Question

How is adaptive immunity activated in our body?

Answer 1

Adaptive (acquired) immunity is the specific immunity acquired after birth. It is activated as follows:

1. Entry of the antigen: A pathogen or foreign antigen enters the body after crossing the non-specific defence mechanisms.
2. Processing and presentation: The antigen is captured and processed by antigen-presenting cells (macrophages, dendritic cells), which present its fragments on their surface along with HLA/self-marker molecules.
3. Activation of T-helper cells: T-helper cells recognise the presented antigen through their specific receptors and get activated.
4. Activation of B cells and T-cytotoxic cells: The activated T-helper cells then stimulate both B cells and T-cytotoxic cells.
5. Clonal selection and proliferation: The selected B and T cells divide repeatedly to give rise to a clone of cells, effector cells (plasma cells and cytotoxic T cells) and memory cells.
6. Effector action: B cells produce antibodies (humoral immunity) which neutralise the antigens; T-cytotoxic cells directly attack and kill the infected cells (cell-mediated immunity).
7. Memory: The memory cells remain in the lymph nodes for years and give a rapid secondary immune response on subsequent exposure.

Thus, adaptive immunity is activated by the specific recognition of the antigen by T and B lymphocytes, followed by their clonal expansion into effector and memory cells.