Chapter 7: Humoral Immunity

Question 1

Difference between IgM on surface of B cell and secreted IgM?

Answer 1

IgM on surface of B cell is a monomer; secreted IgM is a pentamer (highest avidity)

Question 2

How is the pentamer version of IgM held togeter?

Answer 2

By J chain synthesized by the cell

Question 3

Because IgM is incapable of binding to Fc receptors, what are some major disadvantages?

Answer 3

1. cannot act as an opsonin or;
2. cannot act as a mediator of anti-body dependent cell-mediated cytotoxicity (ADCC)

Question 4

Hyper IgM syndrome inheritance pattern?

Answer 4

X linked most commonly; can be acquired

Question 5

Describe the Ig levels in those with Hyper IgM syndrome?

Answer 5

IgG, IgA, and IgE are low
IgM elevated

Question 6

In addition to high numbers of IgM secreting plasma cells in those with X-linked hyper-IgM syndrome; what are there autoantibodies to found in the blood?

Answer 6

neutrophils, platelets, and red blood cells

Question 7

What are some symptoms of X-linked hyper IgM syndrome?

Answer 7

• patients fail to make germinal centers during a humoral immune response
• children with this condition suffer recurrent respiratory infections, especially those caused by Pneumocystis jirovecii

Question 8

What is the defect in hyper-IgM syndrome?

Answer 8

gene encoding the CD 40L, which maps to the X chromosome.

this causes failure of co-stimulatory signal needed for B cell response to T dependent ag. So only IgM is made

Question 9

What are the 4 sub-isotypes of IgG?

Answer 9

IgG1, IgG2, IgG3, and IgG4

Question 10

What are the major characteristics of IgG?

Answer 10

• activates complement
• acts as an opsonin, enhancing phagocytosis
• neutralizes pathogen and toxins
• mediates ADCC
• can cross the placenta via receptor mediated transport

Question 11

Where is IgA commonly produced?

Answer 11

in the submucosa more than in lymph or spleen

Question 12

Is IgA secreted as a monomer or dimer?

Answer 12

dimer

Question 13

What are the major functions of igA?

Answer 13

1. major protective defensed of the mucosal surfaces of the body
2. Any pathogen that infects the mucosa will induce IgA production by secretion of TGF-B by infected cells and to lesser extent IL-5
3. Functions as a neutralizing ab by inhibiting the binding of toxins or pathogens to the mucosa of the digestive, respiratory, and urogenital systems (sole function)

Question 14

What are the 2 isotypes IgA forms?

Answer 14

IgA1 and IgA2

Question 15

Can IgA activate complement?

Answer 15

no

Question 16

Can IgA mediated ADCC?

Answer 16

no

Question 17

Can IgA act as an opsonin?

Answer 17

no

Question 18

What does MALT stand for?

Question 19

What is MALT?

Answer 19

areas of the body where there is homing of specific memory cells to epithelial and mucosal surfaces leading to production of specialized lymphoid aggregations along these barriers

Question 20

What are some examples of MALT?

Answer 20

tonsils and Peyer’s patches;

numerous less well organized lymphoid accumulationns in lamina propria

Question 21

Describe the secretory portion of the IgA.

Answer 21

Its part of the receptor with which secretory IgA binds to in the epithelia; then it is endocytosed and released to lumen bound to secretory component

Secretory component provides important transepilthelial transport; but also protects from proteloytic cleavage

Question 22

Can IgE activate complement?

Answer 22

no

Question 23

Does IgE act as an opsonin?

Answer 23

no

Question 24

IgE binds directly to Fcε receptors on what types of cells?

Answer 24

mast cells, eosinophils, basophils

Question 25

Be able to reproduce the biologic functions of ab isotypes? (Which ones can activate complement classical pathway, neutralization, opsonization, ADCC, placental transport, Naive B-cell ag receptor, memory B cell antigen receptor (one only), trigger mast cell granule release)

Answer 25

Reproduce chart

Question 26

Which of the following is unique to IgG?
A. Placental transport
B. Neutralization and complement activation
C. Triggering mast cell granule release
D. Neutralization and ADCC
E. Opsonization and crossing the placenta

Answer 26

E. Opsonization and crossing the placenta