Biochain

The lymphoid system or lymphoid tissue is made up of all the organs where lymphocytes and other immune system cells reside. There are two types of lymphoid organs: the primary or central lymphoid organs (such as the bone marrow or the thymus) and the secondary or peripheral lymphoid organs (such as the lymph nodes or the spleen). Lymphocytes, the effector cells of the adaptive immune response and the main components of the lymphoid organs, are produced, developed and selected in the primary lymphoid organs and are activated to perform their effector functions in the secondary lymphoid organs, which are thus the site of initiation of the adaptive response. In the primary lymphoid organs, T and B cells differentiate from lymphoid progenitors, proliferate and are selected. The secondary lymphoid organs are the site of activation of naive lymphocytes, and thus the starting point of the adaptive immune response.