Immunology is a branch of biomedical science that deals with response of an organism towards an invading environmental factor. This process involves a complex interplay of invading particle and defence system of the host organism along with following cascading molecular mechanism to eliminate the invading agent. Cellular immunology is the study of the cells and molecules of an organism's immune system. It involves studying how these various cells and molecules work together to provide a defense against different types of pathogens.