Immunology Lec. 2 A -2024-2025_Converted.pdf

Immunology Types of immunity Immunity(resistance): is the sum of all naturally occurring defense mechanisms that protect the humans from the infectious diseases. Two types of immunity: First. Non-specific (innate) immune response Second. Specific (acquired)  Innate...

Immunology Types of immunity Immunity(resistance): is the sum of all naturally occurring defense mechanisms that protect the humans from the infectious diseases. Two types of immunity: First. Non-specific (innate) immune response Second. Specific (acquired)  Innate Immunity Innate immunity (also called natural immunity or native immunity). Innate immunity: provides the body’s first line of defense against microbial and non microbial agents. this type of immunity does not required memory so the component of this system can reacted on first exposure to the invading organism or non microbial substance (Antigen) Ag. Antigen: substance that is capable of stimulating an immune response, specifically activating lymphocytes, which are the body’s infection-fighting white blood cells. Two main divisions of antigens are recognized: 1- Foreign antigens (heteroantigens) 2- Autoantigens (self-antigens). Innate Immunity It is the first line of defense against invading organisms. Exist before or react immediately after contact with pathogen. Structures, chemicals, processes that work to prevent pathogens entering the body. Innate immunity is the initial response to infection  Characteristics of Innate Immunity : 1. Non specific: Directed and effective against wide range of Antigen (Ag). 2. Natural: Present at birth and doesn’t require previous exposure. 3. No memory Immunity: Doesn’t improve with repeated exposure to the same Ag.  Determining Factors of Innate Immunity: 1- Genetic factor: a- Species level b- Race level. c- Individual level. 2. Age(e.g elderly). 3. Hormonal status(e.g corticosteroids) 4. Nutritional status(e.g malnutrition).  Mechanism of Innate Immunity: 1- Barriers factors: Prevent entry of microorganism into the body. A. Physical barriers: 1) Skin; − Most important one. − Presence of lactic acid in fatty secretion. 2) Mucus membrane: − Covering the internal surfaces of body. − Prevent attachment of organism to epithelial cell.  Innate Immunity B. Mechanical barriers: 1- Ciliary movement, sneezing, coughing. 2- Washing action of body fluid: tears, saliva & urine. : C. Physiological barriers 1- Bactericidal substances: HCL in stomach, lysozyme in tears. 2- Normal bacterial flora (commensal): Lactobacilli in vagina produce chemical substance suppresses the growth of pathogenic organism. 3- Sweat glands Salt- inhibits growth of pathogen by drawing water fr their cells. 4- Antimicrobial peptides. 5- Lysozyme- destroys cell wall of bacteria( peptidoglycans). 2- Cellular Factors: Phagocytic cell, NK cells, Dendritic cells and Other cells participating in innate immunity Recognition of the Pathogen Associated Molecular Patterns (PAMPs) by cell receptors. (PAMPs) − Structures common for certain groups of pathogens and essential for their life, replication and/or infectivity. − Not present on human cells, Examples: Structures of bacterial cell wall (LPS, peptidoglycan...) Nucleic acids of pathogens (ds RNA). 3- Humeral Factors: Complement system. Cytokines. Acute phase protein = C-Reactive Protein (CRP), fibrinogen. Humoral factors: ( contribute to non specific I.R) A. Antibody and complement : normal serum can kill and lyse some gram-ve bacteria this property probably is the result of combined action of Abs. And complement, both of which present in normal serum B. Non-Abs. humoral factors: 1. chemotactic factors: which attract phagocyte at the site of infection, like C5a C3a. these are generated during complement activation. 2. Interferon (INF): are proteins that usually are produced when there is viral Infection( anti viral action ) ex.  INF-alpha secreted by macrophages  INF-beta secreted by fibroblast  INF-gamma secreted by T-cells after stimulation. 3. lactoferrin and transferrin: are protein found in milk and serum respectively which compete with bacteria for iron. 4. lysozyme: hydrolyze the mucopeptide layer of the cells of many bacteria Phagocytosis: Phagocytosis is an important feature of cellular innate immunity performed by phagocytic cells Phagocytic cells have ability to engulf or eat and then ingest or kill the pathogens or particles. Phagocytes generally patrol the body searching for pathogens, but can be called to specific locations by cytokines. The pathogen is killed by the activity of digestive enzymes or following a respiratory burst that releases free radicals into the phagolysosome. It is an active process requiring enzyme and involving following steps:Continue Phagocytosis: It is an active process requiring enzyme and involving following steps: 1. Chemotaxis: The directed movement of a cell along the attracting molecule. − most potent chemo attractant are C5a, IL – 8, from damage cells. 2. Attachment to organism. 3. Formation of pseudopodia. 4. Fusion of pseduopodia & phagosome formation 5. Fusion of phagosome with lysosomes to form phagolysosome. Phagocytic cells: Phagocytes are two types: 1. Mononuclear phagocytes. − Monocytes = in the blood. − Macrophages = in the tissues for example kupffer cells are macrophage in the liver. and Histiocytes are macrophage in connective tissue. 2. Polymorphonuclear granulocytes (PMNs). − Neutrophils can also release granules and cytotoxic substances extracellularly. Killing pathway of phagocytes: 1- Oxygen dependent microbicidal system. Oxygen is metabolized into toxic metabolites. It is more toxic mechanism. 2- Oxygen independent microbicidal system. By lowering pH. Enzymes proteolytic and hydrolytic enzymes. Others: lactoferrin.. : Lymphocytic cells: ( contribute non specific I.R) Certain lymphocytic cells are cytotoxic against a variety of targets in the absence of any previous exposure to the target. Ex. Of these cells A. Natural killer cells (NKCS):  granular lymphocyte that appear to function in immune surveillance  naturally occurring cytotoxic lymphocytes that exist in the body, activated by IL-2.  arise from bone marrow precursors but a lineage distinct from that of either T-cells or B-cells.  contribute 10-15% of lymphocytes in peripheral blood.  cytotoxic for tumor cells and virally infected cells, also play a role in resistance to some bacterial, fungal and parasitic infection.  Mode of killing is extra cellular killing. B. Ab-dependant cytotoxic cells: can kill target cells without the participation of complement if the target cells are coated with specific antibody. The cells that participate in antibody dependant cellular cytotoxicity (ADCC) have a membrane receptor for FC portion of IgG molecule this serve as an anchor between the cytotoxic cells and its target Type of cells: NKCs, macrophages and neutrophils C. lymphokine - activated killer cells (LAK cells). Protective barriers of the body. The barriers of the body represent the first line of defense and prevent or retard the.entry cells and molecules into the body