Chapter 1. MAIN CONCEPTS
Immunology is a science about immunity. In the Russian Federation "Allergology and Immunology" is an official medical specialty that teaches structure and functions of the human immune system in normal and pathological states, including immune system disorders. In the wide sense of the word, immunology studies an organism's defense against genetically foreign factors by means of the immune system.
Organism protective systems
A multicellular organism needs to defend its internal medium against penetration and destructive action of various external substances and objects (Fig. 1-1). This task is performed by two components: nonspecific (innate protective mechanisms) and specific (adaptive immunity). The following biological mechanisms are involved:
► Integumentary tissues (skin, mucous membranes).
► Microbicidal secretions (hydrochloric acid of stomach, bactericidal compounds of saliva, digestive enzymes in the gastrointestinal tract, etc.).
► Vascular reactions prevent external factors from penetrating inside the body (quick swelling at the site of injury).
► Acute-phase proteins - C-reactive protein (CRP) and mannose-binding lectin (MBL). They are synthesized by liver cells (hepatocytes). These proteins are able to bind the blood-infecting bacteria, viruses and unicellular fungi. Phagocytes express specific receptors (Rc) that bind complexes of acute-phase proteins and microorganisms. Therefore, acute-phase proteins may function as opsonins.
► Phagocytosis of microbes by neutrophils and macrophages. This evolutionary conserved innate cellular defense mechanism originates from the alimentary function of unicellular organisms. The same cell - phagocyte - will attempt to take up various objects in order to digest.