Question

What do you understand by Immune System? Describe two main types of immune responses.

Answer 1

The immune system consists of all structures and processes that provide a defence against disease-causing pathogens.

The immune response is the specific reactivity which is induced by an antigenic stimulus in a host. The immune response is of two types:

1. Humoral Immunity: This is mediated by B cells by secreting soluble substances called antibodies into the body fluids. Antibodies interact with the circulating antigens like bacteria and other toxic molecules but they are not able to penetrate living cells.

2. Cell-mediated Immunity: This is mediated by T cells which are called cytotoxic T cells. These cells are specific to a target cell which has been infected and kills the target cell by various mechanisms.