Immune system

Immune system

1. Against infections

   • Innate
     • -work within minutes after a pathogen invasion
     • Characteristics
       • less specificity
         • general, attack pathogens
       • Fast responses
         • not require time to develop
       • Required receptors
         • recognize pathogen-associated molecular patterns(PAMP)
     • Mechanisms/Actions
       • 1. phylogenetically order 2. exist before or react immediately after contact with pathogen(no memory) 3.react predominantly to infectious agents 4.First line defense 5.stimulate and shape adaptive immunity
       • Phagocytosis(major)
       • Antigen-recognition
         • Responsible by NK cells
           • 1. no antigen receptors 2. have surface receptors that inhibit killing function: -Kill inhibitory receptor(KIR):recognize abnormal levels of MHC class I(normal : NK cells do not kill it ; lower amounts(usually the indicator of infected cells/tumor cells): will be killed) 
           • The importsnce
             • 1. Viral can interfere with the expression of MHC-avoid the killing by CD8+ T  cells: NK cells are important for catching these infected cells
     • Cells and functions
       • Mast cells
         • 1. inflammation
       • Monocytes/Macrophages
         • 1 Phagocytosis 2.inflammation 3.T-cell activation 4.Tissue repair
       • Neutrophils
         • 1. Phagocytosis 2. Inflammation
       • Neutral Killer cells
         • 1.Killing of infected or tumor cells(through detect the amount of MHC I) 2.Activation of Macrophages(by IFN-y)
       • Eosinophils
         • 1. Defense against parasite
       • Dendritic cells
         • 1. Phagocytosis 2. Activation of Naive T-cells
   • Adaptive
     • -take times for the responses to a specific pathogens with memory -Highly specific -it work when the innate immunity cannot control and eliminate the pathogen. -with the ability to form "memory' of the pathogen -Quickly response: the organism is infected with the same pathogen
     • Cells
       • B and T lymphocytes
         • 1. Have surface proteins(antigen receptors): recognize only one antigen 2. T cells: responsible for one small peptide 3. B cell: responsible for more than just a small peptide once the antigen binds the receptor of B cell/Tcell, they are activated and triggers an immune response.
     • Mechanism/reaction
       • Antigen recognition
         • The formation of recptors
           • combine conserved areas of receptor
             • with variable gene segments 1. recombining DNA 2. DNA mutation
         • Differences between T and B cell receptors
           • Structure: BCR:Divalent TCR: monovalent
           • Target antigen
             • B cells : antigen in native form T cells :only recognize antigen fragments with epitope size
           • Need assistant
             • B cells : does not need help from other cells to recognize antigen T cells: only recognize peptides in the presence of MHC (a surface protein)-antigen has to go through antigen processing
           • restriction*
             • T cells : MHC restricted and hiscompatible to be activated
             • MHC
               • -Highly variable proteins:that allow the immune system to recognize self from non-self -also know as HLA(human leukocyte antigen)(CLASS II):type individuals for BM and organs transplates -inherited one set of Class I(A,B,C) and Class II(HLA-DR,DP,DQ) from each parent(expressed equally).
               • Types
                 • MHC class I
                   • 1.expressed on all nucleated cells 2. responsible for graft rejection 3. MHC I must be expressed/by target cells to be killed by an antigen-specific CD8+ T cells
                 • MHC class II
                   • 1. expressed by immune cells(macrophages,dendritic cells, T cells and B cells)

2. Cells

   • Granular
     • -derived from Myeloid stem cell
     • Eosinophil
     • Basophil
     • Neutrophil
       • 1.contains granules 2. CD66 membrane marker protein
   • Agranular
     • Lymphocytes
       • -T cells -B cells -NK cells
       • T cells
       • B cells
       • Nature-killer cells
         • 1. used in experiment:to test the ability of lymphocytes to kill specific target cells 
     • Monocytes(Macrophage)
       • 1. Macrophage=Large,eating      -Lysosomes      -CD14 membrane marker protein 2.Function:-ingest and eliminate infectious agent-regulate other immune cells(both innate/adaptive)
     • Plasma cell
       • -differentiated from B Lymphocyte
     • Dendritic cell
       • 1.reside in tissue in an immature form: -mature when an infection/injury occurs 2.The role of mature DC: -travel to the lymphoid organs with antigen on their surface(antigen-presenting cells) -can present the antigen on the surface of T-cells

3. Front Line of Host Defense(Part of innate immunity)

   • Skin
     • Epithelia
       • Chemical barrier
       • Intraepithelial lymphocytes
       • Normal bacterial flora
       • Physical barrier
   • Gut
   • Lungs
   • Eyes/nose

4. Charateristics

   • Discriminate self & non-self
   • Memory
     • -allow the immune system to react more quickly and effectively to a stimulus that has encountered before.
   • Specificity
     • respond to the pathogen that is at hand