Lecture 2 - Cells and Tissues of the Adaptive Immune System

Question 1

__________ are the main immune cells of the humoral adaptive immune system and __________ are the main immune cells of the cell-mediated adaptive immune system.

L2 S4-6

Answer 1

B lymphocytes -> humoral

T lymphocytes -> cell-mediated

Question 2

What common cell type do T cells and B cells develop and mature from and where do they do so?

L2 S4+21-23

Answer 2

Both stem form lymphoid progenitor cells which migrate to primary lymphoid organs, the thymus (T cells) or bone marrow (B cells), to develop and mature.

Question 3

Describe the humoral adaptive immune system.

L2 S5

Answer 3

• B lymphocytes express extracelluar receptors which could potentially recognize Ags
• if extracellular receptor do recognize an Ag, the cell produces Abs based on the receptor which are secreted into the blood or mucosa
• Abs bind Ags which neutralizes infectivity and targets for elimination
• Ags can either be part of EXTRACELLUAR MICROBE or their TOXINS

Question 4

Describe the cell-mediated adaptive immune system (CMI).

L2 S6

Answer 4

• T lymphocytes recognize Ags from Ag-presenting cells and phagocytes
• instruct cells presenting microbial antigens to kill phagocytized INTRACELLULAR microbes (macrophages) or under apoptosis to kill INTRACELLULAR infecting microbes

OR

• helper T cells activate macrophages that have phagocytized microbes (INTRACELLULAR) and present Ags causing them to kill them
• cytotoxic T cells destroy cells infected by INTRACELLULAR microbes which present Ags

Question 5

Who is the father of humoral immunity and what did he do?

L2 S8

Answer 5

Paul Ehrlich

• postulated about the existence Ags
• coined the term “antibody”
• developed a theory that said that hosts for a defense against substances present in body fluids (precursor to current humoral theory of immunity)

Question 6

Who is the father of cell-mediated immunity and what did he do?

L2 S9

Answer 6

Elie Metchinkoff

• discovered macrophages and postulated their function in the immune system
• although he was unable to prove it, his beliefs led to the cell-mediated theory of immunity)

Question 7

What is the clonal selection hypothesis?

L2 S11-13

Answer 7

• varying Ag-specific lymphocytes develop BEFORE exposure to Ags
• when exposed to Ag that they are specific for, they are induced to proliferate and differentiate
• specific antigen is eliminated by the lymphocytes that were selected for
• after infection, surviving cells become memory cells

Question 8

What are the phases of adaptive immune response?

L2 S14

Answer 8

Antigen recognition:
-naïve lymphocytes recognize antigen

Lymphocyte activation:

• lymphocytes proliferate (clonal expansion)
• lymphocytes differentiate (start secreting antibodies or become effector T cells)

Antigen elimination

Contraction:
-expanded population of lymphocytes is reduced to normal level by apoptosis

Memory:
-cells that do not undergo apoptosis become memory cells

Question 9

Differentiate between primary and secondary adaptive immune response and explain what is responsible for the difference.

L2 S16

Answer 9

Primary adaptive immune response:

• Ag is recognized by undifferentiated, naïve lymphocyte and must differentiate before eliminating Ag
• differentiated cells that remain after infection become memory lymphocytes

Secondary adaptive immune response:

• Ag is recognized by already differentiated, memory lymphocyte
• memory lymphocyte produces a stronger, more rapid response than naïve lymphocytes did in primary response
• subsequent responses will be even stronger

Question 10

Differentiate between active and passive immunity.

L2 S18

Answer 10

Active immunity:

• developed by host due to exposure to Ag (either vaccination or infection)
• host responds by developing Abs for Ag
• memory of Ag is formed

Passive

• conferred by transfer of Abs or T lymphocytes from another source
• no memory of Ag is formed

Question 11

What are the different classes of lymphocytes and what are their functions?

L2 S20

Answer 11

B lymphocytes:
-recognize soluble Ags and develop into Ab secreting cells

Helper T lymphocytes:
-recognize Ag on Ag-presenting cells and secrete cytokines in response

Cytotoxic T lymphocytes:
-recognize Ags on infected cells and induce apoptosis

Regulatory T lymphocytes:
-suppress and prevent immune response to self-antigens

Question 12

Why are most T cells produced early in life?

L2 S26

Answer 12

The thymus begins to shrink following puberty and is gradually replaced by fat and connective tissue.

Without the thymus, new T cells cannot develop

Question 13

What do CD4 and CD8 refer to?

L2 S28

Answer 13

Helper T cells express the cluster of differentiation CD4, while cytotoxic T cells express CD8

Question 14

T cells which are specific to self antigens are depleted by apoptosis. It would be really bad for you if they didn’t.

Answer 14

Just know this

Question 15

What change occurs in the location of B cell development in an organism?

L2 S31

Answer 15

As a fetus, B cells mature in the liver, after birth they develop in the bone marrow.

Question 16

What cells and factors in the thymus and bone marrow guide T cell and B cell differentiation respectively?

L2 S27;31

Answer 16

Thymus/T cells:

• specialized epithelium
• dendritic cells
• macrophages

Bone marrow/B cells:
-stroma

Question 17

In what parts of the body do leukocytes not circulate?

L2 S34

Answer 17

• eye
• brain
• testicles

Question 18

How do naïve lymphocytes enter secondary lymphoid organs (lymph nodes)?

Answer 18

High endothelial venules

Question 19

By what process do lymphocytes transmigrate from the blood into tissue? What stimulates this?

L2 S34

Answer 19

Diapedesis which is stimulated by chemokines.

Question 20

By what process are B cells activated and what do they do once activated?

L2 S27

Answer 20

Naive B cells migrate to secondary lymphoid tissues. If exposed to Ags, they become activated and mature to memory cells or plasma cells.
Plasma cells function to produce and secrete Abs.

Question 21

By what process are T cells activated and what do they do once activated?

L2 S42

Answer 21

Naive T cells migrate into secondary lymphoid tissues. If exposed to Ags they differentiate into effector or memory T cells. Some cells migrate to peripheral site of infection while other remain in secondary lymphoid tissue to help activate B cells

Question 22

Where are B cells and T cells located in a lymph node? What causes them to migrate to different regions?

L2 S43-44

Answer 22

B cells aggregate in the B cell zones (follicles), just deep to the capsule.

T cells aggregate in in the T cell zones, just deep to the capsule but superficial to the medulla.

Chemokines specific to each cell type release from the different zones are responsible for the segregation.

Question 23

How do activated antigens and non-naïve lymphocytes enter a lymph node?

L2 S43

Answer 23

Afferent lymphatic vessels

Question 24

What types of cells can be antigen presenting cells.
What do these antigen presenting cells do?

L2 S47

Answer 24

Cell types:

• dendritic cells
• macrophages
• activated B cells

Function:

• capture, process and display Ags to activate T lymphocytes
• signal for proliferation and differentiation of lymphocytes

Only dendritic cells can activate naïve T cells.
Dendritic cells and macrophages are part of innate immune system and link to acquired immune system.

Question 25

What are the types of dendritic cells and where are they derived from?
What do they do?

L2 S49

Answer 25

Stem cell derived:

• classical dendritic cells
• lasmacytoid dendritic cells
• Langerhans cells

Monocyte derived cells:
-myeloid dendritic cells

Functions:

• acquire Ags via endo/pinocytosis
• present Ags
• secrete cytokines