Introduction to Immunochemical Techniques

Life on the earth has an abundance of pathogenic and non-pathogenic microbes, which apart from mutual symbiotic and survival connections contain several toxic and allergenic molecules that bring about imbalance in homeostasis. These substances have a variety of mechanisms to disturb the functioning of their host. To counter these threats, mammals developed a complex and evolutionary matured array of immune and defensive mechanisms to check or annihilate these substances without damaging their own tissues. In general, there are two mechanisms which permit recognition and destruction of microbial, toxic, or allergenic substances: 1) Innate response: This is the first line of defense against the invading pathogen or toxin, and 2) Adaptive response: The second line of defense. Although the adaptive responses are temporary, they leave a memory associated with this process and for a specific antigen. The organism resorts to the same defense mechanism when it encounters the same antigen again. The adaptive response has the capability to regulate immune memory, and create an effective and specific host response against invading pathogens, even decades after the first encounter.

For identification of foreign material, immunoglobulins (IgG) and antibodies are integral parts of adaptive immune response in mammals. IgGs are present in the tissues and fluids of all vertebrates. Research related to antibodies started way back in 1890, when Emil von Behring and Shibasabura Kitasato began to immunize infected animals against diptheria. According to the side-chain theory, proposed by Paul Ehrlich in 1900, the pathogens bind to their side-chain receptors. Then, the modern era of antibody research and discovery started with examination at the atomic level of details of its structure (in 1973) and invention of monoclonal antibodies (in 1975).

The formation of an antigen–antibody complex, is due to a very specific interaction between antibody and its antigen, and is the basis of all immunochemical based technology. An antigen in general, is an exogenous substance that elicits an immune response and is recognized by very specific antibodies produced by the immunological responses to counter the invading antigen. They are usually either proteins or polysaccharides of high molecular weight. However, small molecules can also function as antigens, such as polypeptides, lipids, and nucleic acids. These small molecules (haptens) may generate immune response by coupling themselves to a larger “carrier protein”, such as bovine serum albumin or hemocyanin or other synthetic matrices.