Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. The immune system is the body's defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune system attacks organisms and substances that invade our systems and cause disease. The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. The immune system is the body’s natural defence in combating organisms. The immune system usually have two lines of defence: the innate immune system representing a non-specific (no memory) response to antigen (substance to which the body regards as foreign or potentially harmful) and the adaptive immune system, which displays a high degree of memory and specificity. The innate system represents the first line of defence to an intruding pathogen and includes various cells like the natural killer (NK) cells, mast cells dendritic cells and phagocytes. Besides there are molecules like complement, acute phase proteins (APP) and interferons (IFNs) which work in concert with the cells of the innate immune system and which foster close functional links with their adaptive counterpart. The adaptive immune system is further divided into humoral and cellular components.  Cell-mediated immunity, also known as delayed-type hypersensitivity (DTH) or Type IV Hypersensitivity, is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells (NK), antigen-specific cytotoxic T-lymphocytes, and the release of various