An Overview of Human Immunity

Question 1

Primary function of immune system

Answer 1

To provide host defence against invading pathogens

Question 2

Components of immune system

Answer 2

Immune system is broken down into >>

• Innate immunity
• Adative immunity

​Adaptive immune system is further classified in to >>>

• Humoral
• Cell mediated

Question 3

What is the difference between innate immune response and adaptive immune response?

Answer 3

Innate immune response >>>

• Rapid response to pathogens
• Non-specific
• Lacks any memory

Adaptive immune response >>>

• Takes longer time to respond to pathogens
• Highly specific
• Lasting memory exists

Question 4

Cells of innate immunity

Answer 4

• Antigen presenting cells (APCs), e.g. Dendritic cells
• Macrophages
• Mast cells
• Granulocytes: Neutrophils, Eosinophils, Basophils
• Complement proteins
• NK cells (Natural killer cells)

Question 5

Cells of adaptive immunity

Answer 5

• B-lymphocytes >>> produces Ig
• CD4+ T lymphocytes (Helper T cells)
• CD8+ T lymphocytes (Cytotoxic T cells)
• NK cells (Natural killer cell)

Question 6

Cells of humoral immunity

Answer 6

• B-lymphocytes

Question 7

Cells of cellular immunity

Answer 7

T lymphocytes

• Cytotoxic T cells (CD8+)
• T helper cells (CD4+)

Question 8

Common cell between innate and adaptive immunity

Answer 8

NK cell = Natural Killer cell (one type of T lymphocytes)

Question 9

How do the different components of immune system act, in isolation or in concert?

Answer 9

All the components act in concert

Vast array of communication networks (comprising chemokines, cytokines) enables crosstalk between the different cells

Question 10

Basic steps of human immune defence

Answer 10

When a pathogen invaes into the body >>> innate immunity kicks in >>> phagocytes (macrophages) engulf or destroy it

If it fails to do so, APC (e.g. dendritic cells) or macrophages will present the antigen of the pathogen to T cells of adaptive immunity >>> Adaptive immunity kicks in

>>> T cells recognise it & differentiates into cytotoxic T cells (T killer cells) OR helper T cells

>>> Cytotoxic T cells destroy the pathogens

>>> OR helper T cells >>> activate B lymphocytes >>> B cells produce antibodies (immunoglobulins) >>> Ag-Ab reaction >>> destroy pathogen

Question 11

Why does the 2nd time invasion resolve more quickly than the 1st time invasion?

Answer 11

Because, after first time invasion >>> formation of memory cells (comes from adaptive immunity, mainly T lymphocytes)

Question 12

Consequences after 1st exposure

Answer 12

4 Possible consequences:

• First exposure >>>>> death
• First exposure >>>>> innate immunity kicks in >>>>> destroys pathogen >>>>> no disease
• First exposure >>>>> innate immunity kicks in >>>>> needs to activate adaptive immunity >>>>> adaptive immunity fails >>>>> death
• First exposure >>>>> innate immunity kicks in >>>>> needs to activate adaptive immunity >>>>> adaptive immunity destroys pathogen >>>>> no disease >>>>> specific memory of that disease (memory cells)

Question 13

Consequence after second exposure

Answer 13

2 Possible consequences:

• Second exposure >>>>> innate immunity kicks in >>>>> destroys the pathogen >>>>> no disease
• Second exposure >>>>> Innates immunity kicks in >>>>> needs to activate adaptive immunity >>>>> as they have a memory from thier activation in the 1st exposure >>>>> definitely destroys pathogen >>>>> no disease

(usually no fatality here)