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Immuno globulins=Ig

They are a group of (glycoproteins) which present In serum, tissue and all body fluids of all vertebrates , that have Antibody (Ab) activities (react Specifically with the Antigen (Ag) that causes their Productions These Abs play a major role in defense mech. and Protection against infections Ig are synthesized and secreted by plasma cell

Which are the end stage of activated & differentiated B lymphocyte
B
P
Ab
Ag
Ab


constitute about 20% of serum proteins & consist of 82-96% polypeptide (back bone) 4-18% CHO which support them against proteolytic enzymes Basic structure of Ig : The backbone of Ig consist of 2 pairs of polypeptide chains each pair are identical. One pair nearly double the molecular weight of the other pair so called heavy & light chain respectively

Basic str. Of Ig.

The 4 chains are hold together by inter chain disulphide bonds to give us this monomeric Structure .

Each chain has 2 terminals: 1-Amino ter. In which the a.a. are variable called (variable region) 2-Carboxy ter. In which the a.a. sequence rather consist & heterogeneous (constant region)


Hot spot (hyper variable region): 3 areas in the variable region of each chain with a high variability in the a.a. sequence to form the Ag binding site (paratope) Paratope=Ag binding site A cleft formed by 3 hot spots from the light chain & a farther 3 from the adjacent heavy chain ,it is complementary to the specific chemistry & shape of the epitope (Ag determinant) Idiotype =paratope +hot spots

paratope

Constant region
Constant region
Paratope Hote spote
Variable region
Variable R. light heavy
COO
Idiotype

Epitopes: Antigen Regions that Interact with Antibodies

constant region: Light chain either: Kappa  Lambda  Heavy chain either: IgG
IgA
IgM
IgD
IgE
(5 classes)
2:1
    


The a.a. sequence in both light & heavy chains is not a linear sequence but there are domes or loops due to presence of intra chain disulphide bonds these globular areas called domains

In the variable region of each chain there is only one domain VL or Vh In the constant region of light chain there is one constant domain CL In the constant region of heavy chain There are 3 constant domains CH1,CH2,CH3 with exception IgM, IgE there is an extra domain CH4

Complement fixation

Complement fixation


Pepsin act to the right of hinge region leads to formation of FAB Dimmer (FAB)2 & FC fragment
Pepsin


Function of Ig Ig is a bi-functional mol. primary binding with Ag Ag (recognition) secondary biological activities to get red of invasion Ag Cytolysis: Ag-Ab binding activation of the complement sys. Lysis of the cell


Opsonization Ab coat the Ag recognized by phagocytic cells phagocytosis (phagocytic cell like macrophage ,monocyte ,natural killer have receptor For FC fragment of Ig Neutrilization Neutralize toxins & viruses Blocking block the reaction Agglutination

Ig classes they are classified: On the bases of their heavy chain peptide str. IgG: -predominant Ig in serum75% -M.W. low 150000 -can extra-vassate easily to the extract vascular space so 1st line of defense -Only Ig can pass the placenta protect the fetus in the 1st few month of life -Long half time -Best opsonizing Ab ,it binds the Ag with high affinity

-Main Ig in the secondary immune response The chain of IgG is subdivided into: 4 subclasses


IgG
65%
IgG
32%
IgG
8%
IgG
4%
1
2
3
4
1
2
3
4


These subclasses differ in their secondary biological activity -complement fixation (CH2) through classical pathway IgG IgG IgG While IgG only fix complement through alternative path -crossing the plasenta (CH3 ,CH2) IgG IgG IgG -binding to monocyte (CH3 ,CH2) IgG IgG IgG -blocking IgE binding only IgG4
3
1
2
4
3
1
2
1
2
3
4


IgG is considered the most protective Ab: because 1-present in high amount in blood (75%) 2-Extra vassate easily to extra vascular space 3-can cross the placenta 4-Binds avidly with Ag (of high affinity) 5-Very efficient opsonizing Ab 6-Can activate the complement system through the classical path way

Opsonization: Substances that bind to particles & make them more susceptible to phagocytosis: 1-complement compound C3b 2-Antibodies IgG, IgA 3-Fibronectin glycoprotein glue. 4-Leukotrienes B4 5-C. reactive protein

summary

Ref. Jawedez microbiology Hide


Choose the most appropriate answer (only one) 1-The antigen binding side of immunoglobulin is called; a-epitope b-paratope c-isotype d-allotype e-C & d are true




رفعت المحاضرة من قبل: Abdalmalik Abdullateef
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