG subclasses (IgG1, IgG2, IgG3, IgG4) on RBCs from 22 healthy blood donors with positive DAT.
• Quantification of IgG molecules per RBC using sensitive assays.
• Clinical assessment for signs of RBC sequestration.

Main Results:

• All positive DAT cases in healthy donors were associated with either IgG1 or IgG4 subclasses.
• The number of IgG molecules per RBC did not exceed 1000 in any of the studied individuals.
• A potential threshold for IgG1 molecules per RBC was suggested for cell sequestration.

Conclusions:

• Healthy individuals with positive DAT predominantly have IgG1 or IgG4 on their RBCs.
• RBC sequestration is likely dependent on the quantity of IgG1 bound to the RBC surface, suggesting a critical level for clearance.