14 Innate Immune Response

Immune System

Protects against foreign invaders (infectious diseases)

2 components:

• Innate » what you’re born with. The 1st and 2nd line of defense

• Adaptive » acquired throughout lifetime. 3rd life of defense

  • specific response to a specific pathogen

Intact skin

First line defense.

[__]: barriers that shield interior of body from outside

• Physical barrier → makes difficult to penetrate

  • prevents 99% of pathogens

• dry environment → prevents growth of microbes

• [__] continually sloughs off, along with any attached microbes

This is why damaged or open skin puts body at risk

Mucous membranes

First line defense.

[__]: barriers that line gastrointestinal, respiratory, and genitourinary tract

• bathed in antimicrobial secretions (mucus, IgA: immunoglobulin A, primary antibody)

Respiratory tract

• ciliary escalator → peristaltic pump action propels microbes away from lungs

• mucus » contains IgA

Eyes → most susceptible

• tears → cleansing; contains lysozyme and IgA

• undergoes blinking from constant motion

Urogenital tract

• urine → cleanses urethra

• has secretions

GI tract

• gastric acid acts in stomach

• normal flora compete with pathogens in intestine

antimicrobial defenses

First line of defense.

[__] protect skin and mucous membranes

eg.

• sweat: salt on skin

• lysozyme → degrades peptidoglycan

  • found in tears, saliva, blood and phagocytes

• lactoferrin: iron-binding proteins → sequesters/isolates iron

  • found in saliva, blood, mucus, and tissue fluids

normal microbiota

First line defense.[__] or human microbiome are the microorganisms found on the body surfaces; normally do not harm host.

Stimulates the host immune response

Provides significant protection against invasion by:

• competitive exclusion

» physical exclusion → takes up space and covers binding sites so pathogens can’t bind

» competing for nutrients → makes nutrients unavailable for pathogens

• producing chemicals (bacteriocins, acids) toxic to invaders

immune system

Cells of the [__] are always found in the normal blood

→ numbers increase during infection

→ includes white blood cells (WBCs); also known as leukocytes » very important in host defenses

Neutrophil

Most abundant leukocyte (55-85% of WBC)

• increases in number during infection

• eats and kills pathogens (phagocytosis)

Basophils

Leukocyte involved in allergic reactions and inflammation

eg. mast cells: cells similar to [__] of the blood, except they are found in tissues

Eosinophils

Leukocyte responsible for fighting parasitic worms.

Done by poking holes in their membranes

Macrophages

Cells that differentiate from the leukocyte, monocyte. Involved in phagocytosis

• present in most tissues

• abundant in liver, spleen, lymph nodes, lungs, and peritoneal cavity

Dendritic cells

Cells that differentiate from the leukocyte, monocyte. They are branched cells

• sentinel cells → function as “scouts”

  • has pseudopods that grab onto and engulf the pathogen in tissue and bring it to cells of the adaptive immune system for “inspection”

• found in the liver, spine, lung, and spleen

Lymphocytes

Leukocyte involved in adaptive immunity

• has specific response to antigen (pathogen) with production of antibodies

• B-cells » produce antibodies to specific antigens

• T cells differentiate into (3) kinds of cells:

  • Cytotoxic T cells → destroy infected cells

  • Helper T cells → recruit B and T cells to site of infection

  • Natural Killer cells → kills abnormal cells, even host cells

Complement System

System composed of a group of proteins circulating in blood and fluids. Named [__], as it “complements” the function of antibodies

When activated, leads to protective outcomes:

• inflammation

• opsonization: coating of an object with molecules for which phagocytes have receptors → makes it easier for phagocyte to engulf object

• cytolysis → lysis of foreign cells

  • spontaneous assembly of system proteins in doughnut-shaped structures known as membrane attack complexes (MAC) → creates pores in cell → lyse

phagocytosis

Carried out by phagocytes

The act of engulfing and digesting microbes and cellular debris

inflammatory response

Occurs in response to microbial invasion or tissue damage.

4 Cardinal signs:

• heat

• pain

• redness

• swelling

in addition to loss of function

[__] is done in order to contain damage, localize response, eliminate invader, and restore tissue function.

• initiated by chemical mediators released by cells around damage

  • leads to dilation of blood vessels → increased blood flow to area

  • diapedesis: migration of leukocytes and phagocytes from blood vessels into tissue

Outcomes of inflammation are:

• limited damage and restored function

• damage, as inflammation itself can cause damage

  • severe consequences in delicate systems

  • inflammation around the brain and spinal cord can lead to meningitis or encephalitis

Apoptosis

Programmed cell death. Cells die without eliciting an inflammatory response → cell undergoes changes to signal destruction by macrophages

Fever

An increase in internal body temperature to 37.8C or higher

• strong indicator of infection, especially of bacterial infection

• higher temperature for bacterial than viral infections

  • caused by pyrogens: fever-inducing substances

  • eg. lipid A of Gram-negative bacteria

Has a curative effect

» inhibits the growth of or kills pathogens

» speeds up body’s defenses