Microbiology – Basic Immunology Revised

Far  Eastern  University  –  Nicanor  Reyes  Medical  Foundation  

Microbiology  –    Basic  Immunology   Mary  Joyce  M.  Saborrido-­‐Teoxon,  M.D.     IMMUNOLOGY   − Study   of   body’s   protective   and   defensive   mechanisms   against   foreign  substances     − Discriminate  self  vs.  non  self   − Antigen-­‐antibody  reaction   − Eliminate  non-­‐self  (infectious  agents)       Immune  System   − Collection   of   organs,   tissues,   cells   and   soluble   factors   that   allow   individuals   to   defend   against   harmful   agents   such   as   viruses,   bacteria,  fungi,  parasitic  organisms,  and  tumor  cells     Two  (2)  Important  Roles  of  the  Immune  System:   1. Provides  defense  mechanism.   2. Identification  and  destruction  of  abnormal  cells.     HISTORY   Louis  Pasteur  –  father  of  immunology;  actually  the  one  who  discovered   the  rabies  vaccine   Edward  Jenner  –  discovered  “small  pox”  vaccine  from  cowpox     Innate  vs.  Adaptive  

 

First  Line  of  Defense   a.  Physiologic  Barriers   − Skin   • Hookworms  can  penetrate  skin   • Tinea  corporis   • Dermatophytes   b.  Chemica  Barriers   − Lysozymes:   chemical   barrier/enzyme   that   dissolves   some   bacterial   cell  wall   − Gastric  pH  of  the  stomach   c.  Biologic  Barrier   − Nomal  flora  (Lactobacillus  acidophilus)     Second  Line  of  Defense   − Phagocytes:  effective  only  for  extracellular  pathogens   − Anti-­‐microbial  proteins  and  inflammatory  response     ThirdLine  of  Defense   − Lymphocytes:    can  kill  intracellular  pathogens;  memory  cells     Acquired  Immunity:  Active  vs.  Passive   Active   –   actively   producing   antibody   after   an   exposure   to   an   antigen;   life-­‐long  protection   Passive   –   antibody   from   other   source;   immediate   but   short   term   protection   Natural  –  naturally  made;  can’t  be  produce  by  humans   Artificial  –  immunoglobulins;  commercially  availabe   Passive  Immunity   Natural   Artificial   → Placental  transfer  of  IgG   → Antibodies   or   immunoglobulins   → Colostral  transfer  of  IgA       → Immune  cells         Active  Immunity   Natural   Artificial   → exposure   to   sub-­‐clinical   → Vaccination   infections       Professional  Phagocytic  cells   − These  cells  have  enzymatic  constituents  in  their  granules  to  oxidize,   kill,  digest,  and  destroy  particulate  material  that  they  ingest.   nd − Part  of  2  line  of  defense       1. Mononuclear  phagocytes  (formerly  RES)   A.  Monocytes  (in  the  blood)   B.  Tissue  Macrophages   a.  Liver  àKupffer  cells   b.  Lungs  àAlveolar  macrophages/  Dust  cells   c.  Kidney  àMesangial  macrophages   d.  CNS  àMicroglial  cells   e.  Lymph  nodes  àDendritic  cells   f.  Skin  àLangerhan’s  cells  

 

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g.  Spleen  àSpleenic  macrophages    

h.  Connective  tissue  àHistiocytes   i.  Bone  àOsteoclast   j.  Peyer’s  pathches   k.  Tonsils  

    Functions  of  MØ   a. Phagocytosis   − Ingestion  &  killing  of  microbes   − Mostly  for  extracellular  pathogens   −  STEPS:   •  Chemotaxis  (C5a,LTB4,IL-­‐8,N-­‐formyl  methionine)   •  Diapedesis   •  Adherence   •  Engulfment/  Opsonins  (C3b,  IgG)   •  Phagosome  formation   •  Fusion   •  Digestion/Destruction       b. Antigen  Presentation   − Presentation   of   antigen   in   association   with   class   II   MHC   proteins  to  CD4  =  helper  T  cells   −  APCs:   •  MØ   •  B  cells   •  Langerhans  cells   •  Dendritic  cells       c. Cytokine  Production   − Synthesis   and   release   of   cytokines   such   as   IL-­‐1   &   TNF,   and   chemokines  such  as  IL-­‐8       2. Polymorphonuclear  leukocytes  (PMNs)   a. Neutrophils  (most  aggressive  phagocyte)   b. Eosinophils  (antiparasitic  phagocyte)   c. Basophils  (secretory  cells)       NK  cells   − LGL  /  Null  cells   − Lack  T  cell  receptor,  CD3  proteins,  and  surface  IgM  &  IgD   − Thymus  are  not  required  for  development  

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−  Activity  not  enhance  by  prior  exposure   −  Associated  w/  ADCC   −  CD56  &  CD16       Functions  of  NK  cells   − Kill  virus-­‐infected/  Cancer  cells   − Killing     • Non-­‐specific   • Not   dependent   on   foreign   antigen   presentation   by   class   I   or   II   MHC  proteins   • Activated  by  the  failure  of  a  cell  to  present  self  antigen   • Produce   perforins   &   granzymes,   w/c   cause   apoptosis   of   target   cell        Adaptive  Immunity   − Antigen  –  Antibody  reaction   − Cells:   •  B  cells   •  T  cells       Antigens  &  Immunogens   Antigens   → molecules  that  react  w/  Abs   → compound  that  does  not  necessarily  elicit  an  immune  response     Immunogens   → molecules  that  induce  an  immune  response  (antibody)   → at  least  2  antigenic  determinant   *All  immunogens  are  antigens,  but  not  all  antigens  are  immunogens.     Two  properties  of  Antigens:   − Immunogenecity:   ability   to   induce   specific   immune   response   resulting  to  formation  of  antibodies  or  immune  lymphocytes   − Antigenecity/   Specificity:     the   ability   to   react   specifically   with   the   antibody  or  cell  that  caused  it  to  be  produced     Parts  of  AG:   − Carrier  portion   • The  bigger  part  that  is  responsible  for  the  MW  of  antigen   • >10000  dalton  more  immunogenic   −  Epitome/  Antigenic  determinant   • Determines   specificity   of   antigen,   therefore,   an   antigen   w/out   epitope  is  said  to  be  nonspecific.   • Reactive  sites  (Ab/  TCR)     HAPTENS   − Molecule  that  is  not  immunogenic  by  itself  but  can  react  w/  specific   antibody   • Incomplete  Ag   •  Small  molecules  (