Concept of Immunology:-

• The overall ability of the host fight against the disease causing organisms, provided by the immune system is called immunity.

• The immune system of our body consists of lymphoid organs, tissues, cell and soluble molecules like antibodies.
• The primary lymphoid organs are bone marrow and thymus. The secondary lymphoid organs like spleen, lymph nodes, tonsils, peyer's patches of small intestine and appendix.
• The bone marrow is the main lymphoid organ, where all blood cells including lymphocytes are produced. The thymus is a lobed organ, located near the heart and beneath the breast bone.
• Both bone marrow and thymus provide micro-environments for the development and maturation of T-lymphocytes. The spleen is a large been shaped organ. It mainly contains lymphocytes and phagocytes. It also reservoir of erythrocytes.
• The lymph nodes are located at different points along the lymphatic system. They trap the microbes or antigens. These antigens are responsible for the activation of lymphocytes causing the immune response.
• A lymphoid tissue is also located within the lining of the major tracts called Mucosal Associated Lymphoid tissue. It constitutes about 50% of the lymphoid tissue in human body.