Download Immunology courses lecture notes and more Lecture notes Biology in PDF only on Docsity!
Basics of Immunology (31351 )
Immunity is concerned with the recognition and disposal of foreign or ‘non-self’ material that enters the body, usually in the form of life-threatening infectious microorganisms. The immune system comprises a range of cells, tissues and chemicals that interact to overcome infection, repair tissue damage and maintain the integrity of the body. The immune response is affected by the food we eat, environmental, genetic, neurological and psychological influences. The defense of a host towards foreign bodies can be divided into Innate Immunity and Acquired Immunity. Innate immunity is present continuously, it is a defense mechanism that is present from birth. Acquired immunity is induced by the presence of foreign material and is usually quite specific. What happens when The immune system goes wrong? persistent or fatal infections, allergy , autoimmune disease, transplant rejection. The Functions of Immune system? -Protecting the organism of pathogens invasion.
**_- considered as haemostatic mechanism eliminating the dead and damaged cells off the living tissues.
- destruction of mutant and infected cells (cancerous cells, viral infected cells)._**
1. Innate Immunity: 1.1 Physical Barriers: - skin acts as a physical barrier - mucous membranes in the respiratory, gastrointestinal, urogenital tract trap bacteria which are subsequently removed by ciliated cells.
Cells and molecules of the innate immune system Natural Killer (NK) cells ( Lymphocyte)
- Identify and kill virus-infected and tumour cells.
- use complex recognition system ( recognise HLA molecule of virus infected cell or tumour, and kill them.) Monocytes , Macrophages and Dendritic cells ( Phagocytes and Antigen presenting cells)
- Mononuclear phagocytes.
- Two main functions: 1. “garbage disposal” - 2. Present foreign cells to immune system. Granulocytes (PMNs) Neutrophils, Eosinophils, Basophils and mast cells.
- Several molecules that recognize and respond to microbes and promote innate Responses exist in soluble forms in blood and ECF.
- provide early defense against pathogens present outside host cells at some stage of their life cycle.
- Function in two way :- Binds to microbes and act as opsonins to enhance phagocytosis by macrophage Neutophils and Dendritic cells. Promote inflammatory responses that bring more phagocytes to sites of infection and may also directly kill microbes.
- Complements system proteins , Antimicrobal peptides , Cytokines, Acute phase proteins.
Acquired/Adaptive Immunity Characteristics Antigen specific. Can form Immunological memory. Requires priming- specific cells help to start the acquired immune response. Slow to develop. Two types Cellular Immunity: (Tcells ) Humoral immunity: ( B cells & antibodies ) Antigens are glycoprotein molecules which react with antibodies or T cells. Not all antigens can induce an immune response in the host: those that can are termed Immunogens. Antibody molecules can be found in the blood stream and the body fluids and bind specifically to particular molecules termed antigens. They are the acquired component of the humoral immune response.
Basics of Immunology (31351 )
Organization of the Components of the immune system ( Cells and tissues of the immune system)
- The primary function of innate immunity is the recruitment of immune cells to sites of infection and inflammation through the production of cytokines (small proteins involved in cell-cell communication). -The innate immune response also promotes clearance of dead cells or antibody complexes and removes foreign substances present in organs, tissues, blood and lymph. It can also activate the adaptive immune response through a process known as antigen presentation.
- Adaptive immunity develops when innate immunity is ineffective in eliminating infectious agents and the infection is established.
- The primary functions of the adaptive immune response are the recognition of specific “non- self” antigens in the presence of “self” antigens; the generation of pathogen-specific immunologic effector pathways that eliminate specific pathogens or pathogen infected cells; and the development of an immunological memory that can quickly eliminate a specific pathogen should subsequent infections occur. Primary lymphoid organs (thymus & bone marrow) for production of lymphocytes (lymphopoeisis). Secondary lymphoid organs help antigen to come into contact with lymphocytes expressing appropriate specific receptors(including spleen, lymph nodes, mucosal associated lymphoid tissues MALT.)
- Lymphocyte numbers are carefully regulated, and they recirculate.
- T cells recognise processed antigen presented by MHC molecules.
- B cells recognise intact, free antigen.
- Important APCs are dendritic cells, B cells, and macrophages.
This process of arriving at the mature cell phenotype is known as differentiation. The immature precursor cells themselves develop from progenitor cells that are thought to have a common origin – the pluripotent or common haemopoietic stem cell – found in the bone marrow. These cells are able to renew themselves by proliferation and are able to differentiate into progenitor cells.
2- Thymus The thymus is the site of T cell maturation. The lymphocytes in the thymus, also called thymocytes, are T lymphocytes at various stages of maturation. Maturation begins in the cortex and as thymocytes mature they migrate toward the medulla, so that the medulla contains mostly mature T cells. Only mature T cells exit the thymus and enter the blood and peripheral lymphoid tissue.
- lymph, ( lymph **= clear fluid) flows in lymphatic vessels, lymphatic tissue and red bone marrow.
- The content of lymph is the same as interstitial fluid, the fluid around tissue cells. Lymph eventually drains into venous blood.** Lymph drains interstitial fluid, transports dietary lipids and facilitates immune responses.
- lymphatic capillaries absorb the fluid from the space between tissue cells.
- The absorbed fluid is called lymph is pumped into larger lymphatic vessels. These vessels merge into afferent lymphatics that drain into lymph nodes, and the lymph out of the nodes goes through efferent lymphatics.
- The lymphatic system collects microbial antigens from their portals of entry and delivers them to lymph nodes, where they can stimulate adaptive immune responses.
- The microbial antigens are capture by dendritic cells and enter the lymphatic vessel.
- The lymphatic system acts as a filter, that sample the antigens in the lymph before they reach the blood vessels and permit the antigens to be seen by the adaptive immune system.
1- Lymph nodes
- encapsulated, vascularized secondary lymphoid organs. The lymph is filtered by lymph nodes.
- B and T lymphocytes are sequestered in distinct regions of lymph nodes, each region with its own unique architecture of reticular fibers and stromal cells.
- The anatomic segregation of B and T lymphocytes in distinct areas of the node is dependent on cytokines that are secreted by lymph node stromal cells in each area
2- Spleen The blood is filtered by the spleen.( the body's largest lymphatic organ. It is important for antibody production, facilitating immune responses to blood borne antigens ) spleen is made up of two distinct tissue types:
- Red pulp is the site of blood filtration in the spleen. made of connective tissue called the cord of Billroth that can fill with blood and contains many macrophages.
- White pulp is secondary lymphoid tissue that is similar to that in the adenoid tonsils. They contain large amounts of lymphocytes and antigen -presenting cells. The primary function of the spleen is blood filtration. Blood cells have a lifespan of roughly 120 days. When blood passes through the red pulp of the spleen, healthy blood cells easily pass, while older red blood cells are caught phagocytized by the macrophages within. The macrophages also remove pathogens, denatured hemoglobin, and other cellular debris. Antigens are also filtered by the red pulp, which may be presented to naive lymphocytes in the white pulp of the spleen. This stimulates the same type of adaptive immune response that occurs in the lymph nodes. Individuals who do not have a spleen are highly susceptible to infections with encapsulated bacteria.
3- Mucosa Associated Lymphoid Tissue (MALT)
NALT (The nasal-associated lymphoid tissue)
- composed of the lymphoid tissue at the back of the nose (pharyngeal, tonsil, and other tissue) and that associated with Waldeyer’s ring (palatine and lingual tonsils). Its location suggests that they are directly involved in handling airborne microbes. BALT ( Bronchus-associated lymphoid tissue) similar to Peyer’s patches in GALT. composed mainly of aggregates of lymphocytes organized into follicles that are found in all lobes of the lung and are situated under the epithelium, mainly along the bronchi. Antigen sampling is carried out by epithelial cells lining the surface of the mucosa and by way of M cells which transport antigens to underlying APCs and lymphocytes.
GALT Gut-associated lymphoid tissue
is composed of lymphoid complexes (also called Peyer’s patches in the ileum) that consist of specialized epithelium, antigen-presenting cells, and intraepithelial lymphocytes. These structures occur strategically at specific areas in the digestive tract.
