humoral immunity farmasi
TRANSCRIPT
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MICROBIOLOGY LAB
HUMORAL IMMUNE RESPONSE
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Humoral immunity to combate microbe
Be divided into innateandadaptive immunity
Innate immunity is performed by complement,which have main role to lyse extracellularmicrobes
Adaptive humoral immunity is conducted byantibodies (Ab), which have physiologic functionin defense against extracellular microbes andmicrobial toxin
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ANTIBODIES
(Immunoglobulins/Ig)
are circulating protein that are produced in
vertebrate in responses to exposure toforeign structures known as antigens
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Antigens Most are proteins or large polysaccharides from a foreign
organism.
Microbes: Capsules, cell walls, toxins, viral capsids,
flagella, etc.
Nonmicrobes: Pollen, egg white , red blood cell
surface molecules, serum proteins, and surface
molecules from transplanted tissue.
Lipids and nucleic acids are only antigenic when
combined with proteins or polysaccharides.
Molecular weight of 10,000 or higher.
Hapten: Small foreign molecule that is not antigenic.Must be coupled to a carrier molecule to be antigenic.Once antibodies are formed they will recognize hapten.
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AntigensEpitope:
Small part of an antigen that interacts with anantibody.
Any given antigen may have several epitopes.
Each epitope is recognized by a different
antibody.
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Epitopes: Antigen Regions thatInteract with Antibodies
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Antibody
produced by B ly in the lymphoid organ and bonemarrow
their effector function at sites distant from theirproduction
derived from long-lived plasma cells (in secondaryimmune responses by the activation of memory Bcells)
the effector functions are mediated by the heavychain (Fc) constant regions of Ig molecules, e.g.
phagocytosis Ab activates effector function when they are neededeffector functions are triggered by binding of Ag tothe variable regions (Fab)
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Antibody structure
The simplest molecular structure is calledmonomer has four protein chains : Two identical light chains (L-chain)
Two identical heavy chains (H-chain)
The chains are joined by disulfide (S-S)bonds/links to form a Y shaped or T shaped
The two arms of Y shaped is called variable (V)regions as antigen (epitope) binding sites (Fabregions)
The stem of Y shaped is called Fc regions
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Fab
Fc Hingeregion
Light
chain
Heavy chain
Ag binding
siteEpitope
ANTIBODY
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Antibodies can exist in two forms:
1. As membrane-bound antibodies on the surface
of B lymphocytes function as receptors for Ag
2. As secreted antibodies in the circulation, tissues,
and mucosal site which will bind antigens,
neutralized toxins, and prevent the entry and
spread of pathogens
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EFFECTOR FUNCTIONS of Ab
1. Neutralization of microbes and toxins
2. Opsonization and phagocytosis of microbes
3. Mediate ADCC (Ab dependent cell-mediated cytotoxic)
4. Lysis of microbes and inflammation through
the activation of complement
5. Feedback mechanism
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ANTIBODYFUNCTIONS
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Functions of Ab isotypes
Ab isotypes Effector function
IgG Opsonization of Ag for phagocytosis by Mo and neutrophils
Activation of the classical pathway of complement
ADCC mediated by NK cells and Mo
Neonatal immunity: transfer of maternal antibosy across the
placental and gut Feedback inhibition of B cell activation
IgM Activation of the classical pathway of complement Ag receptor of naive B cells
IgA Mucosal immunity:secretion of IgA into the lumens of GIT and resp tract
IgE o ADCC involving eosinophilso Mast cells degranulation (immediate hypersensitivity)
IgD Antigen receptor of naive B cells
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Neutralization of microbes and
microbial toxin
requires only the Fab region
most neutralizing Ab in the blood are ofIgG,
in mucosal organs are of the IgA isotype
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Neutralization
of microbes and
toxins
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Opsonization and phagocytosis
IgG isotype coat (opsonize) microbes and
promote their phagocytosis by binding to Fc
receptors on phagocytes
Mononuclear and neutrophils express receptor forthe Fc portion of IgG (FcRI)
Microbes may also be opsonized by a product of
complement activation (C3b)
The IgG and C3b are called opsonin
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Opsonization and phagocytosis
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Antibody-Dependent Cellmediated Cytotoxic (ADCC)
NK cells and other leucocytes bind to Ab coatedcells by Fc receptors and destroy these cells
Eosinophils mediate ADCC against helminth
coated by IgE through FcRI Engagement FcRIII (Fc receptor on NK cells)
activates the NK cells to synthesize and
secrete cytokine such as IFN- as well as the
content of the granule
(killing functions of NK cells)
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Antibody-Dependent Cell mediatedCytotoxic (ADCC)
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Complement functions
opsonization to enhance phagocytosis
phagocyte attraction and activation
through inflammation process lysis of bacteria
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Complementfunctions
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Consequences of AntibodyBinding
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Immunological Memory
Antibody Titer: The amount of antibody in theserum.
Pattern of Antibody Levels During Infection
Primary Response:
After initialexposure to antigen, no antibodiesare found in serum for several days.
A gradual increase in titer, first of IgM and thenof IgG is observed.
Most B cells become plasma cells, but some Bcells become long living memory cells.
Gradual decline of antibodies follows.
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Immunological Memory (Continued)
Secondary Response: Subsequent exposure to the same antigen
displays a faster and more intense antibodyresponse.
Increased antibody response is due to theexistence of memory cells, which rapidlyproduce plasma cells upon antigen stimulation.
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Antibody Response After Exposure toAntigen
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