Immuno - Lymphocytes (B cells & Memory)

Question 1

Draw the structure of an antibody, labeling the following areas: (1) Fab (2) Fc (3) Antigen-binding site (3) V h (4) V L (5) D (6) J h (7) J L (8) C h1 (9) C h2 (10) C h3 (11) C L (12) Complement binding (13) Macrophage binding (14) Hinge (15) Sulfide bonds [S-S].

Answer 1

See p. 197 in First Aid for image in middle

Question 2

What part(s) of an antibody recognizes antigens?

Answer 2

Variable part of L and H chains recognizes antigens

Question 3

What part(s) of an antibody fixes complement? To what types of immunoglobulin does this apply?

Answer 3

Fc portion of IgM and IgG fixes complement

Question 4

To what part(s) of an antibody does the heavy chain versus light chain contribute?

Answer 4

Heavy chain contributes to Fc and Fab fractions. Light chain contributes only to the Fab fraction.

Question 5

What are the 2 major functions/purposes of the Fab fraction of an antibody?

Answer 5

(1) Antigen-binding fragment (2) Determines idiotype: unique antigen-binding pocket; only 1 antigenic specificity expressed per B cell

Question 6

How many antigenic specificities can each B cell express? What determines this?

Answer 6

only 1 antigenic specificity expressed per B cell; Fab determines idiotype: unique antigen-binding pocket

Question 7

What are the “C’s” to associate with the Fc fraction of an antibody?

Answer 7

(1) Constant (2) Carboxy terminal (3) Complement binding (4) Carbohydrate side chains

Question 8

What do the Fab versus Fc portions of an antibody determine?

Answer 8

Fab determines idiotype: unique antigen-binding pocket; Fc determines isotype (IgM, IgD, etc.)

Question 9

What are the 4 ways in which antibody diversity is generated?

Answer 9

(1) Random “recombination” of VJ (light-chain) or V(D)J (heavy-chain) genes
(2) Random combination of heavy chains with light chains
(3) Somatic hypermutation (following antigen stimulation)
(4) Addition of nucleotides to DNA during recombination (see 1st entry in this list) by terminal deoxynucleotidyl transferease

Question 10

Where on an antibody does complement bind?

Answer 10

Fc portion at Ch2 (IgG + IgM only)

Question 11

What result does antibody achieve in each of its following roles: (1) Opsonization (2) Neutralization (3) Complement activation?

Answer 11

(1) Antibody promotes phagocytosis (2) Antibody prevents bacterial adherence (3) Antibody activates complement, enhancing opsonization and lysis

Question 12

What type(s) of immunoglobulin do mature B lymphocytes express of their surfaces? How are other types of immunoglobulin generated?

Answer 12

Mature B lymphocytes express IgM and IgD on their surfaces; They may differentiate by isotype switching (gene rearrangement; mediated by cytokines and CD40 ligand) into plasma cells that secrete IgA, IgE, or IgG

Question 13

What is the main antibody isotype in secondary (delayed) response to an antigen? Which antibody isotype is produced in the primary (immediate) response to an antigen?

Answer 13

IgG; IgM

Question 14

What is the most abundant antibody isotype in serum?

Answer 14

IgG

Question 15

What 4 major functions do IgG antibodies serve?

Answer 15

(1) Fixes complement, (2) Crosses the placenta (provides infants with passive immunity), (3) Opsonizes bacteria, (4) Neutralizes bacterial toxins and viruses.

Question 16

What primary function does IgA serve? What is important to know about its production level? Where is it found?

Answer 16

Prevents attachment of bacteria and viruses to mucous membranes; Most produced antibody overall, but released in secretions (tears, saliva, mucus) and early breast milk (known as colostrum)

Question 17

Does IgA fix complement?

Answer 17

No, does not fix complement

Question 18

In what form is IgA in circulation versus when secreted?

Answer 18

Monomer (in circulation) or Dimer (when secreted)

Question 19

How does IgA cross epithelial cells? What is the significance of epithelial cells to IgA function?

Answer 19

Crosses epithelial cells by transcytosis; Picks up secretory component from epithelial cells before secretion

Question 20

Give one major thing IgG and IgM have in common and one major difference between them.

Answer 20

Both fixes complement; but IgM does not cross the placenta (unlike IgG)

Question 21

Which antibody isotype(s) is/are found on the surface of B cells?

Answer 21

IgM = antigen receptor on the surface of B cells; IgD = found on surface of many B cells

Question 22

What are the forms of IgM, and in what contexts? What is the significance of IgM’s form change?

Answer 22

Monomer on B cell or pentamer when secreted; Shape of pentamer allows it to efficiently trap free antigens out of tissue while humoral response evolves

Question 23

What is the function of IgD antibody? Where is it found?

Answer 23

Unclear function; Found on the surface of many B cells and in serum

Question 24

Which antibody isotype has the lowest concentration in serum ?

Answer 24

IgE

Question 25

What kinds of cells does IgE bind? What function(s) does IgE serve, and via what mechanisms?

Answer 25

Binds mast cells and basophils; Cross-links when exposed to antigen, mediating immediate (type I) hypersensitivity through release of inflammatory mediators such as histamine. Mediates immunity to worms by activating eosinophils.

Question 26

What characterizes thymus-independent antigens? What kind of immunogenicity do they have, and how does this effect vaccinations?

Answer 26

Antigens lacking a peptide component (e.g., lipopolysaccharides from gram-negative bacteria), cannot be presented by MHC to T cells; Weakly or nonimmunogenic, vaccines often require boosters (e.g., pneumococcal polysaccharide vaccine).

Question 27

What characterizes thymus-dependent antigens? What impact do they have on antibodies and immunologic memory?

Answer 27

Antigens containing a protein component (e.g., diphtheria vaccine); Class switching and immunologic memory occur as a result of direct contact of B cells with Th cells (CD40-CD40 ligand interaction)