Question

Match the antibody in Column I with the appropriate description in Column II:

$\begin{array}{cccc}& ColumnI& & ColumnII\\ 1.& lgA& a.& Maximumantigenbindingcapacity\\ 2.& lgD& b.& Predominantimmunoglobulininbodilysecretions\\ 3.& lgE& c.& Physiologicalroleunknown\\ 4.& lgG& d.& Mediatesallergicresponse\\ 5.& lgM& e.& Mediatesopsonisation,cancrossplacenta\end{array}$

• A. 1 - b, 2 - c, 3 - d, 4 - e, 5 - a
• B. 1 - e, 2 - c, 3 - d, 4 - b, 5 - a
• C. 1 - d, 2 - c, 3 - a, 4 - b, 5 - e
• D. 1 - c, 2 - d, 3 - a, 4 - b, 5 - e

Answer 1

The correct option is A

1 - b, 2 - c, 3 - d, 4 - e, 5 - a

There are 5 classes of antibodies IgG, IgM, IgA, IgD and IgE. IgG is primary antibody produced by B cells. IgG mediates the phagocytosis of pathogens by binding to the receptors present on phagocytic cells with their Fc region. Thus the antibody enables phagocytic cells to recognise pathogens and mediates their phagocytosis in a process called opsonisation. IgM is secreted as a pentamer i.e., five monomers joined by disulfide bonds. Each monomer has two antigen binding sites. As IgM is a pentamer, it has 10 antigen binding sites, which is the maximum among the immunoglobulins. IgA is the predominant antibody found in bodily secretions like saliva, tears etc., and is secreted as a dimer. IgE mediates allergic reactions by binding to mast cells and basophils. IgD constitutes merely 0.2% of the serum and its physiological role is still unknown.