9. Immune System Complete Study Guide_ Guaranteed Success.

5. The lymph nodes - The lymph nodes present along network of the lymphatic vessels that located in all the body parts under the armpits, at the two sides of the neck ,in upper thigh, and near the internal body’s organs. Their size ranging from a pinhead, to the seed of small beans. The node is divided internally into pockets filled with B- lymphocytes, T- lymphocytes, and macrophages and some other types of white blood cells that get rid of germs and the debris cells. • They purify the lymph from any harmful substances or microbes and store white blood cells (lymphocytes) that help in fighting against any disease or infection. • Each lymph node is connected with several lymph vessels that transfer the lymph from the tissue to the nodes for the filtration of the lymph to get rid the suspended foreign pathogen away from the body. The Lymphocytes They form about 20%: 30% of the white blood cells in blood, All Lymphocytes are formed in the red bone marrow, At the beginning they do not have any immune ability, but they pass in the process of maturation and differentiated in the lymphoid organs after that it changes into cells that have the ability of immunization. 3 | P a g e - They revolve in the blood to search for any microbe or foreign body, their defense and immune mechanisms to get rid of the pathogenic microbes to invade the body, reproduce, and spread through it and sabotage its tissue and disruption of its vital physiological functions. There are three types of lymphocytes in the blood which are: 1. B- cells: represents 10-15% of the lymphatic cells, are formed in the bone marrow and complete their growth to become mature. - Their function is the identifying any microbes or foreign materials (such as bacteria or virus), then adhere this foreign material and produces antibodies for his material to destroyed it. 2. T- cells: form about 80% of lymphocytes, and mature in the thymus gland where they differentiate into several types: • Helper T cells (TH): activate other types of T cells and stimulate it to do their responses, as well as stimulate B cells to produce antibodies • Cytotoxic T-cells: (or killer T cell) (Tc): attacking to the foreign cells where. It kills carcinogenic cells, the transplanted organs and body cells infected with the virus. • Suppressor T-cells (Ts): They regulate the degree of immune response required to limit and discourage or inhibit the action of T cells and B cells after elimination the pathogen. 3. Natural killer cells (NK): form about 5% to 10% of lymphocytes in blood, and they are produced and mature in the bone marrow. The other white blood cells - They are the basal cell (Basophils), acidic cells (Eosinophils) and neutral cells (Neutrophils). • They are distinguishable from their size and the shape of the nucleus and the color of granules phenomenon appeared inside by using the microscope. • These granules have the main role in the disintegration of the pathogen’s cells attacking the body, ingest and digest the pathogens (phagocytosis) so they struggle the infection specially, the bacterial infection and inflammations. This, in addition to a single-core Monocytes cells that destroy foreign bodies, and change into phagocyte cells when needed, and engulf the foreign organisms. 4 | P a g e Macrophages Including two types: 1. The fixed macrophages: They are large phagocyte cells; their types and names depend on the tissues where they exist. They are found in most body tissues and ready to engulf foreign particles as well as microorganisms. 2. Mobile macrophages: They offer information which are collected about microbes and foreign particles to the specialized immune cells found in lymph nodes scattered in different body parts. Immune cells prepare suitable defense mechanisms such as antibodies and specific types of killer cells that deal with these microbes. Assisting chemical substances - Pathogen recognition triggers the production and release of a variety of peptides and proteins that attack pathogens or impede their reproduction. These chemicals help and cooperate the specialized mechanisms of the immune system; they are many chemicals such as: 1. Chemokines: They recruit (guide migration) of large circulating phagocyte cells which are found in blood with large number to sites of existence of microbes or foreign particles to prevent their reproduction and spreading. 2. Interleukins: They mediate communication between different immune cells on one hand and between immune system and different body cells on the other hand, they help the immune system to perform its defense function. 3. Complement system: consists of 30 different types of proteins. These proteins circulate in an inactive state and are activated by substances on the surface of many microbes. Activation results in a cascade of biochemical reactions that can lead to lysis (bursting) of invading cells, which makes them easily engulfed by phagocytes. The complement system also functions in the inflammatory response. 4. Interferons: These are different types of proteins that provide innate defense by interfering with viral infections. They are produced by cells of tissues infected by viruses. Interferons are not specific for certain virus, they bind to healthy cells neighboring to the infected cells and induce them to produce enzymes that inhibit the action of replication enzymes of the virus, thus preventing the virus nucleic acids from reproduction and spreading in the body. 5 | P a g e • Some white blood cells secrete a different type of interferon that helps activate macrophages, enhancing their phagocytic ability. There are two systems of immunity in man: 1. Natural (non-specific or innate) immunity 2. Acquired (specific or adaptive) immunity. - Although the two systems of immunity are different, they work together in a cooperation and harmony, in which each of them uses different mechanisms that activate the immune response of the other system, i.e., they activate each other to help the body to deal successfully with pathogens. Natural (non-specific or innate) immunity This immunity is a group of defense mechanisms that protect the body and is characterized by rapid, effective response to resist, fight and destroy any microbe or foreign body that invades the body, these mechanisms are nonspecific against specific type of microbes or antigens and can be classified into two lines of defense, as follows: Barrier defense It includes a group of physical natural barriers in the body such as the skin, mucus, tears, sweat, and hydrochloric acid of the stomach. The main function of this line is preventing pathogens from entering the body. • The skin: which is characterized by a tough horny layer on its surface, which acts as a barrier that difficult to be penetrated or to pass through. Also, the sweat, secreted by the sweat glands on the skin surface, can kill most of the microbes because of its salinity. • The Cerumen (ear’s wax): a substance secreted by the ears that can kill microbes, thus protecting the ears. 6 | P a g e • The Tears: which protect the eye from microbes because it contains enzymes which lysis the microbes. • The Mucus in the respiratory tracts: which is a viscous fluid that lines the respiratory bronchi to adhere with the microbes, and foreign bodies, entering with air, then the mucus together with the trapped microbes is expelled to the outside of the body by the action of the beating cilia lining these tracts. • The Saliva: which contains substances that kill microbes, in addition to enzymes that can dissolve such microbes. • The acidic gastric juice: the epithelial lining of the stomach produces and secretes the strong hydrochloric acid that can kill microbes entering with food. Cellular Innate Defenses - Pathogens entering the mammalian body are subject to phagocytosis. Phagocytic cells detect fungal or bacterial components using several types of receptors, some of which are very similar to the Toll receptor of insects. - Each mammalian Toll-like receptor (TLR) binds to fragments of molecules characteristic of a set of pathogens. • TLR3, on the inner surface of vesicles formed by endocytosis, is the sensor for double-stranded RNA, a form of nucleic acid characteristic of certain viruses. • TLR4, located on immune cell plasma membranes, recognizes lipopolysaccharide, a type of molecule found on the surface of many bacteria. • TLR5 recognizes flagellin, the main protein of bacterial flagella. - In each case, the recognized macromolecule is normally absent from the vertebrate body and is an essential component of certain groups of pathogens. - After detecting invading pathogens, a phagocytic cell engulfs them, trapping them in a vacuole. The vacuole then fuses with a lysosome, leading to destruction of the invaders in two ways. 7 | P a g e • First, gases produced in the lysosome poison the engulfed pathogens. • Second, lysozyme and other enzymes in the lysosome degrade the components of the pathogens. - The two main types of phagocytic cells in the mammalian body are neutrophils and macrophages. • Neutrophils, which circulate in the blood, are attracted by signals from infected tissues and then engulf and destroy the infecting pathogens. • Macrophages (“big eaters”) are larger phagocytic cells. Some migrate throughout the body, whereas others reside permanently in organs and tissues where they are likely to encounter pathogens. o For example, some macrophages are located in the spleen, where pathogens in the blood become trapped. - Two other types of phagocytic cells—dendritic cells and eosinophils—provide additional functions in innate defense. • Dendritic cells mainly populate tissues, such as skin, that contact the environment. They stimulate adaptive immunity against pathogens they encounter and engulf. • Eosinophils, often found beneath mucosal surfaces, have low phagocytic activity but are important in defending against multicellular invaders, such as parasitic worms. Upon encountering such parasites, eosinophils discharge destructive enzymes. - Cellular innate defenses in vertebrates also involve natural killer cells. These cells circulate through the body and detect the abnormal array of surface proteins characteristic of some virus-infected and cancerous cells. • Natural killer cells do not engulf stricken cells. Instead, they release chemicals that lead to cell death, inhibiting further spread of the virus or cancer. - Many cellular innate defenses of vertebrates involve the lymphatic system, a network that distributes the fluid called lymph throughout the body. • Some macrophages reside in the structures called lymph nodes, where they engulf pathogens that have flowed from the interstitial fluid into the lymph. 8 | P a g e • Dendritic cells reside outside the lymphatic system but migrate to lymph nodes after interaction with pathogens. Within the lymph nodes, dendritic cells interact with other immune cells, stimulating adaptive immunity. Inflammatory response - It is a nonspecific defense mechanism in the area of injury as a response to the damage of tissues caused by the injury or by the infection. Inflammation leads to some changes that takes place in the area of injury: o The blood vessels dilate to the maximum limit because of secreting large quantities of inflammation-generating substances, the most important one is the histamines, that are secreted by specific cells like mast cells and basophils. o Thes