Which of the following enhances medium decrease the zeta potential, allowing antibody and antigen to come closer together?
a. Low ionic Strength solution (LISS)
b. Polyethylene glycol
c. Polybrene
d. Dithiothreitol – papain (ZZAP)
The correct answer and explanation is:
Correct Answer: a. Low Ionic Strength Solution (LISS)
Explanation (Approx. 300 words):
Zeta potential is the electrical potential at the boundary layer of red blood cells (RBCs). It creates a repulsive force that keeps RBCs from coming too close to each other. This repulsion can hinder the interaction between antigens on red blood cells and antibodies in serological tests.
Low Ionic Strength Solution (LISS) is used in immunohematology to enhance antibody-antigen reactions. It works by reducing the ionic strength of the surrounding medium, which lowers the zeta potential of red blood cells. When the zeta potential is reduced, the electrical barrier that normally keeps RBCs apart weakens. As a result, the distance between the cells decreases, and antibodies can more easily bridge between antigens on different cells, enhancing agglutination or sensitization.
LISS also accelerates the rate of antibody uptake by red blood cells, making it a common enhancement medium in antibody screening and identification procedures.
Here’s a quick look at the other choices:
- b. Polyethylene Glycol (PEG): PEG is an enhancement medium that removes water from the reaction environment, concentrating antibodies. It increases agglutination sensitivity but does not reduce zeta potential directly.
- c. Polybrene: A positively charged polymer that promotes RBC aggregation by neutralizing negative charges, but it’s more commonly used in viral studies or specialized testing, not as broadly as LISS in standard antibody detection.
- d. Dithiothreitol – papain (ZZAP): ZZAP is a combination of DTT (breaks disulfide bonds) and papain (an enzyme that cleaves protein structures), used primarily to treat red blood cells to remove bound antibodies—it doesn’t enhance agglutination by altering zeta potential.
In summary, LISS is specifically formulated to lower the zeta potential, thus allowing antibodies and antigens to come into closer proximity, making it the correct answer.