Identify A and B in the diagram below. Explain their role in the immune system of the body.

A – Lymph nodes B – Thymus -Role of Lymph nodes- acts as secondary lymphoid organ/provide site for interaction of lymphocytes with antigens which then proliferate to become cells/ serve to trap the microbes or other antigens which happen to get into lymph or tissue fluid /it activates the lymphocytes and cause immune response. -Role of Thymus- acts as Primary lymphoid organ / provide micro environment for the development and maturation of T- lymphocytes / provide site where immature lymphocytes differentiate into antigen sensitive lymphocytes .