Answer: IgA.
- A IgG
- B IgM
- C IgA
- D IgE
Correct answer: C. IgA
Explanation: IgA is the main antibody in secretions: saliva, breast milk (colostrum), tears, mucus. It protects body surfaces from pathogens before they enter the bloodstream. Secretory IgA (sIgA) exists as a dimer.
An antibody is Y-shaped, with two identical antigen-binding sites at the tips of the variable regions - each shaped to recognise one specific antigen - while the constant (Fc) region at the base is recognised by immune cells to trigger further responses.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.