L05 – Introduction to the Immune System

Question 1

List the primary lymphoid organs and their function?

Answer 1

Bone marrow, Thymus

Provide appropriate microenvironment for lymphocytes to develop from lymphoid stem cells and proliferation + mature

Question 2

List the secondary lymphoid organs and their function?

Answer 2

Spleen
Lymph nodes
Mucosa- associated lymphoid tissues (MALT) i.e. Tonsils, Peyer’s patches in ileum

Provide appropriate microenvironment for lymphocytes to interact with antigens, accessory cells

Question 3

Distribution of immune cells in body?

Answer 3

 Circulating cells in blood, lymph

 Anatomically defined collections in lymphoid organs

 Scattered cells in virtually all tissues

Question 4

Outline the general functions of lymphocytes? Sites of maturation?

Answer 4

Recognize and respond to foreign antigens and provide immune specificity

B lymphocyte:

• Bone marrow development
• diff. into memory B cells or Plasma cells to produce Ab, immunological memory

T lymphocytes:

a) CD4 Helper: secrete cytokines, interact with B cells, macrophages
b) CD8 Cytotoxic: direct cytotoxicity to target cells
- BM origin with Thymus maturation

NK cells: 15% of lymphocytes with neither B or T antigen, recognize and kill tumour cells

Question 5

List types and functions of Accessory cells?

Answer 5

• Mononuclear phagocytes: Monocytes, Macrophages: phagocytose pathogens, senescent cells and chemotaxis response (i.e. cytokines)
• Antigen-presenting cells (APC): macrophages, B lymphocytes and dendritic cells: immunostimulatory capacity by presenting antigens to T and B cells

Question 6

What is the most potent APC? Function (3)?

Answer 6

Dendritic cells

1) Activate B cell to diff. into plasma cells&raquo_space; Ab secretion
2) APC to Cytotoxic T cell > lysis of infected cells
3) APC to T Helper > Secretion of cytokines to activate B and T cells

Question 7

List the 2 immune mechanisms.

Answer 7

1. Non-specific (innate / natural) immunity
2. Specific/ adaptive/ acquired immunity

Bridged by dendritic cells (can activate B cells, T cells etc.)

Question 8

Basic pathogenesis of SLE?

Answer 8

Systemic lupus erythematosus

Impaired clearance of apoptotic cells
> Cells become secondary necrotic and release danger signals
> Inflammation and release autoantigens
> Autoimmune reaction with loss of tolerance

Question 9

List the components of Innate immunity?

Answer 9

 Physical barriers

 Phagocytic cells / phagocytes
 Neutrophils
 NK cells

 Various molecules i.e complement system

Question 10

What is the common connection between Anemia and SLE?

Answer 10

Impaired clearance of cells with oxidative damage/ cellular senescence

Question 11

Compare the specificity, sensitivity and time span of Innate and adaptive immunity?

Answer 11

Adaptive:

• Specific Ag recognition
• Response enhanced after successive exposure to Ag
• Acquired during life, induced by exposure to Ag

Innate:

• Non-discriminatory against most Ag, rely on pattern recognition (Toll-like receptor, Scavenger receptor)
• Not enhanced by succesive exposure
• Present at birth

Question 12

Distinguish Humoral immunity and cellular immunity?

Answer 12

2 divisions of Specific Immunity based on the components:

1) Humoral = Mediated by substances in the cell-free portion of the blood: e.g. Ab (secreted by B lymphocytes)

2) Cellular = Mediated by cells in immunized person:
e. g. T lymphocytes

Question 13

Phases of specific immune response?

Answer 13

Recognition
Activation
Reaction

Question 14

What confers the recognition phase in specific immunity?

Answer 14

Lymphocytes recognize and bind to Ag with specific receptors:

EPITOPE = antigenic determinant, immunologically active region on Ag recognized by both B and T cells

Question 15

What confers the Activation phase in specific immunity?

Answer 15

all lymphocytes undergo 2 major changes:

1) Proliferation (clonal expansion)

2) Differentiation into 2 types of lymphocytes:
a) Effector cells (e.g. plasma cells for B cells)
b) Memory cells

Question 16

What confers the Reaction phase in specific immunity?

Answer 16

Effector cells eliminate Ag

i.e. Plasma cells secrete Ab

Question 17

List the 5 features of specific immune responses?

Answer 17

• Specificity
• Discriminate self/ non-self
• Immunological memory
• Self-regulation
• Diversity

Question 18

How is specificity achieved in specific immunity?

Answer 18

B, T lymphocytes express membrane receptors that distinguish differences between distinct antigens

immune responses = specific for distinct antigens

Question 19

How is diversity achieved in specific immunity?

Answer 19

Gene rearrangement = generate numerous clones of lymphocytes that can discriminate large number of Ag

Question 20

How is memory achieved in specific immunity?

Answer 20

exposure of immune system to a foreign antigen enhances its ability to respond to that antigen

secondary immune responses are usually more rapid, stronger

Mediated by memory B cells

Question 21

How is self-regulation achieved in specific immunity?

Answer 21

All immune responses return to normal after antigenic elimination

Question 22

Name one disease caused by defective immune regulation?

Answer 22

Canale-Smith syndrome

Fas-gene mutation (fas+/-)

> > Elevated levels of Igs (hyper-gammaglobulinemia) and Failure of lymphocytic apoptosis
Increase in number of lymphocytes (5-20 fold)

Lymphadenopathy, splenomegaly

Question 23

Define immune tolerance?

Answer 23

Discrimination of self from non-self:

Lymphocytes recognize and respond to foreign antigens but are normally unresponsive to the self antigens

Question 24

Define the stages of Clonal selection theory.

Answer 24

1. Immunocompetent T or B cell express surface receptor for single Ag epitope
2. Exposed to Ag, epitope on Ag binds to specific cells with matching receptor > Clonal selection
3. Specific binding of epitope to BCR/ TCR induces proliferation of these lymphocytes into clones with the same receptors > Clonal expansion
4. B cells mature into plasma cells secreting antibodies with the same specificity as the surface receptors on the parent B cell
5. Some clone cells generated become “memory cells” with same antigen specificity.
6. Removal of antigen-specific clones will result in antigen-specific non-responsiveness i.e. tolerance.

Question 25

Difference in antigen removal between early and late adaptive immune response?

Answer 25

Early: 4-96 hours: Infection > Recruitment of effector cells > recognition, activation > Removal of AG

Late: >96 hours : Infection > transport of Ag to lymphoid organ** > Recognition by naive T and B cells > Clonal expansion and differentiation of effector cell** > removal of Ag