Question

Immunity in our body is of two types: (i) Innate immunity and (ii) acquired immunity. Innate immunity is a non-specific defence mechanism, whereas acquired immunity is pathogen-specific; it is called specific immunity too. Acquired immunity is characterised by memory. Antibodies are specific to antigens and there are different types of antibodies produced in our body: they are IgA, IgE, IgG and IgM. It shows primary response when it encounters the pathogen for the first time and secondary response during the subsequent encounters with the same Antigen/Pathogen.
(a) Name the two types of specialised cells which carry out the primary and secondary immune response. 
(b) Why is the antibody-mediated immunity also called as humoral immune response? 
Attempt either sub-part (c) or (d): 
(c) The organ transplants are often rejected if taken from suitable compatible persons. 
(i) Mention the characteristic of our immune system that is responsible for the graft rejection. 
(ii) Name the type of immune response and the cell involved in it. 
OR 
(d) How is active immunity different from passive immunity?

Hint:

Humoral immunity targets extracellular pathogens via antibodies, while cell-mediated immunity, involving T-cells, is crucial for rejecting grafts and fighting intracellular pathogens.

Answer 1

Step 1: For (a), the two types of specialized cells that carry out the primary and secondary immune responses are B-lymphocytes (B-cells), which produce antibodies, and T-lymphocytes (T-cells), which assist in coordinating the immune response and forming memory cells for faster secondary responses.
Step 2: For (b), antibody-mediated immunity is called humoral immunity because it involves antibodies produced by B-cells, which are dissolved in body fluids (historically called "humors") like blood and lymph, targeting extracellular pathogens.
Sub-part (c):
Step 3: For (c)(i), the characteristic of the immune system responsible for graft rejection is its ability to recognize foreign antigens, specifically the major histocompatibility complex (MHC) molecules on the donor organ, as non-self.
Step 4: For (c)(ii), the type of immune response is a cell-mediated immune response, and the cell involved is the cytotoxic T-cell (T-killer cell), which attacks the foreign graft cells.
\begin{center} OR \end{center} Sub-part (d):
Step 5: For (d), active immunity is developed by the body’s own immune system through exposure to a pathogen or vaccine, producing memory cells for long-term protection, while passive immunity involves the transfer of pre-formed antibodies (e.g., via mother’s milk or injections), providing immediate but temporary protection without memory cell formation.
Thus, B- and T-cells drive immune responses, humoral immunity involves antibodies in body fluids, graft rejection is due to MHC recognition by cytotoxic T-cells, and active immunity differs from passive by involving self-generated, long-term immunity.