Elaborate Immune Response system and their categories?

The immune response is a group of defenses that the body has developed to combat disease-producing agents, or pathogens. The most common pathogens are bacteria, viruses, fungi, protozoa, and a few invertebrate multicellular organisms.

One of the primary means of defense against invasion by pathogens is the normal body flora; that is, bacteria and fungi that live and reproduce in great numbers on skin surfaces, mucous membranes, and in the gastrointestinal tract. The natural flora compete with pathogens for nutrients, and some produce inhibitory compounds that are toxic to pathogens. Other lines of defense include mucus and cilia in the respiratory tract, an enzyme called lysozyme in tears and saliva, acid in the stomach, bile salts, and the acid secreted by the vagina.

The immune response can be divided into two categories: non-specific and specific defenses. One of the non-specific defenses are the phagocytes. The phagocytes involved here are of two types: neutrophils, small white cells with irregular nuclei; and macrophages, large white cells. Pathogenic microorganisms become attached to the membrane of a phagocyte, and engulfed in an endocytic vesicle by phagocytosis. Lysosomes then fuse with the vesicles, and destroy them with enzymes called lysozymes. A single phagocyte can lyse (break down) up to 25 bacteria.

Another non-specific defense against pathogens is inflammation, a generalized body response to infection, mechanical injuries, and burns. The blood capillaries in the affected tissues become more permeable ("leaky"), and plasma and some white blood cells escape into the surrounding tissues where they can deal with the problem. In these cases, problems might range from fighting off invading viruses or bacteria to cleaning up broken cell parts or dead cells.

Infection that extends throughout the body, or generalized infection, is accompanied by fever. Elevated temperature actually slows growth or kills certain pathogens. However, if the temperature is too high, it can damage body tissues, particularly brain cells. Viral infections cause the infected cells to produce small amounts of a glycoprotein substance called interferon. Interferon interferes with the replication of viruses. Interferons affect any type of virus. Genetic engineers are able to synthesize interferon in vitro; that is, in the laboratory, and it is being used to combat many types of viral diseases.