Lecture 4 - Adaptive Immunity

Question 1

Hematopoietic Stem Cell differentiation

Answer 1

Stem cell in bone marrow that differentiates to:
— Myeloid Progenitor Cells (which mostly differentiate to innate immunity cells)
— Lymphoid Progenitor Cells (which mostly differentiate to adaptive immunity cells)

Question 2

Myeloid Progenitor Cell differentiation

Answer 2

— RBCs
— Platelets
— Neutrophils - innate immunity
— Eosinophils - innate immunity
— Basophils - innate immunity
— Monocytes - innate immunity

Question 3

Monocyte differentiation

Answer 3

— Dendritic cells
— Macrophages

Question 4

Lymphoid Progenitor Cell differentiation

Answer 4

— T Lymphocyte - adaptive immunity
— B Lymphocyte - adaptive immunity
— Natural Killer Cells - innate immunity

Question 5

T Lymphocyte differentiation

Answer 5

— Helper cells
— Regulatory cells
— Cytotoxic cells

Question 6

B Lymphocyte differentiation

Answer 6

— Plasma cell to detect antibodies

Question 7

Adaptive immunity

Answer 7

Immune response mediated by B and T lymphocytes (B cell/ T cell) to infectious agents and noninfectious molecules

Responses are generated in response to antigens

Question 8

Innate vs Adaptive immunity

Answer 8

Innate:
- Detects common microbial
structures
- Receptors are encoded in the
germline
- Same response upon repeat
exposure

Adaptive:
- Detects vast repertoire of
molecules
- Receptors generated by somatic
recombination
- Improved “adapted” response to
repeat exposure

Question 9

Antigen (Ag)

Answer 9

A molecule, typically from a pathogen, that is recognized by an antibody

Question 10

Types of Antigens recognized by B cells

Answer 10

1. Proteins
2. Lipopolysaccharides
3. Lipids
4. Nucleic acids

Question 11

Types of Antigens recognized by T cells

Answer 11

Peptides derived from Proteins

Question 12

T Lymphocytes (T Cells)

Answer 12

Adaptive immunity cells that require antigen presentation by dedicated antigen presenting cells (APC)

T cells require co-receptors to assist antigen recognition

Question 13

Antigen Presenting Cells (APC)

Answer 13

Cells that present antigens that can be recognized by T cells

Reside in potential sites of Microbe entry (skin, G.I. tract, respiratory tract, etc.). APCs capture, process and present antigens to T lymphocytes in peripheral lymphoid tissues

Question 14

TCR

Answer 14

T Cell Receptor

A single TCR recognizes a single presented antigen

Question 15

B Lymphocytes (B Cells)

Answer 15

Adaptive immunity cells with BCRs that directly recognize its cognate antigen

There are millions of B cells each with a unique BCR

Question 16

Two forms of Adaptive Immunity

Answer 16

1. Humoral Immunity
2. Cellular Immunity

Question 17

Humoral Immunity

Answer 17

Type of adaptive immunity

Directed against extracellular microbes and mediated by B lymphocytes.

B lymphocytes secrete antibodies that neutralize and eliminate microbes and microbial toxins

— Microbe: extracellular microbes
— Responding lymphocytes: B lymphocyte
— Functions: block infections and eliminate extracellular microbes

Question 18

Cellular Immunity

Answer 18

Type of adaptive immunity

Directed against intracellular microbes and mediated by T lymphocytes.

T lymphocytes activate phagocytes and lymphocytes or kill infected host cells

— Microbe: phagocytosed or intracellular microbes
— Responding lymphocytes: helper or cytolytic T lymphocytes
— Functions: activate macrophages to kill phagocytosed microbes or kill infected cells and eliminate reservoirs of infection

Question 19

Phases of the Immune Response

Answer 19

1. Recognition: Naïve lymphocytes recognize corresponding antigen
2. Activation: Lymphocytes differentiate and start clonal expansion
3. Effector phase. Differentiated lymphocytes initiate microbial elimination
4. Decline: After microbial elimination the
   signal for lymphocyte activation disappears.
   Most of the cells activated by antigen die by a process of programmed cell death (apoptosis)
5. Memory: The remaining cells are memory
   lymphocytes, which may survive for months or years

Question 20

Two signals for activation

Answer 20

Signal 1: Antigen receptor binds antigen
Signal 2: Microbial or innate immune signals

Question 21

BCR

Answer 21

B Cell Receptor

Recognizes a distinct microbial 3-dimensional structure

Each recognize a limited number of antigens

Question 22

Clonal expansion

Answer 22

When a BCR or TCR detects antigen the B cell or T cell undergoes multiple rounds of cell division, thereby expanding. Each daughter is identical to the parent cell, i.e. a clone

Question 23

The Memory Phase

Answer 23

Prior exposure to one antigen results in stronger responses to subsequent challenges with the same antigen

Question 24

Naïve B cell

Answer 24

A B cell that has never previously
encountered its target structure

The BCR is restricted to the plasma membrane of the B cell

Activated by antigens and other “second” signals

Question 25

B cell activation

Answer 25

Results in their proliferation (clonal expansion) and differentiation into effector cells that actively secrete antibodies. BCR production is now modified so that the BCR is secreted as an antibody

Question 26

Antibody (Ab)

Answer 26

A secreted BCR from B cells that recognize antigens Released into circulation and mucosal fluids by B cells upon infection Neutralizes microbes and microbial toxins Stops microbes from gaining access to or colonizing host cells. Does NOT have access to intracellular microbes

Question 27

CD4+ helper T cells

Answer 27

They detect antigens presented by professional Antigen Presenting Cells They secrete cytokines to activate other components of the immune response (Macrophages, B cells etc.)

Question 28

CD8+ cytolytic T cells

Answer 28

They detect microbial antigens presented by all nucleated cells and destroy the presenting cell

Question 29

The Lymphatic System

Answer 29

A network that transports fluids from tissues through lymph nodes and then to the circulatory system. Excess interstitial fluid is collected by the lymphatic system and is processed by lymph nodes, then deposited into the circulatory system. Unlike the circulatory system, the lymphatic system is not closed and has no central pump

Question 30

Lymphatic System Processes

Answer 30

1. Some APCs drain from peripheral tissues into lymph nodes. 2. T lymphocytes enter lymph nodes. 3. APCs activate T Lymphocytes 4. Lymphocytes exit lymph nodes and enter circulation, then exit circulation into inflamed tissue where they mediate microbial destruction

Question 31

Lymph node

Answer 31

A secondary lymphoid organ with regions that are rich in certain cell types Components: - Afferent lymphatic vessels (for entry) - Cortex (B cell rich) - Paracortex (T cell and DC rich) - Medulla - Efferent lymphatic vessel (for exit)