Question

In the Ouchterlony assay, we see a sharp precipitin arc form between antigen and antiserum. Why does this arc remain visible for a long time?

a) High antibody concentration
b) Low temperature
c) Slow diffusion rate
d) Insufficient antigen-antibody binding

Answer 1

The stability of the precipitin arc in the Ouchterlony assay results from the large size of the precipitin lattice, which is too big to diffuse through the gel matrix.

Step-by-step explanation:

In the Ouchterlony assay, a sharp precipitin arc forms between the antigen and antiserum, and this precipitin arc becomes visible at the zone of equivalence where there is an optimal ratio of antigen to antibody. The key reason for the stability and longevity of this precipitin arc is that the precipitin lattice is too large to diffuse through the gel matrix of the agar. Antigen-antibody interactions cause the formation of this lattice, which, once formed, is trapped in the gel and remains visible for a long time, hence acting as a reliable indicator in the assay.

Answer 2

The answer of the given statement that " this arc remain visible for a long time" is c) Slow diffusion rate

Explanation:

In the Ouchterlony assay, the formation of a sharp precipitin arc between antigen and antiserum is influenced by various factors. The key reason the arc remains visible for a long time is the slow diffusion rate.

During the assay, antigen and antibody diffuse through the gel medium at a rate that is influenced by factors like temperature and the concentration of agarose or agar in the gel. If the diffusion rate is slow, the antigen and antibody have more time to interact and form a distinct precipitin arc. This allows for a clear visualization of the reaction.

Options (a) High antibody concentration and (b) Low temperature may affect the intensity of the reaction, but they are not directly related to the longevity of the visible precipitin arc. Option (d) Insufficient antigen-antibody binding would likely result in a weaker or incomplete precipitin arc rather than influencing its duration.

Therefore, in the context of the Ouchterlony assay, the c) slow diffusion rate is the critical factor contributing to the prolonged visibility of the precipitin arc.