Chapter 15: Immunity & Body Defenses

• Chapter 15 is about Immunity

Overview of Body Defenses

• Pathogens can cause diseases in humans
• Pathogens must access a portal of entry.
• Pathogens must penetrate the surface of cells or blood.
• Pathogens must evade the body's defense.
• The body as a two broad categories of defense, innate and adaptive.
• Innate defenses lack memory, are present at birth, and are nonspecific.
• Adaptive defenses have memory, develop later in life, and are specific.
• Both innate and adaptive defenses are needed to be fully protected.
• The first line of defense consists of innate barriers.
• The second line of defense consists of the innate immune response.
• The third line of defense consists of the adaptive immune response.

Body's First Line of Defense

• The environment on the surface inhibits microbes from causing infection.
• Nutrients, temperature, and pH are factors in this environment.
• Barriers are what microbes must pass to cause disease.
• Barriers are nonspecific and are the first line of defense.
• Structural, mechanical, chemical, and genetic barriers comprise the first line of defense.

Structural Barriers

• Epithelium is found on the surface both internally and externally.
• Two types of epithelial surfaces are skin and mucous membranes.
• In both instances, the epithelium constantly undergoes mitosis and replaces sloughed layers.
• Microbes attached to the epithelium are lost.
• There are tight junctions between epithelial cells.

Mechanical Barriers

• Mechanical barriers involve movement and physically remove microbes.
• Mucociliary movement is found lining the nose and throat; microbes trapped in mucus are coughed or swallowed.
• Fluid movement, like the flow of urine, saliva, and tears, continually flushes microbes from the surface.

Chemical Barriers

• Chemical barriers are agents produced by cells on the surface.
• Keratin keeps skin dry and waterproof.
• Perspiration is secreted by sweat glands.
• Salt inhibits the growth of pathogens.
• Lysozymes are made by saliva and tears and are antibacterial.
• Sebum is secreted by sebaceous (oil) glands.
• Sebum lowers skin pH to inhibitory levels for many bacteria.
• Lowering the pH with hydrochloric acid (HCL) in the stomach has a similar effect.

Genetic Barriers

• A host can be genetically immune to diseases of other hosts.
• Microbes may lack the appropriate receptors or the ability to attack host cells.
• This specificity is referred to as species specificity.
• Examples of species specificity include HIV versus FIV and Ebola virus versus heartworms.

Normal Flora

• Normal flora can survive barriers with several adjustments to attach to the surface
• The attachement is with adhesins
• Adhesins bind to their complimentary receptor molecules
• Lock and key fit for adhesins and receptors

Practice Examples

• Salt: integument, chemical
• Lysozymes: respiratory, chemical
• Mucociliary movement: respiratory, mechanical
• HCL: digestive, chemical
• Urine: urinary, chemical
• Lactobacillus: epidermis
• Mitosis: integument, structural
• Pinworms: intestinal, genetic
• Vomiting: digestive, mechanical
• Structural barriers are in the mouth, nose, skin, intestinal, urinary, and reproductive tracts
• Chemical, mechanical, and genetic barriers are in all of the same places

The Second Line of Defense

• Occurs when pathogens penetrate the skin or mucous membranes, and get passed initial barriers.
• The second line of defense is still part of the nonspecific innate immune response.
• It consists of four components, each involved with the blood: Inflammation, Phagocytosis, Interferon, and Complement.

Inflammation

• "Itis" suffix
• Inflammation is a nonspecific response to tissue damage from various causes, such as trauma, wounds, or burns.
• The goal of inflammation is to remove the agent causing inflammation, to keep damage local, and to allow for healing.
• Inflammation is characterized by redness, heat, swelling, and pain.
• A fifth sign of inflammation is the loss of function due to pain and swelling.
• The three sequential events that occur following injury are vascular changes, edema (local), and fever (systemic).
• Vascular changes are triggered by chemicals released after an injury.
• Major chemicals include Bradykinins, Prostaglandins, Leukotrienes, and Histamine.
• Vasodilation produces redness and localized heat associated with inflammation.
• Blood-clotting proteins are delivered to the injury site, along with leukocytes.
• Edema, or swelling, can occur from some of the same chemicals that lead to increased permeability.
• There is an increased pressure due to more blood
• Swelling dilutes toxins, but can also apply pressure to nearby nerves.
• Neutrophils and monocytes are delivered to the site of infection.
• These are recruited by chemotactic factors.
• They squeeze between cells of the vessel wall and enter the site of infection with Diapedesis
• Phagocytosis occurs allowing for tissue repair and removal of pathogens (if present).

Phagocytosis

• Phagocytosis can be divided into five stages.
• Chemotaxis is the recognition of invaders due to signal molecules on the microbe surface.
• Ingestion involves membrane extensions that surround microbes, forming a phagosome.
• Fusion occurs when lysosomes fuse with the phagosome creating a phagolysosome.
• Killing involves digestive enzymes in the lysosome that destroy the microbe.
• Elimination occurs when debris is discharged out of the cell.

Fever

• 107 degree fever if microbes are present
• Fever is a systemic factor
• Results when pyrogens trigger the hypothalamus to increase the body's core temperature
• Types of pyrogens exogenous, like bacterial toxins, and endogenous, like released by phagocytes
• Fever makes the environment less hospitable for the pathogen and inhibits growth of microbe and enhance phagocytosis

Chemical Defenses

• Viruses don't reproduce on their own, they need our cells
• Chemical defenses include Interferon
• Proteins are released by host cells to nonspecifically inhibit the spread of viral infections
• It usually inhibits reproduction
• It is released by a cell onced infected to protect neighboring cells

Complement

• A chemical defense which is a Set of serum proteins designated numerically according to their order of discovery
• There are 3 primary effects:
• C3a and C5a cause inflammation
• C3b causes opsonization
• C5b-9 causes MAC/Cytoloysis
• Some microbes produce Surface Proteins that interfere with direct contact with phagocytes
• Those surface proteins can be unique however and allow for attack by the Third Line of Defense