B cells

Question 1

Antigen (Antibody generator): compound that elicits an
adaptive immune response
– Can be bound by?

Answer 1

A specific BCR (antibody) or TCR

Question 2

Nature of BCR antigens is greatly varied

Answer 2

– Proteins and polysaccharides are typical antigens
– Lipids and nucleic acids are rarely antigens
– Size is important for antigenicity
>10 kDa more likely antigens

Question 3

What is an Immunogen?

Answer 3

A molecule that causes adaptive immune response if injected alone

Question 4

An Epitope is?

Answer 4

Antigenic determinant; part of antigen where antibody (or TCR binds)

Question 5

Basic unit of the antibody structure is the?

Answer 5

Y-shaped monomer
– 4 chains held by disulfide bonds
2 “heavy” chains
2 “light” chains

Question 6

Antibodies are?

Answer 6

proteins made up of 4 amino acid chains

Question 7

Each chain of an antibody has a constant region

Answer 7

– This region of the heavy chain contains the Fc region

– Heavy chain determines Fc region and isotype

Question 8

Each chain of an antibody has a variable region

Answer 8

– Variable region is unique
– 1 heavy chain variable region and 1 light chain variable region together forms the antigen binding site
2 Ag binding sites/antibody

Question 9

Blocks toxin or virus from interacting with cell

Answer 9

Neutralization

Question 10

Binds cellular structures to interfere with function

Answer 10

Immobilization & prevention of adherence

Question 11

Clumping of bacterial cells by specific antibody. Bacteria more easily phagocytized

Answer 11

Agglutination & precipitation

Question 12

Multiple antibodies bind a target cell making it a target for NK cells

Answer 12

Antibody-dependent cellular cytotoxicity

Question 13

Isotype determines functional relationships of antibody

– Interactions with cells

Answer 13

– Interactions with cells
Fc receptor binding
– Tissue distribution
– Monomeric, dimeric, or pentameric structure

Question 14

IgG and IgM are the primary?

Answer 14

plasma isotypes

Question 15

IgG and monomeric IgA are the?

Answer 15

major extracellular fluid isotypes

Question 16

Dimeric IgA is in?

Answer 16

secretions across epithelia, including breast milk

Question 17

IgG is the only?

Answer 17

transplacental isotype

Question 18

IgE is typically associated with?

Answer 18

mast cells (especially in the respiratory tract, GI tract, & skin)

Question 19

The brain is normally devoid of?

Answer 19

immunoglobulin

Question 20

During lymphocyte development, B and T cells

acquire ability to?

Answer 20

recognize distinct epitopes
– Once they make a TCR or BCR, cells “checked out”
to ensure proper function
– B cells undergo developmental stages in bone marrow
– T cells go through process in thymus

Question 21

Antigen receptor diversity: Recombination of DNA allows ?

Answer 21

generation of novel variable regions of antigen receptors

– Applies to BCR and TCR

Question 22

Antigen receptor diversity: Junctional diversity

Answer 22

nucleotide additions occur at the junction sites

– Applies to BCR and TCR

Question 23

Two chains form antigen binding site

Answer 23

– Applies to BCR and TCR:
BCR = light and heavy chain
TCR = α and β chains form TCR

Question 24

Somatic hypermutation for?

Answer 24

affinity maturation

– Applies to BCR/antibody only

Question 25

B Lymphocyte characteristics include?

Answer 25

– Naïve
* Have antigen receptor but have not encountered antigen
– Activated
* Able to proliferate
* Have bound antigen
– Effectors:
* Descendants of activated lymphocytes
* Able to produce specific cytokines
* Plasma cells
– Memory lymphocytes
* Long-lived descendants of activated lymphocytes
* Memory cells responsible for seed and effectiveness of secondary response
– Remembers antigen on subsequent exposure

Question 26

When antigen enters body, only specific antibody binds

– Initiates multiplication of antigen specific B cells. Process called clonal selection

Answer 26

Repeated cycles of cell division generates population of copied antibodies
– Termed clonal expansion
- Without sustained stimulation, cells undergo apoptosis

Question 27

Humoral Immunity

Answer 27

Mediated by B lymphocytes a.k.a B cells
– Develops in bone marrow
– B cells may be triggered to proliferate into plasma cells
Plasma cells produce antibodies
– Antibodies produce when antigen bonds B cell receptor
– Some B cells differentiate into memory cells

Question 28

B Lymphocyte Activation 7 steps

Answer 28

1. Ag binds to B cell receptor
   – Poises B cell to respond; still needs help from CD4 T cells
2. Ag is phagocytized and processed by B cells
3. B cell presents a peptide cut from the antigen on MHCII
4. TH cell with specific TCR recognizes the peptide: MHCII
   complex and co-stimulates the B cell
5. B cell is activated & proliferates
6. Optimizes BCR/antibody
7. Plasma & memory cells

Question 29

B Lymphocyte and Antibody Response:

Characteristic of primary response

Answer 29

Lag period of 10 to 12 days occurs before antibody
detection in blood
* Activated B cells proliferate and differentiate into increasing numbers of plasma cells as long as antigen is present
– Net result is slow steady increase in antibody titer

Question 30

Over time, some B cells undergo changes enhancing immune response including?

Answer 30

Affinity maturation

Isotype (Class) switching

Question 31

Affinity maturation by somatic hypermutation

Answer 31

– Demonstration of evolution: natural selection
* Occurs among activated proliferating B cells in 2° lymphoid tissue
– Point mutants in the variable region of the BCR are formed
* Many cells have unproductive mutations (nonsense) and the cell will die
* Many cells will have less effective BCRs and will die
* Rarely, a mutation will make the antibody bind better and that cell will be further stimulated and optimized
* Because this is a rare event LOTS of B cells need to be produced to generate the best antibody
– Fine tunes the quality of antibody binding to antigen

Question 32

Isotype (Class) switching

Answer 32

– B cells initially programmed to produce IgM
– Helper T cells produce cytokines upon co-stimulation
Can induce B cells to switch isotypes
– Differentiate to plasma cells that secrete other classes of
antibodies
Commonly IgG
Can be IgA or IgE too

Question 33

Formation of memory B cells

Answer 33

B cells that have undergone class switching
IgG is primary antibody of memory
IgG antibody can circulate in body for years allowing
protection against specific antigens

Question 34

Characteristics of secondary response for B cells

Answer 34

Memory cells responsible for swift effective reaction
of secondary response
* Often eliminate invaders before noticeable harm is done

Question 35

Vaccine exploits phenomenon of immunologic memory
– Some memory B cells will differentiate into plasma cells
Results in?

Answer 35

rapid production of antibodies

Question 36

T-independent antigens

Answer 36

– Can stimulate antibody response
* Activate B cells without helper T cells
* Few antigens are T-independent
– B cell receptors bind antigen simultaneously
* Clusters BCRs and leads to B cell activation
– Some polysaccharides and lipopolysaccharides act as T-independent antigens
– No T cells, so only IgM produced and no memory

Question 37

TH cells in B cell activation

Answer 37

If TH cell encounters B cell bearing peptide: MHCII complex
– TH cell responds by producing cytokines
– B cell is activated in response to cytokine stimulation
* B cell proliferates and undergoes class switching
Also drives formation of B memory cells

Question 38

Natural killer cells descend from lymphoid stem cells. They?

Answer 38

They lack antigen specificity
- No antigen receptors
- Recognize antigens by means of Fc portion of IgG antibodies
– Fc receptors allow NK cells to attach to antibody-coated cells

Question 39

NK Actions assist the adaptive immune response

Answer 39

Important in process of antibody dependent cellular toxicity

- Enable killing of host cells with foreign protein in membrane

Question 40

Natural killer cells recognize damaged host cells with no
MHC class I surface molecules, Important in?

Answer 40

viral infection