Question

The cell-mediated immunity inside the human body is carried out by
A. T lymphocytes.
B. B lymphocytes.
C. Thrombocytes.
D. Erythrocytes.

Answer 1

Hint: Immunity is of two types, viz. innate immunity and acquired immunity. Acquired immunity can be either humoral or cell-mediated, based on the participation of B and T lymphocytes respectively. The cell-mediated immunity inside the human body is carried out by the cells that mature in the thymus.

Complete answer: The cell-mediated immunity is a part of acquired immunity. It involves the activation of phagocytes and antigen-specific T-lymphocytes. These cells release various cytokines in response to an antigen, rather antibodies. T-lymphocytes undergo a selection process in the thymus gland, i.e. it becomes mature in the thymus gland. They originate in the haematopoietic stem cells like other blood cells and these cells have their own receptors known as T-cell receptors. They move in the lymphatic system and get activated once it encounters pathogens.
a) Antibodies are made up of a particular cell type called B-lymphocytes. Macromolecules present in extracellular fluids, such as antibodies, mediate humoral immunity. Activation of antigen-specific T-lymphocytes triggers cell-mediated immunity. It is an immune response that does not require antibodies.
b) Thrombocytes are tiny cells in the form of a disc that is found in the blood and spleen. Actually, these are fragments of very large cells called megakaryocytes in the bone marrow. To slow or stop bleeding and for wound healing purposes, they help form blood clots.
c) Erythrocytes are also called red blood cells (RBCs). They are biconcave cells that can transport oxygen and carbon dioxide between the lungs and tissues. These cells are filled with iron-containing haemoglobin.
So, the correct answer is option A.

Note: After an initial response to a particular type of pathogen, acquired immunity produces an immunological memory which contributes to an improved response when encountering the pathogen later. Both humoral immunity and cell-mediated immunity are included in the acquired immune system.