Question

Name the major cells of the immune system. Give a detailed account of their response to an antigen attack in humans.

Answer 1

The major cells of the immune system are lymphocytes (T-cells and B-cells) and macrophages.

Response to an antigen attack:

1. T-cells: They mature in the thymus and are involved in cellular immunity. When a specific antigen is detected, T-cells transform into activated forms:
   1. Cytotoxic T-cells directly destroy infected cells by releasing lysosomal enzymes.
   2. Helper T-cells stimulate B-cells to produce antibodies and secrete lymphokines that enhance macrophage activity.
   3. Suppressor T-cells regulate the immune response to prevent overactivity. Some T-cells become memory cells for faster response upon future exposure.
2. B-cells: They mature in the bone marrow and are responsible for humoral immunity. Upon encountering antigens (often presented by macrophages), B-cells transform into plasma cells that secrete specific antibodies. These antibodies neutralize antigens or mark them for destruction by other immune cells. Some B-cells also become memory cells.
3. Macrophages: They act as antigen-presenting cells by engulfing pathogens and displaying their antigens, thus activating lymphocytes. They also destroy microbes by phagocytosis.