BODY DEFENSE SYSTEM

animal/human must defend , against intruders;-pathogen… animal/human must defend , against intruders;-pathogen…??..bax, virus, fungi, pathogen from air, water, food, environment…. Body defense system/immunity? DEFINITION: ability of an organism to recognize and defend itself against pathogen resisting the attack of many dangerous organisms.

IMMUNOLOGY 201 Chapter 1: Body defense system Chapter 2 Innate Host Defenses

Outcome from today`s lesson… Understand innate and adaptive immunity Roles of innate immunity Component of innate immunity

Adaptive /acquired immunity Body defense system Innate immunity External Physical mechanical Internal Cellular Immune response Biological Molecular Adaptive /acquired immunity

DEFINITION: Innate and Adaptive immunity Host defenses that produce resistance against infection can be adaptive or innate Innate defenses: those that act against any type of invading agent Adaptive defenses: respond to particular agents called antigens (e.g. viruses and pathogenic bacteria) Only when our resistance fails do we become susceptible to infection by pathogens

Adaptive Defenses Respond to antigens by producing protein antibodies Also involve the activation of the lymphocytes Lymphocytes: specific cells of the body’s immune system Antibody and cellular responses are more effective against succeeding invasions by same pathogen than against initial invasions

Innate Defenses Physical barriers Chemical barriers Mechanical Barrier Cellular Barrier Inflammation Fever Molecular defenses

Comparison between innate immunity and adaptive immunity Non specific- acts against many organism Specific- respond to the specific antigen Present from birth Acquired- usually by having disease/ vaccination Heredity not Does not become more efficient after more exposure The immune system efficiency increased and memorized after exposure Various types of defense mechanism Involves mostly lymphocytes cell, that produces B cell and T cell

Physical Barriers Skin and mucous membranes protect your body and internal organs from injury and infectious agents These two physical barriers are made of cells that line body surfaces and secrete chemicals human beta-defensin-2 on human skin destroys pathogens by poking holes in bacterial membranes Mucosa covers those tissues and organs of body cavity exposed to exterior

Chemical Barriers High salt content of sweat inhibits bacteria from growing Sweat and sebum produced by sebaceous glands have low pH that inhibits growth of bacteria Acidic pH of stomach is a defense against intestinal pathogens Lysozyme: present in tears, saliva, and mucus, cleaves peptidoglycan linkage in bacterial cell wall

Mechanical barrier Function:- prevent/flush invading microbes in different type of mechanical way Hair and mucus- nasal, respirotary system Coughing and sneezing Urinary flow- remove microbes in urinary tract Tears and saliva – flush bacteria from eyes and mouth Vomitting and diarrhea- flush bacteria from digestive tract

Cellular Defenses – Defensive Cells Blood consists of about 60% liquid called plasma and 40% formed elements (cells) Formed elements: erthyrocytes, platelets, and leukocytes Leukocytes are defensive cells important to adaptive and innate host defenses

Formed cellular elements of the blood

Granulocytes Have granular cytoplasm and an irregularly shaped, lobed nucleus Include: Basophils: release histamine which helps initiate inflammatory response Mast cells: prevalent in connective tissue, release histamine, and associated with allergies Eosinophils: present in large numbers during allergic reactions Neutrophils (polymorphonuclear leukocytes): phagocytic cells that guard skin/mucous membranes against infection Dendritic cells: phagocytic cells that resemble nerve cells

Agranulocytes Lack granular cytoplasm with round nuclei Include: Monocytes: phagocytic cells derived from myeloid stem cells Lymphocytes: derived from lymphoid stem cells and contribute to adaptive host immunity Lymphocytes circulate in blood and are found in lymph nodes, spleen, thymus and tonsils

Phagocytes Cells that literally eat or engulf materials Monocytes, dendritic cell, neutrophils, eosinophils, Patrol, or circulate through body, destroying dead cells and cellular debris Guard the skin/mucous membranes against invasion by microorganisms Macrophages(formed from monocytes): “big eaters” that destroy not only microorganisms but also larger particles

Macrophage moving over a surface

The Process of Phagocytosis Phagocytes digest and destroy invading microbes and foreign particles by a process called phagocytosis Phagocytic cells must: Find Adhere to Ingest Digest the microorganisms

Phagocytosis of two bacterial cells by a neutrophil

Chemotaxis Phagocytes in tissues first must recognize invading microorganisms pattern recognition receptors (PRRs) on the phagocytic cells recognize molecular patterns unique to pathogen Phagocytes release cytokines that have specific roles in host defenses Chemokines: a class of cytokines that attract additional phagocytes to site of infection

Adherence and Ingestion The ability of the phagocyte cell membrane to bind to specific molecules on the surface of the microbe is called adherence Antiphagocytic capsule: the most common means by which bacteria avoid phagocytosis Complement system: coat microbes with antibodies to aid phagocyte in adherence Phagosome: pseudopodia fuse and enclose microorganism within this cytoplasmic vacuole

Digestion Phagocytic cells have several mechanisms for digesting and destroying ingested microbes Phagolysosome: lysosomes with digestive enzymes fuse with phagosome membrane Macrophages use other metabolic products to kill ingested microbes: Oxygen to form hydrogen peroxide Nitric oxide and superoxide ions

Extracellular killing What if the intruder is larger than the Macrophage/neutrophils? The killing need to be done extracellularlly by… Eosinophils- excreting toxic enzymes (MBP) –kill worm Natural killer cell- secrete cytotoxic proteins that kill intracellular

Molecular Defenses Involve the action of interferon and complement Interferon: interfered with viral replication in other cells Humans have three groups of interferon (alpha, beta, and gamma) Antiviral enzymes

Complement Refers to a set of more than 20 large regulatory proteins that play a key role in host defense General functions of the complement system are: Enhance phagocytosis Lyse pathogens directly Generate peptide fragments that regulate inflammation and immune responses Works as a cascade: a set of reactions that amplify some effect

Complement lesions in cell membranes

Activation of the classical complement pathway

The mechanism by which interferons alpha and beta act

Inflammation The body’s defensive response to tissue damage from microbial infection Characterized by signs: an increase in temperature redness swelling pain at infected or injured site

Steps in the process of inflammation and subsequent healing

Fever The elevation of body temperature to kill invading agents and/or inactivate their toxic products HOW? Raises temperature above opt. temp. of pathogens Microbial enzymes or toxins is inactivated Increase immune response Phagocytosis is enhanced Antiviral interferon production is increased Fever makes patient lie to rest.. Increased breakdown of lysosomes causing death of infected cell and microbes

A Summary of the body’s nonspecific defenses