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Components of Adaptive Immune System (Innate Immune System (Detecting…
Components of Adaptive Immune System
Reasons for Adaptive Immunity
Intracellular viruses + bacteria hide from innate immunity
Need memory for specific antigens
Microbes evade innate immunity
Characteristics
Delayed response
Immunological memory
Specific acquired immunity
Requires antibodies and T+B lymphocytes
Innate Immune System
Resistance is not improved by repeat infection
Independent of lymphocytes
Rapid response
1st line of defence
Non-specific
Present from birth
No immunological memory
Physical barriers: skin, sebum, mucous membranes
Physiological barrier: Pyrexia to inhibit microbe growth
Chemical barrier: Gastric acidity kills microbes
Phagocytic cells: neutrophils + macrophages
Detecting microbes
PRR: pattern recognition receptor - a family of proteins which recognise and bind to a variety of pathogen ligands
Circulating PRRs include antimicrobial peptides, lectins, collectins
PAMP: pathogen associated molecular pattern e.g. lipopolysaccharide
this is how microbes are recognised
Cell associated PRRs =
Toll like receptors
Nod like receptors
Rig like helicase receptors
Neutrophils
Life span: 6 hours -12 days
Has 2 main granules:
Primary lysosomes - Combine with phagosomes containing microbes to digest them
Secondary granules
Important role in innate immunity by phagocytosis
Granules have Fc and complement receptors
Polymorphonuclear leukocyte
65% of blood
Monocytes
Life span: months
Phagocytosis in innate immunity
5% of blood
Presents antigens in adaptive immunity
Mononuclear leukocyte
Differentiates into macrophages in the tissues
Has Fc, complement, PRR, toll-like and mannose receptors - can bind to loads of types of microbe
Has lysosomes containing peroxidase to kill microbes
Macrophages
Presents antigens to T cells in adaptive immunity
First line of non-self recognition
Phagocytosis in innate immunity
Has lysosomes containing peroxidase
Life span: months/years
Has Fc, complement, PRR, toll-like and mannose receptors - can bind to loads of types of microbe
Examples: Kupffer cells, microglia
Eosinophil
Life span: 8-12 days
5% of blood
Associated with parasitic infections and allergic reactions
Granules contain major basic protein (MBP) which activates neutrophils, provokes bronchospasm and induces histamine release from mast cells
Polymorphonuclear leukocyte
Granules stain for eosin - show up red/pink
Basophil
Lifespan: 2 days
Associated with parasitic infections and allergic reactions
2% of blood
Express high affinity IgE receptors
Polymorphonuclear leukocyte
Binding of IgE to receptor causes de-granulation which releases histamine
Similar to mast cells however mast cells are fixed in tissue and basophils are able to circulate in blood around the body
Mast Cell
Binding of IgE to receptor causes de-granulation which releases histamine
Express high affinity IgE receptors
Only found in tissues, produced in bone marrow
C-kit protein is needed for development
T Lymphocytes
Lifespan: hours - years
Matures in thymus, originates in bone marrow
10% of blood
Major role in adaptive immunity
Mononuclear leukocyte
Recognises antigen displayed by antigen presenting cells - cannot recognise soluble antigens
Found in blood, spleen and lymph nodes
T cell receptors recognise foreign antigens with the major histocompatibility complex (MHC)
There are 4 types of T cell
T Helper 2
Helps B cells make antibodies
Activates macrophages and natural killer cells
CD4 - Extracellular pathogens
Produces IL-4, -5, -6, -10, -13
T Killer (cytotoxic)
Kills cells directly
CD8
Induces apoptosis
T Helper 1
Helps B cells make antibodies
Activates macrophages and natural killer cells
CD4 - Intracellular pathogens
Produces IL-2, gamma-interferon and TNF beta
T Reg
Regulates immune response
B Lymphocytes
Lifespan: Hours - years
Major role in adaptive immunity
15% of blood
Originate and mature in bone marrow
Mononuclear leukocyte
Recognise antigen displayed by antigen presenting cells
Express antibody on their surface
Differentiates into
plasma cells
(make antibodies) and
memory cells
Natural Killer Cells
Found in spleen + tissues
Kills virus infected cells and tumour cells by apoptosis
Expresses CD56
Dendritic Cells
Induces primary response in dormant T cells
Found in tissue with contact to outside environment e.g. skin, linings of nose, lungs and stomach
Antigen presenting cells
Major Histocompatibility Protein
Class I: Expressed by all nucleated cells and displays antigen to cytotoxic T cells
Class II: Expressed by macrophages, dendritic cells, B cells. Displays antigen to T helper cells
Initiates T cell response
MHC protein acts as a safety mechanism - it prevents immune system from being activated too easily as T cells only react to the antigen if it is presented within a MHC complex
Encoded on chromosome 6