Lymphocytes: it is a type of white blood cell that is part of the immune system. It is form of small leucocyte with a single round nucleus, occurring especially in the lymphatic system. lymphocytes are primarily involved in the body's immune response mechanism. This involves complex phenomena which end in the development of humoral and cellular immunity.
Humoral immunity: Humoral immunity involves the production of antibodies (immunoglobulins), and is brought about by lymphocytes, which are called B-cells. B-cells are bone-marrow derived lymphocytes.
cellular immunity: Cellular immunity includes delayed hypersentivity reactions, graft rejection, graft-versus-host reactions, defense against intracellular organisms, and probably defense against neoplasms. Cellular immunity is mediated by lymphocytes, which we called T-cells. T-cells are so named because they are dependent on the thymus for their production and development.