A&P: CH.21 [Immune System]

• immunity: resistance to disease
• innate immunity: nonspecific, generalized defense mechanisms that are present at birth; fast

  • surface barriers (skin etc.)
  • internal defenses (phagocytes, etc)
• adaptive (acquired) immunity: specific defenses against pathogens acquired during life; slower

  • B cells (humoral immunity)
  • T cells (cellular immunity)
• inflammation is the body's response to injury or infection; it involves redness, swelling, heat, pain, and loss of function
• innate and adaptive defense similarities

  • same defensive molecules
  • specific pathways to target certain foreign substances
  • proteins released during innate responses alert cells of adaptive system
• the skin provides an initial barrier to entry by microorganisms; keratin is also resistant to most weak acids and bases and to bacterial enzymes and toxins
• skin also has protective chemicals like

  • acid: acid mantle which inhibits bacterial growth
  • enzymes: lysosomes
  • mucin: traps microorganisms
  • defensins: antimicrobial peptides
  • others: lipids in sebum and dermcidin in eccrine sweat toxic to bacteria
• respiratory tract mucosae have structural modifications to prevent pathogens from entering
• internal innate defenses include phagocytes, natural killer cells, antimicrobial proteins and fever
• neutrophils are short-lived white blood cells that engulf and digest bacteria
• macrophages are large white blood cells that can ingest and destroy many types of pathogens
• natural killer (NK) cells destroy virus infected host cells and cancerous cells
• opsonization: pathogen is coated with opsonins to accelerate phagocytosis
• NK cells eliminated cancer sells by detecting general abnormalities such as lack of "self" cell-surface proteins called MHC
• inflammatory response benefits

  • prevents spread of damaging agents to nearby tissues
  • disposes of cell debris and pathogens
  • alerts adaptive immune system
  • sets stage for repair
• histamine: a compound which is released by cells in response to injury and in allergic and inflammatory reactions, causing contraction of smooth muscle and dilation of capillaries.
• toll-like receptors: a type of receptor that recognizes pathogen-associated molecular patterns; releases inflammatory chemicals called cytokines
• hyperemia occurs when the blood vessels dilate and the blood flow increases; responsible for redness and heat during inflammation
• exudate: a mass of cells and fluid that has seeped out of blood vessels or an organ, especially in inflammation; contributes to pain and swelling
• phagocytes mobilization

  1. leukocytosis: neutrophils enter blood from bone marrow
  2. margination: neutrophils cling to capillary wall
  3. diapedesis: neutrophils flatten and squeeze out of capillaries
  4. chemotaxis: neutrophils follow chemical trail from inflamed site
• antimicrobial proteins enhance innate defenses by attacking microorganisms by directly hindering ability to reproduce; most important are interferons and complement proteins
• interferons: help protect cells that have not yet been infected by viruses; cancer fighting cells like macrophages and NK cells
• IFN alpha and beta have antiviral effects and activate NK cells
• IFN gamma "immune interferon" secreted by lymphocytes and activated macrophages
• IFNs can treat hepatitis C, genital warts, multiple sclerosis and hairy cell leukemia
• complement system has three functions: opsonize (coat) pathogen so phagocyte will engulf it, lyse (burst open) pathogen membrane, attract immune cells to the area
• complement is a nonspecific defensive mech. but it enhances both innate and adaptive defenses
• classical pathway: antibodies bind to an antigen on a microbe's surface which activates the first enzyme in the cascade; adaptive immune system
• lectin pathway: lectins bind to carbohydrates on the surface of pathogen; innate immune system
• alternative pathway: activated spontaneously when other complement factors interact; lack complement activation inhibitors our own cell have
• classical, lectin, alternative pathway converge at C3, which cleaves into C3a and C3b -> enhances inflammation, promotes phagocytosis, cause cell lysis
• MAC (membrane attack complex): a complex of enzymes that digests the bacterial cell wall leading to cell lysis
• C3b molecules are responsible for opsonization of bacteria and phagocytosis
• leukocytes and macrophages exposed to foreign substances release pyrogens that act on clusters of neurons in the hypothalamus- leading to fever
• fever is an adaptive response because it increases metabolic rate, slows growth of microbes, and stimulates production of antibodies
• adaptive immune system: body's built-in specific defensive system that eliminates pathogens; must meet or be primed with an antigen
• adaptive system amplifies inflammatory response and responsible for complement activation
• AIDS and cancer appears when adaptive immune system is not working properly.
• humoral immunity: antibodies present in body's fluids; produced by lymphocytes and bind to extracellular targets to inactivate them temporarily and mark them for destruction by phagocytes or complement
• cellular immunity: lymphocytes themselves instead of antibodies defend body; cellular targets are parasite-infected tissues, cancer, foreign graft cells

  • direct: killing infected cells
  • indirect: release chemicals enhancing inflammatory responses