Unti 2 - Lecture 10 Adaptive Immunity

Question 1

What are some comparisons of the innate and adaptive immunity?

Answer 1

Question 2

What are some characteristics of Adaptive (specfic) Immunity?

Answer 2

• Includes B and T lymphocytes

—B lymphocytes are born and mature in the bone marrow.

—-T lymphocytes are born in the bone marrow and mature in the thymus gland.

• Lymphatic system supplies lymphocytes to the bloodstream.
• Lymphocytes congregate in the lymph nodes and exit through the outgoing lymph vessels.

—–Interaction with innate immune cells (dendritic cells)

Question 3

What is the Lymphatic System?

Answer 3

Lymphatic System

• Part of the circulatory system
• Network of conduits called lymphatic vessels
• Carries a clear fluid called lymph which contains white blood cells

Question 4

What is the Primary Lymphoid Organs?

Answer 4

• Sites of lymphocyte maturation
• Bone marrow and thymus

Question 5

What are Secondary Lymphoid Organs?

Answer 5

• Sites of lymphocyte activation
• Lymph nodes, tonsils, spleen and Perer’s patches

Question 6

What are lymph nodes?

Answer 6

• Organized lymphoid tissue distributed widely throughout the body
• 500-600 in humans
• Act as “filters” or “traps” for foreign particles
• Dendritic cells take up antigens and activate lymphocytes
• Become inflamed or enlarged during infection
• Outer cortex: B cells and T cells
• Inner medulla: macrophages, B cells, and plasma cells

Question 7

What is involved in the spleen?

Answer 7

• Located in the left abdominal cavity
• Specializes in filtering blood and trapping blood-borne antigens/pathogens
• Dendritic cells take up antigens and activate lymphocytes
• Become inflamed or enlarged during infection
• Red pulp: Destruction/removal of old or defective red blood cells.
• White pulp: populated by T and cells
• Germinal centers: site where mature B cells rapidly divide, differentiate, and undergo somatic hypermutation

Question 8

A cell of the adaptive immune system such as

B cell.

What is a B cell?

Answer 8

A “B” cell is an antigen binding receptor (antibody)

• Primary function is to make antibodies (also called immunoglobulin)
• Surface B cell receptor is identical to the antibody secreted
• Recognize antigens in their native form (soluble antigens)
• Activation and function “helped” by CD4+ T cells

Question 9

With antibody production what is the Humoral Response?

Answer 9

• Humoral= “arising from the body”
• Serum= unclotted portion of blood

—-Complement and antibodies
•Antibody half-life 7-23 days
•Also found in mucosal secretions (IgA)

Question 10

What are antibodies?

Answer 10

• Recognize a unique part of a foreign invading microbe called an antigen
• Y-shaped protein
• 2 identical heavy chains (VH)
• 2 identical light chains (VL)
• Linked via disulfide bridges
• Two antigen binding sites (Fab regions)
• Fc region mediates antibody function

Question 11

What is the Antibody Structure?

What is the affinity?

Answer 11

Affinity: Strength which an antibody binds to a antigen

Question 12

What are Antibody Isotypes?

Answer 12

• Five major classes of antibody:

1. IgM
2. IgG
3. IgA
4. IgD
5. IgE

• Differ in heavy chain Fc region structure
• Different structural and functional properties

Question 13

What is Immunnoblobulin (IgG)?

Answer 13

• Makes up ~80% of serum antibodies
• Monomer with 2 antigen-binding sites
• Fc portion:

Activates classical complement pathway
Enhances phagocytosis
Bind to NK cells to mediate cytotoxicity
Only class able to cross the placenta and enter fetal circulation

Question 14

What is Immunoglobulin M (IgM)?

Answer 14

• Makes up ~13% of serum antibodies
• Half-life of about 5 days
• Low affinity
• Pentamer with 10 antigen-binding sites

Joining (J) chain needed for pentameric form

• First class produced in primary response to an antigen/pathogen
• Monomeric form expressed on surface of B cells (BCR)
• Fc portion:

Most efficient class for activating the classical complement pathway

Question 15

What is Immunoglobulin A (IgA)?

Answer 15

• Found mainly in body secretions

Saliva, tears, milk

• Dimer with 4 antigen-binding sites
• Secretory component critical for transport into secretions and protection from digestive enzymes
• Protects mucosal surfaces by blocking viral attachment

Question 16

What is a humoral Response?

Answer 16

• Mature B cells patrol the lymphatic system
• Binding of antigen/microbe to BCR triggers activation, and cell division, differentiation
• Plasma cells

Antibody producers
Long-lived producers reside in bone marrow

• Memory cells

Long-lived cells
Generate secondary responses

Question 17

What are T-independent Antigens?

Answer 17

• Antigen able to fully activate B cells without T cell help
• Usually “repeated” structures

Polysaccharides
Envelope glycoproteins

Question 18

What are T-dependent Antigens?

Answer 18

• Antigens that do not directly stimulate antibody production
• Requires the T cell help
• Protein molecules

Question 19

Descibe T-Cell Mediated Immunity

Answer 19

• T cells recognize “cells” that contain foreign antigens (e.g., virally infected cells).
• B-cells and T-cells recognize fundamentally different viral structures.

B-cells recognize whole protein antigens.
T-cells recognize processed short viral peptides.

• At least two defined populations of T cells

Cytotoxic T cells (TC)
T helper cells (TH)

• Express a unique T cell receptor (almost unlimited specificities)
• Recognize antigens displayed on the surface of antigen-presenting cells
• Primary functions are cytokine secretion (CD4) and cytotoxicity (CD8)

Question 20

What is Antigen Presentation?

Answer 20

Microbial antigens broken down into short peptide sequences

External antigens

• MHC class II
• CD4 T cells

Internal antigens

• MHC class I
• CD8 T cells

Question 21

B cells work in Concert with TH2 cells

What are the cytokines involved?

Answer 21

Cytokines play a major role in activating or communicating between B and T cells

Question 22

Summary of the lecture

Answer 22

Adaptive immune system takes longer to develop, is highly specific, and results in the generation of immunological memory
T cells are generated in the thymus and B cells are generated in the bone marrow
Lymphocyte activation occurs in secondary lymphoid organs such as the spleen and lymph nodes
B cells secrete different isotypes of specific antibody, each with a different functionality
T cells come in two types, CD4+ and CD8+
CD4+: “helper” cells; activated by external antigens via MHC class II
CD8+: “killer” cells; activated by internal antigens via MHC class I
Innate and adaptive immune systems are “linked” to coordinate effective clearance of pathogens and resolution of disease