Reactivity of C=C C—C Electrons in pi bond are loosely held Electrophiles are attracted to the pi electrons. · Carbocation intermediate forms. Nucleophile adds to the carbocation. · Net result is addition to the double bond
① Lymphocyte: a. T-lymphocytes: cytotoxic T cell: Tc C- kill the tumor cell, virus infective cell and foreign cell helper T cell: Th C- promotes activity of BLC and Tc C suppressor T cell: Ts C –regulate the function of BLC and TC