6a video 1

2nd and 3rd lines of defense are what most people consider the “immune system”

\ What are Antigens? NONSELF: includes an enormous variety of materials Also called an immunogen Proteins and polysaccharides good antigens Lipids and nucleic acids often are not Think 2nd and 3rd line of defense Immune system recognizes and responds to only a portion of the antigen - the epitope Types of antigens Mosaic antigens - very complex with numerous component parts, each of which elicit a separate lymphocyte response Haptens: small foreign molecules that consist of only a determinate group Superantigens: bacterial toxins, potent stimuli for T cells Allergens: antigens that evoke allergic reactions First line of defense Normal microbiota Not technically part of immune system However, provides significant protection Protects through competitive exclusion Covers binding sites Pathogens cant bind Competes for nutrients Nutrients unavailable for pathogens Skin Provides the most difficult barrier to penetrate Composed of two main layers Dermis Contains tightly woven fibrous connective tissues Makes extremely tough Epidermis Composed of many layers of epithelial cells As cells reach surface, they become increasingly flat Outermost sheets of cells embedded with keratin Makes skin water-repellant Outer layers slough off, taking microbes with it Other cutaneous barriers Hair shaft and follicle cells periodically “shed” Sweat glands help to flush microbes Mucus membranes Digestive, urinary, and respiratory tracts and the eye are all moist and permeable Mucus membranes Constantly bathed with mucus (help with surfaces) Some mucous membranes have mechanisms to propel microorganisms and viruses to areas where they can be eliminated (cilia in respiratory tract) Mucous coat on some membranes impedes entry and attachment Blinking and tear production flush the eyes Constant flow of saliva move microbes into stomach Vomiting and defecation evacuate noxious substances from the body Nonspecific chemical defenses Lactic acid and electrolyte concentrations of sweat Skins acidic pH and fatty acid content HCI in the stomach Digestive juices and bile in the intestine Acidic pH in the vagina Semen- antimicrobial chemical → Sebaceous secretions and specialized glands- antimicrobial chemicals → Antimicrobial substances Lysozyme Enzymes that degrade peptidoglycan Found in tears, saliva, blood, and phagocytes Peroxidase Found in saliva, body tissue, and phagocytes Breaks down hydrogen peroxide to produce reactive oxygen Lactoferrin Sequesters iron from microorganisms Iron essential for microbial growth Found in saliva, some phagocytes, blood and tissue fluids Defensins Antimicrobial peptides inserted into microbial membrane Found on mucous membranes and in phagocytes Genetic differences in susceptibility Some hosts are genetically immune to the diseases of other hosts Particularly true of viruses Need way to attach and with intracellular pathogens a way to enter the cell - very specific

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