Classes of immunoglobins

Question 1

how many classes/isotypes of immunoglobin and how are they classed

Answer 1

5 different classes- based on differences in the aa sequences in constant region of the heavy chain
serum of a normal individual will contain all 5 different isotypes. The heavy chain is the principle determinant of the class

Question 2

What are the % different isotypes

Answer 2

IgG-γ heavy chains
IgA- α heavy chains
IgM- μ heavy chains
IgD- δ heavy chains
IgE- ε heavy chains

Question 3

immunoglobulin types

Answer 3

Immunoglobins can also be classified by the type of light chains. Light chains can either be a kappa κ of lamda λ light chain

Heavy chains of each class (γ α μ δ ε ) will pair up with two identical light chains κ or λ .

Question 4

IgG

Answer 4

most abbundant in serum 
4 subtypes 
IgG major role in binding antigen
readily diffuses into extravascular space major role in neutralising bacterial toxins, binding to microorganisms ( increase phagocytosis ) and inactivating viruses ( prevent binding to host cell receptors)
can trigger complement fixation

Question 5

complement system

Answer 5

a collection of serum glycoproteins that initiate a cascade that can perforate cell membranes

Question 6

complement can

Answer 6

• perforate cell membranes
• opsonization - promotion of phagocytosis
• recruit/activate cells (neutrophils, macrophages)
• participate in regulation of antibody responses
• aid in the clearance of immune complexes and apoptotic cells

Question 7

mechanisms of complement fixation

Answer 7

• bind to Ig or to membrane components of cells
• proenzymes cleave other complement proteins
• cleavage products activate cells
• increase permeability or opsonize bacteria

Question 8

Phagocytosis

Answer 8

(Macrophage, neurophils, polymophonuclear cells)
Phagocytic cells have a variety of receptors on membrane surface 1.Fc receptors- Bacteria bound to IgG antibody have Fc region exposed. Binds to the receptor on phagocytes. 2.Complement receptors- C3b receptor. Binding of C3b-coated bacteria to receptor results in enhanced phagocytosis and stimulation of respiratory burst.
Phagocytosis- increase in glucose and oxygen consumption (respiratory burst)(oxygen dependant intracellular killing) or pre formed substances released from intracellular granules or lysosomes that fuse with the phagosome (oxygen independent intracellular killing)

Question 9

IgG- antibody dependant cell mediated cytotoxicity (ADCC)

Answer 9

Antibody bound to virus infected cell. Links Fc receptor of natural killer cell. Antibody acts as a siren alerting the NK cells which recognise and secrete cytokines to attack and kill the infected cell

Question 10

Fc receptors

Answer 10

Trigger effector functions

• variety of Fc receptors with different specificities for different Ig classes
• The receptor protudes from membrane of certain cells such as Natural killer cells and macrophage
• FcγR1 specifically binds Fc fragment of IgG
• Long half life (about 20 days)
• Different antibodies will bind to different Fc receptors and thus initiate various cellular immunological responces.

Question 11

other important roles for IgG

Answer 11

• IgG only immunoglobulin which can cross the placenta from mother to foetus(transcytosis). Thus essential in providing infant with immunity for first few weeks of life.
• also present in colostrum(liquid which precedes milk from mammary gland) Reinforces immunity of newborn when infant drinks>IgG crosses the intestinal wall of new born into blood stream( receptor mediated endocytosis)

Question 12

Transcytosis

Answer 12

IgG will bind to specific receptor that causes the IgG to be engulfed in a vesicle which passes through the cell and releases the antibody at the other side at the cell membrane

Question 13

Immunoglobin A

Answer 13

constitutes 10-15% Ig in serum
Predominant Ig in secretions (saliva, tears, sweat ect)
also present in colostrum
function- to protect the extrenal surfaces of body against microorganisms