Immunology

(a) - Humoral immune response: This response involves the production of antibodies by B cells to neutralize pathogens and prevent infections. It is primarily mediated by the action of antibodies in bodily fluids.
- Cell-mediated immune response: This response is carried out by T cells, particularly cytotoxic T cells, which target and destroy infected cells or cancerous cells. It does not involve antibodies.
(b)

- An antibody molecule has a “Y” shaped structure with two heavy chains and two light chains.
- Variable region: Located at the tips of the Y, it binds to the antigen.
- Constant region: The stem of the Y, which determines the class of antibody (IgG, IgM, etc.).
- Hinge region: Located between the arms of the Y, allows flexibility.
- Disulfide bonds: Hold the heavy and light chains together.

Antibody-mediated immunity is also called the humoral immune response because the antibodies produced by B cells circulate in the body fluids (or humors) such as blood and lymph. The term “humoral” is derived from the Latin word humor, meaning fluid. Since this immune response occurs via soluble molecules in fluids and not through direct cell contact, it is termed the humoral response.

The two types of specialised cells which carry out the primary and secondary immune response:
1. B-cells (B lymphocytes): These cells are responsible for the production of antibodies during both the primary and secondary immune responses. The primary response occurs when the body encounters the pathogen for the first time, and the secondary response occurs during subsequent encounters with the same pathogen.
2. T-cells (T lymphocytes): These cells assist in the immune response by either helping B-cells produce antibodies (Helper T-cells) or directly killing infected cells (Cytotoxic T-cells).