Innate community

Purpose of immune system

To protect the host from infectious pathogens

Where can pathogens be found

In various compartments of the body where they must be combated by different host-defensive mechanisms

How does the immune system accomplish this when faced with an enormous diversity of potentially infectious microorganism?

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What is the first line of defense: The physical and chemical barriers

Skin (desquamtion)

Lungs (Surfacent)

blood-brain barrier ensures microbes cannot enter the barriers

Liver (Bile acids) ensure chemicals destroy pathogens

Eyes (tears) contain lysozymes which

Stomach (gastric acids)

Digestive tract

nasopharynx

Chemical factors

Low pH (3-5) of skin

Lysozyme in tears,saliva and urine

Low pH (1.2-3.0) of gastric juice

Low pH (3-5) of vaginal secretions

what does lysozymes digest

Lysozymes digests the cell walls of gram-positive and gram-negative bacteria

Lysozymes are more effective against gram positive bacteria because there are less cell wall layers so it is easier to break down

Defensins

Defensins are Amphipathic peptides containing a short chain of amino acids which have 2 different characteristics-one is hydrophobic and the other is hydrophilic so each separate on different sides of the molecule

Epithelial barriers against infection

The physical-mechanical (intact epithelial surface, longitudical flow of air or fluid, movements of mucous from cilia)

chemical (skin-fatty acids, enzymes- kysozymes in saliva and tears, pepsin in the gut, low pH, anti-bacterial peptides

microbiologicl (commensal bacteria- competition for nutrients, blocking of adhesion, production of anti-microbial substances)

Functions of epithelia in an innate immunity (immune system 1st line of defence

There is a physical barrier to the infection so pathogens cannot pass through

Antibiotics are produced to destroy and kill microbes

Intraepithelial lymphocytes kill microbes and infected cells

What happens if pathogems breach and the mechanical barrier and enter the underlying tissue

An infection occurs

The 2nd line of defence: cellular and soluble factors

Phagocytic cells: monocytes/macrophages, neutrafils

Natural killer (NK) cells

Cell surface receptors

complement system

cytokines

other soluble factors

Development of myeloid cells

stem cells are produced in the bone marrow

Inflammation

tissue reaction which delivers mediators of host defense- circulating cells and proteins to the sites of infection and tissue damage

Functions of NK cells

They have cytoplasmic granules: contains perforin and granzymes- involved in cell-mediated cytotoxicity/ programmed cell death