12.2A: Immunoassays for Disease
- Describe how immunoassays aid in the diagnosis of disease
The Immune System
Immunology is the study of molecules, cells, and organs that make up the immune system. The function of the immune system is to recognize self antigens from non-self antigens and defend the body against non-self (foreign) agents. Through specific and non-specific defense mechanisms, the body’s immune system is able to react to microbial pathogens and protect against disease. The first line of defense against infection is intact skin, mucosal membrane surfaces, and secretions that prevent pathogens from penetrating into the body.
When a foreign agent penetrates the first line of resistance, an immune reaction is elicited and immune cells are recruited into the site of infection to clear microorganisms and damaged cells by phagocytosis. If the inflammation remains aggravated, antibody-mediated immune reaction is activated and different types of immune cells are engaged to resolve the disease. The immune system is composed of cellular and humoral elements. The cellular component includes mast cells, neutrophils, macrophages, T and B lymphocytes, and plasma cells. The humoral component includes complement, lyzozyme, interferon, antibodies, and cytokines. All work cooperatively to eliminate immunogenic foreign substances from the body.
Immunoassays
To aid in the diagnosis of disease caused by infectious microorganisms, immunoassays have been developed. These biochemical and serological techniques are based on the detection and quantitation of antibodies generated against an infectious agent, a microbe, or non-microbial antigen.
Because antibodies can be produced against any type of macromolecule, antibody-based techniques are useful in identifying molecules in solution or in cells. A blood sample is collected from the patient during the acute phase of the disease when antibody levels are high. Serum is then isolated and the concentration of antibodies is measured through various methods. Most assays rely on the formation of large immune complexes when an antibody binds to a specific antigen which can be detected in solution or in gels. Recent methods employ pure antibodies or antigens that have been immobilized on a platform and that can be measured using an indicator molecule. These methods provide high sensitivity and specificity and have become standard techniques in diagnostic immunology.
Key Points
- When microbial agents penetrate the body, they elicit an immune response that involves cellular and humoral components.
- An immune response is usually characterized by antibody secretions. These can be measured in the laboratory through various biochemical and serological techniques.
- Most immunoassays rely on the formation of antibody- antigen complexes that can be identified using an indicator molecule.
Key Terms
- humoral : Of or relating to the body fluids or humours.
- antibody : A protein produced by B-lymphocytes that binds to a specific antigen.