Ficin-Treated Red Cells and Anti-M Reactivity
Ficin-treated red cells can be expected to demonstrate a negative reaction with patient serum containing anti-M.
Mechanism of Ficin Treatment on Red Blood Cells
Ficin is a proteolytic enzyme used in immunohematology to modify red blood cell membranes and enhance or destroy certain antigen-antibody reactions. When red blood cells are treated with ficin:
- The enzyme cleaves portions of the red cell membrane glycoproteins
- This modification affects different blood group antigens in specific ways
- Some antigens become more accessible (enhanced reactivity)
- Other antigens are destroyed (eliminated reactivity)
Effect of Ficin on MNS Blood Group System
Ficin treatment specifically affects the MNS blood group system in the following ways:
- Ficin destroys M and N antigens on the red cell surface by cleaving the sialoglycoprotein that carries these antigens 1
- The enzyme treatment removes the portion of the glycoprotein that contains the M and N determinants
- This destruction of M antigens eliminates the binding sites for anti-M antibodies
Interpretation of the Case
In this case:
- The patient's serum contains anti-M antibodies
- Untreated cells showed 2+ reactivity at immediate spin and 1+ at 37°C
- No reactivity was observed in the Coombs phase
- When these cells are treated with ficin, the M antigens are destroyed
- Without M antigens present, anti-M antibodies have no target for binding
Clinical Significance
Understanding the effect of enzyme treatment on blood group antigens is important for:
- Antibody identification in complex cases
- Differentiating between multiple antibodies
- Enhancing detection of weak antibodies 2
- Determining the clinical significance of antibodies
Ficin is known to enhance reactivity of antibodies in the ABO, Rh, Kidd, Lewis, I, and P blood group systems while destroying reactivity of antibodies in the Duffy and MNS blood group systems 1, 2.
Practical Applications
In blood bank laboratories:
- Ficin treatment helps identify clinically significant alloantibodies that may be masked by other reactions
- It's particularly useful when working with antibodies of undetermined specificity
- The pattern of reactivity with enzyme-treated cells provides valuable information about antibody specificity
- For anti-M specifically, the loss of reactivity with ficin-treated cells is a characteristic finding that helps confirm its identity
Therefore, the correct answer is B: Negative.