Correct option is D
Explanation-
Option d - Both IgG F(ab')₂ fragment and J chain
This is because J chain is unique to IgM → strong recognition. IgG F(ab')₂ shares regions with IgM → possible cross-reaction in Western blotting due to structural similarity. Mouse IgM contains both F(ab')₂ fragments and a J chain. Antibodies produced in the rabbit could recognize epitopes on both of these components. Therefore, the rabbit antiserum could potentially recognize both in a Western blot.
Incorrect options-
Option a: IgG F(ab')₂ fragment only
The rabbit was immunized with mouse IgM, not IgG. The F(ab')₂ region of IgG and IgM are different in their amino acid sequences and epitopes. So, antibodies raised against IgM are unlikely to recognize IgG F(ab')₂ fragments. There is no guarantee of cross-reactivity between IgM and IgG fragments.
Option b: J chain only
While the J chain is present in IgM, it is only one part of the molecule. The question asks which components could be recognized, not just one. Since the rabbit was exposed to whole IgM, the antiserum would likely contain antibodies against multiple regions, not only the J chain.
Thus, selecting only the J chain is too narrow an answer.
Option c : IgG Fc fragment only
Again, the rabbit was immunized with IgM, not IgG. The Fc region is class-specific, meaning IgG and IgM have different Fc regions. Therefore, antiserum against IgM will not recognize the Fc portion of IgG.
So, the correct answer is option d - Both IgG F(ab')₂ fragment and J chain.
