IMMUNITY

Nota:

• -slow  - first line of defence 

1. Physical Barrier
   1. skin
   2. mucous membrane
   3. natural flora
   4. Natural secretion
2. Stages of infection
   1. Adherence of pathogen
   2. Penetration of epithilium
   3. Local infection of the tissue

1. Stages of infection
   1. lymphatic spread
   2. Adaptive immunity
2. Lymphocytes : Cells with receptors that are highly specific
   1. Cell mediated Tcells
      1. originate in bone marrow but mature in thymus and found tissue and blood
      2. Naieve Tcell
         1. CD4+
         2. CD8
   2. Humoral Bcells
      1. cells origniate and develop in the bone marrow
      2. Naieve Bcell

         Nota:

         •  Activated when the antibody on the B cell recognises an antigen through contact with epitome  engulfs it and presents it throgugh an MHC CLASS 2 - helper T cell then comes along rtecognises it and assist B cells to differenciate 
         1. Plasma Cells
            1. Antibodies
               1. Structure

                  Nota:

                  • Composed to two heavy chains , two domains and two chains.  Has a variable domain and constant domain  Light chain and heavy chain ' Fc regioin binds to other cell Fab regions binds to antigen 
               2. Function
                  1. Neutralisation

                     Nota:

                     •  Neutralization o Bind to the surface of pathogen o Prevents adherence or infection of host cells
                  2. Oponisation

                     Nota:

                     • 1q binds to a platform created by hexameric IgG  This produces inflammatory mediators, which produce opsonins  Production of opsonins o Opsonins bind to antigen o Enhanced clearance by phagocytes that recognise the Fc portion of the antibody o Opsonisation is the alteration of the surface of the pathogen/particle that increases the rate at which it is phagocytosed  Deposition of pore forming protein
                  3. Lysis

                     Nota:

                     •  Complement mediated lysis of cells that are coated by antibody (particularly IgM and IgG)  Complement is a series of serum proteins that interact with each other in a cascade. Important role in responses to bacteria and viruses.
                  4. Antibody dependent cellular toxicity

                     Nota:

                     • Antibody dependent cellular cytotoxicity  Cells such as NK cells can kill cells that are coated by antibody  NK cells will not kill free antigen  Limited to viral infection – Cant kill antibody coated bacteria 
               3. diversity

                  Nota:

                  • The diversity comes from the splicing that occurs with the genes.  Heavy chain is encoded by VDJC and  Light chain is encoded by VJC recombination creates unique antibodies per cell  Rearrangment VH3DH7JH5 = all matieral b/w v3 to d7 is deleted along with matieral b/w d7 to h5 all the matieral upstream and downstream kept 
               4. Types

                  Nota:

                  • Variation in heavy chain constant regioin detemines isotype  Intially make IgM in naieve cells but then upon maturation make isotypes throgyuh class swithching  as the variable regions remainsthe same the specifiicity does not chain just the affinity 
                  1. IGM

                     Nota:

                     • -expressed in naeive B cells  -pentamer  -not a high affinity antibody  -linked by J chains  -very effiecient activating compliment 
                  2. IGG

                     Nota:

                     • Major class is serum  major class in secodnary response  binds receptor exposed by monocytes 
                  3. IGA

                     Nota:

                     •  Forms a monomer when its on the cell surface (bivalent) and dimer (tetravalent) when its secreted  Dimer is held together by a J chain that binds to the secretory component  The secretory IgA is prominent in mucosal secretions – airways, gut, breast milk  Best for vaccines
                  4. IGD
                     1. IGD

                        Nota:

                        • gD  On naïve b-cells  Found in low amounts in serum  Monomer  Similar to IgG but cannot cross placenta and does not activate complement  No effecter complement – cleaved off cell surface. Just recepto
                  5. IGE

                     Nota:

                     • Found in trace amounts in serum  Monomer  Important in responses to parasites  Can cause allergic reactions  
         2. Memory Cells