Adaptive Immunity & B-Cell Formations

Question 1

What is an antigen in the context of adaptive immunity?

Answer 1

Small parts of a pathogen (like bacterial proteins) that trigger a specific immune response.

Question 2

What are the features of adaptive Immunity?

Answer 2

Specific – activated by and responds to a specific antigen

Versatility – ready to confront any antigen at anytime

Memory - ‘‘remembers’’ any antigen it has encounters

Tolerance – responds to foreign substances but ignores normal tissues

Question 3

Specificity

Answer 3

Receptors (BCRs and TCRs) recognize the unique shape of a specific antigen (often a small protein part of a bacterium).

Question 4

Versatility

Answer 4

Through random DNA rearrangement, your body produces millions of different receptors, ready for any possible invader.

Question 5

Memory

Answer 5

Upon first exposure, the body creates long-lived memory cells that make the second response nearly instantaneous.

Question 6

Tolerance

Answer 6

The “education” process ensures B and T cells that recognize “self” are deleted, preventing autoimmune attacks.

Question 7

How is “Versatility” achieved in B and T cells?

Answer 7

It is achieved through the random rearrangement of DNA that codes for their receptors, allowing for millions of different shapes.

Question 8

Define “Tolerance” and how it is achieved.

Answer 8

The ability to ignore “self” tissues. Achieved by negative selection: deleting B cells (in bone marrow) or T cells (in thymus) that react to self-proteins.

Question 9

Contrast BCRs and TCRs regarding antigen binding.

Answer 9

BCRs bind to extracellular antigens (in fluid). TCRs only bind to antigens displayed on MHC proteins on a cell surface.

Question 10

Describe the difference between Primary and Secondary Immune Responses.

Answer 10

Primary: Slower (takes ~2 weeks to peak), first encounter. Secondary: Faster and stronger due to memory cells; the basis for vaccinations

Question 11

Clonal Selection & Expansion

Answer 11

When a B or T cell in a secondary lymphoid organ (like the spleen) finally encounters its matching antigen, it undergoes Clonal Selection.

The Process: The “chosen” cell begins to divide rapidly (Clonal Expansion).

The Result: It produces two types of daughter cells:

Effector Cells: Short-lived cells that fight the current infection (e.g., Plasma cells).

Memory Cells: Long-lived cells that wait for the next encounter.

Question 12

Effector Cells

Answer 12

Short-lived cells that fight the current infection (e.g., Plasma cells).

Question 13

Memory Cells

Answer 13

Long-lived cells that wait for the next encounter.

Question 14

What is B-Cell Activation (The Humoral Response)?

Answer 14

“Humoral” immunity refers to defenses found in the blood and lymph. The B-cell is the star of this show.

Question 15

B-Cell Activation Process

Answer 15

Sensitization: Antigen binds to the B-Cell Receptor (BCR).

Internalization: The B-cell pulls the antigen inside, digests it, and displays fragments on MHC Class II molecules.

The “Handshake”: A Helper T-Cell recognizes the MHC-antigen complex and secretes cytokines.

Transformation: These cytokines trigger the B-cell to differentiate into Plasma Cells (which secrete antibodies) and Memory B Cells.

Question 16

What is the specific role of the Helper T-cell in B-cell activation?

Answer 16

It recognizes the antigen displayed on the B-cell’s MHC II and secretes cytokines that trigger the B-cell to proliferate and differentiate.

Question 17

What part of the antibody allows for “Clumping” (Agglutination)?

Answer 17

Antibodies have two antigen-binding sites (the Fab regions), allowing them to bridge and link multiple pathogens together.

Question 18

Fab Region (Arms)

Answer 18

Extremely variable; these bind to the specific antigen.

Question 19

Fc Region (Tail)

Answer 19

Constant; this determines the antibody’s class and interacts with immune cells

Question 20

How do antibodies work?

Answer 20

Neutralization: They “block” toxins or viruses from entering cells.

Agglutination: They clump pathogens together (since they have two binding sites).

Opsonization: They coat pathogens, making them easier for phagocytes to “eat” via Fc receptors.

Complement Activation: They trigger the classical pathway (forming the MAC).

Question 21

What is Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)?

Answer 21

When antibodies bind to a pathogen, NK cells or eosinophils use their Fc receptors to bind to the antibody tail and release chemicals to kill the pathogen.

Question 22

Which antibody is the most common in circulation and crosses the placenta?

Answer 22

IgG

Question 23

Which antibody is the first to be secreted during a new infection?

Answer 23

IgM (Excellent at clumping and activating complement).

Question 24

Which antibody is found in breast milk and protects epithelial surfaces?

Answer 24

IgA

Question 25

Which antibody is associated with allergic reactions and parasite defense?

Answer 25

IgE (Works with eosinophils and mast cells).

Question 26

Distinguish between Active and Passive Immunity.

Answer 26

Active: Your body makes its own antibodies/memory cells (infection or vaccine). Passive: You receive antibodies from another source (breast milk or clinical infusion); it is short-lived (~3 months).

Question 27

In a response to extracellular bacteria, what roles do innate and adaptive systems share?

Answer 27

The Innate system provides immediate inflammation and complement activation, while the Adaptive system provides specific antibodies that act as opsonins to enhance phagocytosis.