27 At what two locations do most immune responses occur?in the blood; in the thymusat local sites of infection; in the bloodin draining lymph nodes; in the thoracic ductat local sites of infection; in draining lymph nodesO All of the above.

Immunity is the ability of the body to fight against the antigen or pathogenic substances by producing antibodies. In simpler terms, the immune response destroys, eliminates, or neutralizes foreign substances. It is generally of two types: innate immunity and acquired immunity. Innate immunity is present by birth and hence is also known as natural immunity while Acquired immunity is the ability of the body to fight against the foreign elements by providing specific resistance against it. This resistance is acquired during life and hence is known as acquired immunity or adaptive immunity.Lymphatic system is an organ system present in the vertebrates which is an important part of the cardiovascular system and the immune system. The bone marrow and thymus are the primary organs and tonsil, adenoids, spleen, are secondary organs of the lymphatic system which are responsible for gathering the antigens before the mature lymphocytic cells and initiate adaptive immune response at the site of infection. The lymphatic system is comprised of lymph vessels and lymphoid organs and numerous lymph nodes. The lymph is a interstitial fluid found inside the lymph nodes and vessels which contain immunoglobulins. The components of the lymphatic system gather liquid from the body and return it to the cardiovascular circulation through thoracic duct. White blood cells or leukocytes play important role in both specific and non-specific immunity. Myeloid progenitor cells give rise to red blood cells and white blood cells, B-cells and T-cells and natural killer cells which are important components of immune response. Hence, at all the locations i.e., blood, thymus, lymph nodes, thoracic duct, site of infection, immune response occurs. Correct option is: All of the above.