Question

Damage to the thymus in a child may lead to
(a)Loss of cell-mediated immunity
(b)A reduction in the hemoglobin content in the blood
(c)A reduction in the number of plasma proteins
(d)Loss of antibody-mediated immunity

Answer 1

Hint: The thymus is a primary lymphoid organ that is responsible for the differentiation of immature lymphocytes into antigen-sensitive lymphocytes. Another such example of a primary lymphoid organ is the bone marrow which produces the lymphocytes.

Complete answer:
The thymus is a primary lymphoid organ that is lobed in structure and present near the heart and below the breastbone (sternum). Thymus along with the bone marrow provides a microenvironment for the growth and differentiation of the T-lymphocytes. The T-lymphocytes are responsible for the cell-mediated immune response (CMI). This immune response is responsible for the ability of the body to differentiate between ‘self’ and ‘non-self’, thus resulting in the rejection of grafts after transplantation. Thus, damage to the thymus in a child may lead to the loss of cell-mediated immunity as the T-lymphocytes will not be able to proliferate properly.

Additional Information:
 -Lymphocytes after maturation migrate to secondary lymphoid organs like the spleen, lymph nodes, tonsils, Peyer’s patches of the small intestine, and appendix.
-Secondary lymphoid organs are responsible for providing sites of interactions between lymphocytes and antigens.
-These organs filter out the blood and trap the antigens present in it, which causes the activation of the lymphocytes (immune response).
-Lymphoid tissue is present within the lining major tracts of the body such as respiratory, digestive, and urogenital tracts and is known as Mucosa-Associated Lymphoid Tissue (MALT).
So, the correct option is ‘Loss of cell-mediated immunity’.

Note: -The thymus is large in size at the time of birth but keeps decreasing in size with age and by the time puberty is reached, the thymus becomes very small.
-This is the reason why people who are in old age have a weakened immune system as their thymus is very diminished in size.
-Another type of immune response known as the antibody-mediated immune response is also present which is carried out by B-lymphocytes with the help of T-cells. It is also known as humoral immune response as the antibodies are present in the blood.