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THREE LEVELS OF DEFENCE (:STAR:LEVEL 2:STAR:
Innate immune response
Non…
THREE LEVELS OF DEFENCE
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:STAR:LEVEL 2:STAR:
Innate immune response
Non-specific: General defences to attack anything that doesn’t belong
Lymphatic System
Tissue/Interstitial Fluid: Bathes the tissues and cells – supplying them with nutrients and O2, and removes wastes
• Some tissue fluid returns directly into the capillaries, but some drains back into the blood circulation through a network of lymphatic vessels -> Called Lymph and contains Leucocytes (WBC), pathogens and cell debris.
Lymphatic System – Role
- Returns proteins that leak out of the blood, back into the blood
- Role in defence (continuous movement of WBC allow for routine screen of body for foreign material)
Lymphatic Vessels: Transport lymph
• Relies on muscle contraction and backflow prevented by valves)
Lymph nodes: Clumps of lymph tissue at particular locations
• Filters Lymph. Traps foreign particles in fibres – these can then be dealt with
Spleen: Stores and releases blood, destroys blood-borne pathogens
Tonsils: Lymph tissue at the back of the throat, ideal spot to combat pathogens
Thymus gland: Near heart, T Lymphocyte maturation
Bone Marrow: Generation of B & T Lymphocytes
White Blood Cells
- Called Leukocytes
- Manufactured in the Bone Marrow
- Possess a nucleus
Inflammation
• Complex process involving many different cell types and signalling molecules
• Swelling, redness, heat and pain
• Triggered in two main ways: Macrophage initiated and Cell damage initiated
Macrophage initiated
• White blood cells (WBC) (macrophages or dendritic cells) are strategically distributed throughout all body tissues, particularly skin, lymph, lungs, liver, spleen and kidneys
• Act as sentinels to check everything passing by
• Engulf foreign material and produce signalling molecules
called cytokines
• Different cytokines depending on job: These include interferons and interleukins
Cell damage initiated
• Mast cells can be stimulated by ruptured body cells and release histamine, as can circulating WBC called basophils
• Histamine: promotes vasodilation in tissues (increases blood flow) and Increases permeability of capillaries so WBC can squeeze out to intracellular fluid more easily
• When activated, WBC (leukocytes) migrate into the region due to chemotaxis (following the source of the chemical signalling molecules)
• Leukocytes (monocytes and neutrophils) come to area and phagocytose foreign material
• Neutrophils are short lived and die in a few days to prevent the risk of being infected and spreading disease around body (This is why infected sites often accumulate pus- dead neutrophils)
• Not all bacteria are killed as some have evolved ways to escape phagocyte
Distinguishing self from non-self
• Foreign molecules on either the outer surface of invaders or the toxins or enzymes they secrete alert general defences
• Even parts of a protein or a small toxin molecule can be enough to trigger an immune response
• Anything that triggers an immune response is an antigen
• These general defences identify non-self molecules that are characteristic of microbes but not host cells
• These can include:
• Peptidoglycan ,Chitin and Specific Protein sequences (eg, those found in the flagella)
• More specific recognition (for a particular disease) can also occur (see level 3 for more detail)
Innate responses
• Work for any disease/invader regardless of type
• Not something learnt (past experience will not change response for next time)
• Similar in both plants and animals
Fever and Pain
• Some interleukins released by macrophages signal to hypothalamus (temperature regulator in brain)
• Hypothalamus resets body temperature to higher than normal (eg 39oC)
• This can restrict the functioning and reproduction of many pathogens (above optimum temperatures for their enzymes)
• Some cytokines also cause drowsiness (lets body save energy for fighting invaders and repairing damaged tissue)
Complement
• Approx 20 different kinds of small proteins involved in inflammation
• Activated when they encounter a foreign body, eg bacteria
• Act by:
a. Binding to surface of bacteria and yeast to tag for detection and uptake by phagocytes
b. Inducing chemotaxis
c. Stimulate mast cells to release histamine
d. Membrane attack complex - form a structure to puncture membranes
Interferons
• Released by virus infected cells
• Act as warning signal from doomed cell to neighbours
• Neighbours cause changes in surface of surrounding cells to help prevent infection and inducing virus resistance genes to be expressed
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