Body's Defense Overview

Overview of Body Defenses

• Pathogens can cause disease in humans
• Pathogens must access a portal of entry to cause disease
• Pathogens must also penetrate the surface and evade the body's defense
• The body has two broad categories of defense, Innate and Adaptive
• Innate defense does not have memory and is nonspecific and present at birth
• Adaptive defense has memory and is specific
• Innate and Adaptive defenses happen at the same time to be fully protective
• The body has 3 lines of defense:
  • First line is Innate barriers
  • Second line is Innate Immune Response
  • Third line is Adaptive Immune Response

The Body's First Line of Defense

• The environment inhibits on the surface inhibit microbes from causing infection
• Barriers are nonspecific and serve as the first line of defense
• These are barriers to prevent microbes causing disease
• Nutrients, temp, pH etc are barriers
• Structural barriers are a type of the first line of defense
• Epithelium is found on the surface both internally and externally
• Skin and Mucous Membranes are the two types of epithelial surfaces
• The epithelium is constantly undergoing mitosis, replacing layers that are sloughed
• Microbes attached to the epithelium are lost
• There are tight junctions between epithelial cells
• Mechanical barriers physically remove microbes, and involve movement
• Mucociliary movement is found lining nose and throat
  • Microbes are trapped in mucus and then cilia bring it up to be coughed/swallowed
• Fluid movement is when the flow of urine/saliva/tears helps continually flush microbes from the surface
• Chemical barriers are Agents produced by the cells on the surface
• Keratin keeps the skin dry, waterproofs the skin
• Perspiration is secreted by sweat glands and the salt inhibits the growth of pathogens
• Lysozymes are made by saliva and tears and are antibacterial
• Sebum is secreted by sebaceous (oil) glands and lowers skin pH to a level inhibitory to many bacteria
  • Lowering the pH to be HCL in the stomach is a chemical barrier
• Genetic barriers are when;
• Host is genetically immune to diseases of other hosts
• Microbe doesn't have the appropriate receptors or the ability to attack host cells
• Lack of receptors is also known as Species Specificity
  • Examples are: HIV versus FIV, Ebola virus, and Heartworms
• Normal flora survives these barriers because they have adjustments to attach/adhere to the surface
• Attachment is with Adhesins
• Adhesins bind to their complementary receptor molecules with lock and key type fit

Practice Examples

• Salt is integument/chemical barrier
• Lysozymes are respiratory/Chemical barrier
• Mucociliary movement is a respiratory/mechanical barrier
• HCL is a digestive/chemical barrier
• Urine is a urinary/chemical barrier
• Mitosis is a intestinal/structural barrier
• Pinworms is a intestinal/genetic barrier
• Vomiting is a digestive mechanical barrier
• Structural barriers location: Mouth, Nose, Skin, Intestinal tract, Urinary tract, Reproductive tract

The Body's Second Line of Defense

• The second line of defense occurs when pathogens penetrate the skin or mucous membranes
• The second line of defense is nonspecific, and is still part of the innate immune response
• The second line of defense Consists of 4 components which each has some involvement with the blood:
  • Inflammation
  • Phagocytosis
  • Interferon
  • Complement
• Inflammation "itis" is a Nonspecific response to tissue damage from various causes (trauma, wound, burn)
• The goals of inflamation is to remove agent causing inflammation, to keep damage local, and allow for healing to occur
• Inflammation is Characterized by redness, heat, swelling, and pain
• 5th sign of inflammation is the loss of function (pain/swelling)
• Following injury there are 3 sequential events in Inflammation:
  • Vascular changes
  • Edema (local)
  • Fever (systemic)
• Vascular changes occur when many chemicals are released triggering dilation
  • Bradykinins, Prostaglandins, and Histamine trigger dilation
• Vasodilation produces redness and localized heat associated with inflammation
• Vascular changes also Delivers blood clotting proteins to site of injury as well as leukocytes
• Edema (swelling) occurs when some of the same chemicals lead to increased permeability, and increased pressure due to more blood
• Swelling dilutes toxins
• Swelling applies pressure to nearby nerves
• During Inflammation, the combonation of Neutrophils and monocytes are delivered to the site of infection
  • Neutrophils and monocytes are Recruited by chemotactic factors
    • Squeeze between cells of vessel wall and enter site of infection, this is Diapedesis
  • Phagocytosis occurs allowing for tissue repair and removal of pathogen (if present)
• Phagocytosis is a process where Cells capable of phagocytosis engulf foreign material
  • The Process can be divided into five stages:
  • Chemotaxis- recognition of invader due to signal molecules on the microbe surface
  • Ingestion- membrane extensions surround microbe forming a phagosome
  • Fusion- lysosome fuses with phagosome creating a phagolysosome
  • Killing- digestive enzymes in lysosome destroy microbe
  • Elimination- debris discharged out of cell
• Fever is a Systemic factor that only occurs if microbe is present
• Fever results when pyrogens trigger the hypothalamus to increase the body's core temperature
  • Has an impact on the Prostal gland in the brain
• There are Various types of pyrogens
  • Bacterial toxins (exogenous)
  • Released by phagocytes (endogenous)
• Fever makes environment less hospitable for the pathogen (inhibit growth of microbe, enhance phagocytosis)
• Chemical Defenses use interferon, which is protein molecules released by host cells to nonspecifically inhibit the spread of viral infections
• Interferon Usually works by inhibiting reproduction of the virus
• Interferon is Released by a cell once infected to protect neighboring cells
• Chemical Defenses use complement
• Complement is a Set of serum proteins designated numerically according to their order of discovery
• Complement will have 3 primary effects:
  • Inflammation
  • Opsonization
  • MAC/Cytolysis
• Some microbes produce surface proteins that interfere with direct contact with phagocytes (either due to similarity to host or by blocking receptors)
• These surface proteins can be unique however and allow for attack by the Third Line of Defense