Dr. Jatin Mehta (NII, Delhi)

Question asked in Section - C of  CSIR-NET December 2014.
Our endeavor here at grassroots academy is to make erudite scholars out of students and to fulfill this vision; we want to make the teaching a very interactive activity so as to inculcate scientific thinking and to forge a tradition par excellence!

Here are some questions asked in CSIR-NET December 2014, along with their answers.

Q. 93.  A technician wanted to make rabbit antiserum specific for mouse IgG. The technician injected rabbit with purified mouse IgG but obtained antiserum which reacted strongly with each of the other mouse isotopes. Which of the procedures mentioned below will allow him to make antiserum specific for IgG only?
1.  Injecting rabbit with purified F (ab)2’ region of the IgG antibody.
2.  Injecting rabbit with purified heavy chain of the IgG  antibody.
3.  Injecting rabbit with purified light chain of the IgG antibody.
4. Injecting rabbit with purified F(ab)’ region of the IgG antibody.

Ans 93. Antibodies which are specific for Mouse IgG should recognize the heavy chain of mouse IgG. The heavy chain is the most conserved among the antibodies and it is also known as the isotypic determinant which also coincide with the Fc fragment of an antibody.
Therefore, the answer is (2)- injecting rabbit with purified heavy chain of IgG antibody.
Remember, that antibodies can't be raised against the F(ab) fragment as they constitute the light chain and light chain or the idiotypic determinant differ between 2 antibodies of the same subtype.

Q.94. In order to precipitate a particular protein by its specific antiserum, it was found that the protein formed cross- linked lattice with specific polyclonal antiserum but failed to precipitate with specific monoclonal antiserum. Which of the following would accurately justify the reason for this behavior?
1.  The protein has multiple has multiple copies of the same epitope specific for the monoclonal antibody.
2.  The protein has multiple distinct epitopes but each has a single copy.
3.  There is total absence of epitopes in the protein.
4.  The protein has multiple copies of different epitopes.

 Ans 94. If a protein is precipitated by either a polyclonal serum or there are multiple copies of the same epitope specific for the monoclonal antibody, then there will be a lattice formed as shown below.

 Whereas in case of a monoclonal antibody having a single epitope, the following structure would be formed.

If you see in the above structure there is no lattice formed like the earlier one and hence the chances of precipitation are quite low.
There the correct answer is choice (2)-  The protein has multiple distinct epitopes but each has a single copy.

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