Question

What do you understand by the immune system? Describe two main types of immune responses.

Answer 1

Hint:Immunity refers to the ability of the body to defend itself against disease-causing organisms. It is a complex biological system which has the ability to recognise and tolerate self and reject foriegn or nonself particles. When we talk about immunity we are majorly talking about the immune system of a person.

Complete answer:
The immune system is the defense system of the body. It provides a barrier against disease-causing organisms. The immune system comprises various types of cells and molecules. These cells and molecules protect our body against pathogens. Pathogens can be defined as everything from parasites to fungi, bacteria, viruses, and haptens. Haptens are molecules that may cause an immune response when they come in contact with a protein.
These cells and molecules are present in all the tissues of the body as well as lymphoid organs. Its prime role is to eliminate or prevent microbial infections. White blood cells or leukocytes are the most important cells involved in the immune system. They are mainly responsible for destroying disease-causing organisms or substances. Lymphoid organs, tissues, and proteinaceous molecules antibodies also play an important role in the defensive system.
The immune response is of two types:
1. Humoral Immunity: Humoral immunity is mediated by B cells. B cells secrete soluble substances called antibodies into the body fluids. Antibodies interact with the circulating pathogens like bacteria and other toxic molecules and kill them by the antigen-antibody reaction.
2. Cell-mediated Immunity: This is mediated by T cells which are called cytotoxic T cells. These cells are specific to a target cell that has been infected and kills the target cell by various mechanisms.

Note: It is to be noted that other main parts of the immune system include the spleen, thymus, antibodies, bone marrow, lymphatic system, and the complement system.