Dr Vinod KV Also known as antibodies They are glycoproteins produced by the body against antigenic stimulus Synthesised by B lymphocytes Basic structure Igs are glycoproteins Made up of two pairs of polypeptide chains ID: 934500
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Slide1
IMMUNOGLOBULINS
Structure, function and types
Dr.
Vinod
K.V.
Slide2Also known as antibodiesThey are
glycoproteins produced by the body against antigenic stimulus
Synthesised by B lymphocytes
Slide3Slide4Basic structure
Igs are
glycoproteins
Made up of two pairs of polypeptide chains
One pair light chains- L chains (mw 25000
da
)
One pair heavy chains-H chains (50000
da
)
L & H chain and H & H chains are joined by disulphide bond
4 chains are joined to form a flexible Y shaped molecule
Slide5Slide6Two regions-
Fab region &
Fc
region
Fab
region- at the tip of each arm of Y
Fc
region- limited in variability, responsible for the biological activity, act as receptor binding portion (to
phagocytic
cells), bind to complement
Ag binding site @ amino terminus
Ag binding site composed of both H & L chains
Slide7Both chains composed of two portions- variable region (N) & constant regions (C)
Constant region – constant sequence- One constant domain in L chain (C
L
) & 3-4 domains in H chain (C
H1
, C
H2
, C
H3
)
Variable region – one domain in both H & L chains- highly variable & determines immunological specificity
Hyper variable regions (hot spots)- highly variable region in the variable regions
Slide8Slide9Intra chain S-S bonds form loops form globular domains
VL & VH are responsible for Ag binding site
Hinge region- between CH1 & CH2 , flexible and more exposed to enzymes & chemicals
Slide10Slide11Slide12L chains are of two types- Kappa & lambda (2:1 ratio in human sera)
H chain 5 types- A, D, G, E & M
Slide13ANTIBODY STRUCTURE
Antigen
Variable region
Constant region
IMMUNITY
IMMUNITY
IMMUNITY
Different variable regions bind different antigens. Identical constant regions induce identical responses.
Slide14Classes of immunoglobulins
IgG
heavy chain is gamma
most common & major serum
Ig
(75-80%)
Circulating
Ig
equally distributed in intra & extra vascular compartments
Contains less CHO than other
Igs
mw 1,50, 000
da
, half life 23 days
8-16 mg/100 ml serum concentration
Exist as monomer
Only
Ab
that can cross placenta & provide natural passive immunitySecondary response Ab- second exposure- production of Ig G is very rapid
Slide15provide long term resistance
4 sub classes- Ig G1-IgG4
Functions
General purpose
Ab
, protective against agents in blood & tissues
Enhance
phagocytosis
Participate in most immunological reactions
neutralise toxins in blood & tissues
Best for opsonisation
Cross placenta
Slide16Ig
A
Second most abundant (10-13%)
mw 4,00,000
da
half life 6-8 days
Major
Ig
in
colostrum
, tear & saliva
Low in serum (0.6-4.2 mg/100ml)
Two forms- monomer (in serum) &
dimer
(in secretions called
secretory
Ig
A)Synthesised by plasma cells near mucosaHas a secretory piece produced by mucosa helps to cross mucos membrane & prevent from denaturation
J chain connect monomersSub classes- Ig A1 & Ig A2
Slide17Functions
Secretory Ig
A provide protection to respiratory & gastrointestinal tracts by inhibiting the attachment of the microbes to mucosa
Causes
degranulation
of
eosinophils
&
basophils
Enhance
phagocytosis
by
monocytes
Activate alternate pathway
weak in opsonisation
Slide18Ig
M
Third common
Ig
(5-8%)
occurs as a
pentamer
(J chain)- largest
Ig
First
Ig
to appear in circulation- Primary response
First
Ab
to be formed in
fetus
Deficiency is associated with
septicemia
Ig M is short lived, hence its presence indicate recent infectionFour constant domains500-1000 times more effective than Ig G in opsonisation, 100 times in bacterial action, 20 times in bacterial agglutination
Neutralisation is less effective
Slide19Function
Detection is useful in the diagnosis of syphilis, HIV, Dengue fever..Good at complement fixationCauses
lysis
of microbes
Effective in attaching to surface antigenic determinants
Responsible for protection against blood invasion by microbes
Slide20Ig D
Resembles
Ig
G in structure
Monomer
Mostly intravascular (3mg/100ml)
Half life 3 days
Occurs on the surface of
unstimulated
B cells
Cell Bound
Ig
D are k type, serum
Ig
D are L type
Slide21Functions
Helps in Ag recognition by B cellsBinding of cell bound Ig
D with Ag leads to stimulation of B cells, activation or cloning to produce
Ab
Slide22Ig
E
Resembles
Ig
G structurally
Monomer
Found only in mammals
mw 1,90,000
da
half life 2 days
Extravascular
Ig
Normal serum level in traces but elevated in allergic conditions
Affinity to surface of mast cells-helps to produce histamines
Mainly produced in the lining of respiratory & intestinal tracts
Slide23Function
Provide protection by being hypersensitiveCauses inflammatory responseSpecial role in defence against
helminth
infection
responsible for allergic reactions