WEEK 2: B CELL MEDIATED IMMUNITY

Question 1

What is adaptive immunity?

Answer 1

A selective attack aimed at limiting or destroying a particular offending target for which the body has seen specially prepared after exposure to it.

Question 2

Describe the 2 classes of adaptive immunity.

Answer 2

*Antibody/ Humoral immunity: involves production of anti-bodies by B-lymphocytes derivatives called PLASMA CELLS.

*Cell mediated immunity: Production of activated T-lymphocytes which directly attach the unwanted cells.

Question 3

Describe the B-cells.

Answer 3

B-cells have B-cell receptors (BCR) on its surface for binding with particular type of the multitude of possible antigens.

Question 4

What are antigens?

Answer 4

A molecule that causes an immune response against itself when introduced into the body.

Question 5

State the 2 types of antigens that the B-cells respond to?

Answer 5

*T- independent antigens: They stimulate the production of antibodies by B-cells without any T-cell involvement. (Polysaccharide antigens)

*T-dependent antigens: Do not directly stimulate the production of antibody without the help of Special type of T-cells called Helper T-cells. (Protein antigens)

Question 6

Differentiate TD antigens and the TI type 1 and type 2 antigens under the following:

Isotype switching
Affinity Maturation
Immunologic memory
Polyclonal activation

Answer 6

TD antigens: Undergo all the following except Poly cyclonal activation. Hey are soluble proteins.

TI type 1 antigens: Only undergoes polyclonal activation.
Bacterial cell wall components, LPS

TI type 2 antigens: They have limited isotope switching and do not undergo the rest. Polymeric protein antigens, capsular polysaccharides.

Question 7

What types of antigens do most B-cells respond to?

Answer 7

T-dependent antigens

Question 8

What is a plasma cell?

Answer 8

An activated B-cell that can produce antibodies and become memory cells.

Question 9

Describe how B-cells differentiate to become plasma cells.

Answer 9

The B cell swells up as the rER greatly expands.

Because antibodies are produced, plasma cells essentially become prolific protein factories, producing up to 2000 antibodies molecules per second.

Question 10

Why is the lifespan of plasma cell 5-7 days(short)?

Answer 10

They concentrate on producing antibodies and cannot maintain protein synthesis for its viability and growth.

Question 11

What is the other term used to refer to antibodies?

Answer 11

Immunoglobulins

Question 12

State the 5 subclasses of anti-bodies.

Answer 12

*IgM
*IgG
*IgE
*IgA
*IgD

Question 13

Describe the IgM

Answer 13

*Serves as BCR for antigen attachment
*Is the first to be produced in the early stages of plasma cell response
* It is involved in ABO blood group antigens on the surface of RBC.

Question 14

Describe IgG

Answer 14

*It is the most abundant immunoglobulin in the blood
*Produced most specific immune responses against bacterial invaders.
*Has 4 subclasses.
IgG1
IgG2
IgG3
IgG4

*Opsonization, complement activation, Ab-dependent cell mediated cytotoxicity, neonatal immunity, passive immunity, feedback inhibition of B cells.

Question 15

Describe IgE .

Answer 15

*Helps protect against parasitic worms and is the antibody mediator for common allergic responses such as lay fever, asthma and hives.
*Found bound to basophils & mast cells

Question 16

Describe IgA

Answer 16

Found in mucosal surfaces, such as GIT, respiratory and urogenital systems.

Found In saliva, sweat, tears, colostrum, mucus.

Are responsible for neonatal passive immunity.

*Has 2 subclasses: IgA1, IgA2

Question 17

Describe IgD

Answer 17

Ag receptor on naive B cell.

Question 18

Describe the structure of an antibody.

Answer 18

*It has a Y shaped structure

*Immunoglobulins are constructed from two types of amino acid chains, heavy chains and light chains.

*Ig molecules contain two identical strands of heavy chains and two identical strands of light chains.

*The end with the two heavy chains forms a stable non-variable receptor point called an effector, which is the part of the Ig molecule that binds with our own immune system cells.

*On the opposite end of the antibody are two antigen binding sites, each with a light chain and heavy chain combination. This combination of light and heavy chains forms highly variable tips that can adapt to match a specific antigen.

Question 19

What are the functions of the following parts of an antibody?

*Arm region
*Tail region

Answer 19

ARM REGION: Determine specificity of antibody.

TAIL REGION: Determine function properties of the antibody.

Question 20

What is the Fab and Fc on an antibody?

Answer 20

Fab: Antigen binding fragment, are unique for each antibody.
They are found at the tip of the Heavy and light chains.

Fc: Constant region, identical within each antibody subclass.
-But they vary among the subclasses
-They are used to different the different immunoglobin subclasses.

Question 21

Describe the pathways taken by immature B and T lymphocytes to become activated immuno-competent B and T-cells.

Answer 21

*Lymphocytes destined to become T cells migrate to the thymus and develop immunocompetence there. B cells
develop immunocompetence in red bone marrow.

*After leaving the thymus or bone marrow as naive immunocompetent cells, lymphocytes “seed” the lymph
nodes, spleen, and other lymphoid tissues where the antigen challenge occurs.

*Mature (antigen-activated) immunocompetent lymphocytes circulate continuously in the
bloodstream and lymph and throughout the lymphoid organs of the body.

Question 22

Describe the chances that occur to the B cells in the lymph node.

Answer 22

Primary follicle: B cell activation

Secondary follicle: B cell proliferation and differentiation

Paracortex: Initial B cell and T cell activation.

Medulla: Plasma cell secretion.

Question 23

What are the 2 main processes in B-cell responses.

Answer 23

1.Recogniton phase
2.Activation phase: B cell proliferation

Question 24

What happens in recognition phase?

Answer 24

*Resting mature B cells are presented with an antigen.
*They become activated T cells
*Helper T cells and other stimuli act on them.

Question 25

Describe processes of B Cells Activation.

Answer 25

*Isotype switching

-Production of immunoglobulin from one type to various types.

*Affinity Maturation

-Activated B-cells produce antibodies with increased affinity (strength of binding) for antigen during the course of an immune response.
Result of somatic mutation of Ig genes.

*Memory B-cells

-Repeatedly generate an accelerated and robust antibody-mediated immune response in the case of re- infection/secondary immune response.

-Can survive for decades.

*Clonal Expansion

-Synthesis of multiple copies of B
cells that share affinity with and specificity of the same
antigen.

Question 26

Outline 3 Important B-cell Differentiation Events Take Place in Germinal Centers

Answer 26

1. Affinity Maturation:
2. Class Switch
3. Formation of plasma cells and memory cells

Question 27

What is clonal selection?

Answer 27

Clonal selection is the theory that specific antigen receptors exist on lymphocytes before they are presented with an antigen due to random mutations during initial maturation and proliferation.

PRIMARY RESPONSE
*After antigen presentation, selected lymphocytes undergo clonal expansion because they have the needed antigen receptor.

They form clones differentiate into active plasma cells and memory.

SECONDARY RESPONSE
(Can be after years when encountering the same antigen)

*The memory B cell will become plasma cell and produce antibodies and form other memory B cells.

Question 28

Differentiate between primary and secondary immune response.

Answer 28

PRIMARY
*Slow onset
*Low rate of antibody production
*Slow control of infection
*Innate immunity works alone, then joined by adaptive immunity.
*Lag phase 4-7 days
*Uses naive B and T cells

SECONDARY
*Rapid onset
*High rate of antibody production
*Rapid control of infection
*The adaptive and innate immunity work together from the start.
*Has 1-3 day lay phase
*Uses memory B and T cells

Question 29

Outline the 2 types of acquired immunity.

Answer 29

1.Active immunity: Production of antibodies as a result of exposure to ana antigen.

2.Passive immunity: The immediate immunity conferred on recipient of preformed antibodies.

Question 30

State the 2 subclasses of passive and active immunity including the examples.

Answer 30

ACTIVE IMMUNITY
*Natural: Infection
*ARTIFICIAL: Immunization

PASSIVE IMMUNITY
*Natural: -IgG from mother to fetus across placenta
-IgA form mother to baby via Breastfeeding and colostrum
*Artificial: Antibodies acquired from immune serum medicine.

Question 31

Describe the processes that generate antibody diversity.

Answer 31

*Antibody Gene Rearrangement: copy of each type of VDJ
gene segment to go in any given lymphocyte, generating an
enormous antibody repertoire.

*Junctional Diversity: arises when the fusion of V, D, and J
segments are not exact: can result from the deletion/addition of nucleotides.

*Antibody Isotype Switching: humoral immune response in
which a switch from IgM to another Ig follows first exposure to an antigen.

*Somatic Hypermutation: programmed process of mutation affecting the variable regions of immunoglobulin genes.

*Affinity Maturation: process by which B cells produce antibodies with increased affinity for antigen

Question 32

Describe the effector mechanisms of humoral immunity.

Answer 32

*Neutralization – Antibodies block binding of microbes and toxins to cellular receptors. e.g., Tetanus toxin

• Opsonization – Antibodies coat microbes and promote their phagocytosis. e.g. (Fc receptors, Macrophages)
• ADCC –Fc receptors of NK cells bind IgG Antibodies attached to cells – Antibody-coated cell lysis occurs.
• Complement fixation –cascade reacts to antigen antibody complexes.

*Agglutination and precipitation:
-Agglutination is the clumping of antigenic cells.

Question 33

Describe features of humoral immunity.

Answer 33

Specificity
*Ensures that distinct microbes elicit specific responses.

Diversity
*Enables immune system to respond to a large variety
of microbes.

Memory
*Leads to enhanced responses to repeated exposures
to the same microbe.

Specialization
*Generates responses that are optimal for defense
against different types of microbes.

Self-limitation
*Allows immune system to respond to newly encountered microbes.

Non-reactivity to self
*Prevents injury to the host during responses to
microbes