(a) Innate & acquired immunity Innate immunity, also called inherent, natural, non specific immunity, comprises all those defence elements with which an individual is bom & which are always available to protect a living body. It acts on many organisms and does not show specificity, e.g. Lysozyme present in secretions such as tears, catalyzes the hydrolysis of molecules in the cell walls of bacteria & interferon induces antiviral state in non infected cells. They act as physiological barriers & check the growth of many pathogenic micro-organisms. Acquired immunity, also called adaptive or specific immunity, is the immunity obtained either from the development of antibodies in .response to exposure to an antigen, as from vaccination or an attack of an infectious diseases or from the transmission of antibodies as from mother to foetus through the placenta. (b) Active & passive immunity Active immunity is acquired by catching & surviving an infectious disease or by vaccination with a weakened form of the diseases which makes the body to form antibodies. Whereas passive immunity is conferred by transfer of immune products like antibodies etc. from other individual