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January 18, 2013
Host defenses Part I
Humans are difficult environments for newly introduced microorganism
Kind of like old pioneer movie
Many kinds of obstacles and barriers
Physical barriers:
Skin-covers most of exposed areas
Skin cells die and slough off
Mucus-covers majority of respiratory and GI tracts
Helps prevent bacterial interaction with host cells
Mechanical defenses:
Ciliary escalator: Moves microorganisms out of area
Most important in respiratory tract
Can be damaged by smoking, disease or trauma
Urine flow
Makes pathogens fight against flow of liquid
Coughing, sneezing and peristalsis
Muscles work to move irritants out
Chemical defenses:
Lysozyme
Enzyme in tears and mucus that degrades bacterial cell walls
Very important for protection of eyes
Stomach acid
Low pH conditions prevent most bacteria from persisting in
stomach
Most GI pathogens have temporary means to survive low pH
Competition
Normal Flora
Crowded restaurant model
Normal flora often important for good health
Normal Flora not found in all systems
Lower respiratory, upper urinary, CNS, blood are typically
sterile or nearly sterile with a small number of microbes being
cleared.
Immune responses:
Broken down to two types of response
Humoral response
Involves B-cells, antibodies and complement
Cellular immune response
T-cells are main player
Definitions:
Cytokine-soluble molecule that helps regulate immune functions.
TNF, IL-I, IL-6, IL-10 etc.
Inflammation-host immune response that is includes increased localized
temperature, increased permeability of the capillaries, increased blood flow.
Leukocyte-any "white blood cell"
Lymphocytes-T-cells and B-cells
PMN's=polymorphonuclear luekocytes-includes neutrophils, eosinophils
and basophils
Mononuclear cells-includes lymphocytes, monocytes and macrophages
Immune response and disease:
Many of the symptoms associated with microbial infection are caused
by host immune response
Fever, inflammation, change in blood pressure
We are now beginning to examine if it is best to treat symptoms or not
Fever plays an important role in host defense
Many NSAI drugs block fever and inflammation
Many new treatments allow body to do its part