Exam 3 – Non-Specific Host Defenses (Native Immunity)

What are the two parts of the immune system and where do they come in the line of defense?

• innate (nonspecific) – 1st line of defense

• adaptive (specific) – 2nd line of defense – protects/re-exposure

Specific (adaptive) defenses

• respond to particular agents

• antibodies, specific cells

Nonspecific (innate - “born with”) defenses

• respond to all invaders 

• first line of defense

• basic ability to keep almost everything out

• they include

  • physical barriers

  • chemical barriers

  • cellular defenses

  • inflammation

  • fever

What is the largest organ of the human body an an excellent physical barrier to microorganisms? And the worst thing to do to it?

• skin

• damage it on purpose – tattoos, piercings – go to a hygienic, professional place if you get these done

Physical barriers to infection

• skin

• mucous membranes

• hair

• many “symptoms” are actually physical barriers

  • mucus

  • coughing and sneezing

  • vomiting and diarrhea

Chemical barriers to infection

• lysozyme

  • saliva, tears, mucus

• salt

  • sweat

• acid

  • gastric juices

  • sweat

  • sebum

Cellular defenses to infection

• blood

  • ~60% plasma/serum (liquid)

  • ~40% formed elements

• formed elements

  • red blood cells (erythrocytes) – RBC

  • platelets (not cells)

  • white blood cells (leukocytes) – WBC

Types of leukocytes (white blood cells)

• myeloid

  • basophils – release histamine

  • mast cells – release histamine

  • eosinophils – increase in allergic reaction

  • neutrophils

    • phagocytic

  • monocytes and macrophages

    • phagocytic

• lymphoid

  • lymphocytes – specific defenses

Cellular defenses – phagocytosis (intracellular killing) – what cells are involved?

neutrophils and macrophages

Cellular defenses – phagocytosis (intracellular killing) – what are the steps in phagocytosis?

• chemotaxis – specific chemicals, cytokines

• adherence and ingestion

• digestion

Cellular defenses – phagocytosis (intracellular killing) – does it kill all microbes?

• no

• some microbes have evolved to specifically resist phagocytosis at any one of these steps

Neutrophil

• phagocytic

• “first on the scene”

• live only a day or two

• high number in blood count suggests infection

Macrophage – “big eater”

• can be "fixed” or “wandering”

• live for months 

• also involved with specific defenses 

• more of these are in our tissues 

Steps in phagocytosis

• the macrophage attaches to a bacterium

• pseudopodia then surround the bacterium

• the pseudopodia bring the bacterium into the cytoplasm of the macrophage, where union with lysosomes takes place

• within the newly formed phagolysosome, the bacterium disintegrates through the activity of lysosomal enzymes

• the process concludes with the elimination of bacterial debris during egestion

Bacterial resistance to phagocytosis

• some bacteria secrete leukocidins that killleukocytes (dead WBCs become pus)

  • pyogenic – pus forming

  • S. aureus and S. pyogenes

• Some bacteria can form a capsule that prevents adherence

What is inflammation?

• body’s defense response to tissue damage

  • infection and/or mechanical injury (damage)

• characteristics (cardinal signs)

  • calor – increase in temperature

  • rubor – redness

  • tumor – swelling

  • dolor – pain

What is an acute inflammatory response?

• short-term (days)

• three major steps

  • kill invaders

  • clear debris

  • repair tissue

• histamine released

• vasodilation – increased blood flow/warmth

• edema – fluids accumulate

• pus – accumulation of dead cells, microbes and tissue debris

  • pyogenic bacteria induce pus formation 

What is systemic inflammation?

• no longer localized

  • systemic infection

• can lead to septic shock

  • high fever 

  • massive efflux of fluids

  • loss of blood pressure and volume

What is chronic inflammation?

• no clear winner between invader and host

• primarily macrophages involved

• host defense system may attempt to confine invader

  • formation of granulomas

• tuberculosis and rheumatoid arthritis are also forms of chronic inflammation

What is a fever?

• anything above 100.5ºF

• body’s thermostat gets reset in response to pathogen – pyrogens released (vs. pygoens – pus forming)

• antipyretics – fever reducing drugs

• benefits of fever

  • slow growth of pathogens 

  • microbial toxins may be inactivated

  • increases immune response

  • patient feels ill