Humoral Immunity

Question 1

What is humoral immunity?

Answer 1

Immunity provided by antibodies that are present in bodily fluid

Question 2

Humoral immunity refers to immunity mediated by?

Answer 2

B cells

Question 3

What is meant by T dependent antigen?

Answer 3

The B cell response to most antigens requires assistance from helper T cells (Th)

Question 4

What is meant by T independent antigen?

Answer 4

T independent antigen elicits antibody production by B cells without T cell involvement

Question 5

If an individual has an immune response to an antigen characterized by production of IgM but no IgG or IgA, what could you infer about the antigen?

Answer 5

The antigen is T independent

Question 6

What does class switching require?

Answer 6

CD40L on the surface of a T cell

Question 7

What can B cells act as professional antigen presenting cells for?

Answer 7

Antigen experience T cells

Question 8

Describe the structure of antibody

Answer 8

Consists of 2 identical heavy chains and 2 identical light chains. The two heavy chains are linked to each other by a disulfide bond. Each light chain has a disulfide bond linking it to one of the heavy chains. The entire structure weights about 150kDa.

Question 9

Describe the divisions of the antibody

Answer 9

2 parts: variable and constant
Variable: antigen binding
Constant: effector functions

Question 10

What else can the antibody be divided into?

Answer 10

Fab: Fragment antigen binding-there are 2 fabs
Fc: Fragment crystallisable-the constant region of the heavy chains

Question 11

What determines the isotypes/different classes of antibodies?

Answer 11

The heavy chain constant region

Question 12

Where is the “hinge” located?

Answer 12

Between the CH1 domain and the CH2 domain

Question 13

What are the hypervariable regions called, and why? (CDR1. CDR2, CDR3)

Answer 13

Complementarity Determining Regions

The amino acids within the CDRs are complementary to the amino acids in the antigen that is going to be recognized

Question 14

Which two classes of antibodies can polymerize or form polymers?

Answer 14

IgA and IgM

Question 15

Which antibodies are found in monomeric form?

Answer 15

IgA, IgD, IgE
Cell surface IgM
Circulating IgA

Question 16

Which antibodies are found in dimeric form?

Answer 16

Secretory IgA

Question 17

Which antibodies are found in pentameric form?

Answer 17

Circulating IgM

Question 18

What is the J chain?

Answer 18

A protein that joins together individual units of antibodies when they polymerize

Question 19

Which is the most dominant class of antibody in circulation?

Answer 19

IgG at 620-1400 mg/dL

Question 20

What are epitopes?

Answer 20

The area on the antigen that is recognized by the antibody. The larger the antigen, the more epitopes present.

Question 21

Why is the binding of an antibody to an antigen a reversible process?

Answer 21

All of the bonds involved are non covalent. Covalent bonds such as the disulfide bond between the chains of the antibody are irreversible.

Question 22

Amino acids in the Complementarity Determining Region interact with amino acids in the epitope using non covalent reversible forces. What are the four major forces involved?

Answer 22

1. Hydrogen binding
2. Electrostatic interactions
3. Van der Waals interactions
4. Hydrophobic interactions
   Overall binding strength=affinity

Question 23

What is functional affinity?

Answer 23

The

Question 24

What can antibodies, acting on their own do, when not acting as a bridge between the antigen and other components of the immune system ?

Answer 24

Neutralize bacterial toxins
Block viruses binding to cellular receptors
Block adherence of bacteria to mucosal surfaces

Question 25

Name ways in which antibodies act as a bridge.

Answer 25

• clearance of immune complexes by RBC (IgM, IgG )
• opsonization for phagocytes (IgG)
• antibody dependent cellular cytotoxicity (ADCD) (IgG)
• generation of membrane attack complex (IgM, IgG)
• mast cell degeneration (IgE)

Question 26

Give the functions of the IgM and IgG class

Answer 26

IgM: first class produced in adaptive response, activates complement, powerful agglutinin.BCR on B cells, secreted IgM mainly in circulation-pentamer with J chain. Can’t cross placenta

IgG: main antibody in 2nd response to antigen, most abundant in circulation, activates complement, opsonizes bacteria and beatralizes bacterial toxins and viruses. Only isotope that crosses placenta

Question 27

Give the functions of the IgA class

Answer 27

Secretory form prevents colonization at mucosal surfaces. Produced in GI tract and protects against gut infections.

Question 28

Give the functions of the IgD class

Answer 28

BCR (with IgM) on naive B cells. Found on surface of many B cells and in serum

Question 29

Give the functions of the IgE class

Answer 29

In presence of antigen, triggers release of inflammatory mediators from mast cells and basophils. Contributes to immunity to parasites by activating eosinophils. Lowest concentration in serum.