Immune System Notes

the three lines of defense in the human body

Surface barriers, innate immunity, adaptive immunity

two major branches of the immune system

Innate (fast, nonspecific) Adaptive (specific, memory)

What is the main purpose of surface barriers?

Prevent pathogens from entering the body

Physical surface barriers

Skin, mucous membrane

Mechanical removal barriers

Tears, saliva, mucocilliary escalator

Chemical and biological barriers

Stomach acid, skin acidity, urine acidity, commensal bacteria

What makes innate immunity “innate”?

It responds immediately and the same way to all pathogens

What are Toll-like receptors (TLRs)?

receptors that recognize general pathogen associated patterns

What cells are the main phagocytes?

Neutrophils and macrophages

What do neutrophils do?

Arrive first and rapidly engulf pathogens; short-lived

What do macrophages do?

long lived phagocytes that also present antigens to T-cells

What do natural killer (NK) cells do?

targeted death of infected host cells, induce apoptosis through leaky membranes, innate immune response

What does the complement system do?

forms the membrane attack complex to burst pathogens

What do antimicrobial peptides do?

damage or puncture microbial membrane

What causes inflammation?

release of histamine and cytokines

what are the effects of histamines?

vasodilation, leaky capillaries, increase blood flow

What is the purpose of inflammation?

concentrate immune response at the site of infection

What makes adaptive immunity different from innate immunity?

it is specific and creates memory for future responses

What cells are responsible for adaptive immunity?

B-cells and T-cells

What cells are responsible for adaptive immunity?

B-cells and T-cells

Where do B cells and T cells mature?

B-cells in the bone marrow and T-cells in the thymus

What do B-cells do?

produce antibodies to target extracellular pathogens

What do T-cells do?

kill infected cells or help activate other immune cells

What is an antigen?

any molecule that triggers an adaptive immune response

What is an epitope?

portion of an antigen that binds the antigen receptor

How do B and T cells generate millions of unique receptors?

DNA recombination (random V,J, C segment mixing)

What is self tolerance?

elimination of self-reactive lymphocytes to prevent autoimmune disease

What is clonal selection?

when a lymphocyte encounters its matching antigen, it is activated to divide

What are the two types of cells created during clonal expansion?

effector cells (fight NOW) and memory cells (long-term immunity)

What activates B-cells?

antigen binding + helper T-cell interaction

what do activated B-cells produce?

Antibodies

What are the three main functions of antibodies?

Neutralization, opsonization, activation of complement

What is neutralization?

antibodies bind to antigen and make it impossible for them to invade cells

What is opsonization?

antibodies bind to an antigen and facilitate macrophagy/phagocytosis

what must happen for a T-cell to be activated?

antigen must be presented ON an MHC molecule

What does MHC I activate?

Cytotoxic T-cells CD8

What do MHC II activate?

Cytotoxic T-cells MD4

What do cytotoxic T-cells do?

kill infected host cells using perforins and granzymes, adaptive immunity,

What do helper T-cells do?

Activate B-cells, cytotoxic T-cells, and macrophages

How do primary and secondary immune response differ?

Primary = slow and weak Secondary = fast and strong due to memory cells

What is active immunity?

Your body produces its own immune response (infection or vaccine)

What is passive immunity?

You receive antibodies directly (breast milk, antivenom)

What is antigenic variation?

when pathogens alter surface epitopes to avoid detection

What is antigenic drift?

small, slow mutation in pathogen coat proteins

What is antigenic shift?

Large gene swaps that create new strains

How does HIV escape the immune system?

kills helper T-cells, mutates rapidly and hides in host genome (latency)

What is AIDS?

immune system collapse caused by severe loss of helper T-cells.

Phagocytosis

1. when an immune cell EATS a pathogen.

2. removes bacteria,

3. cleans up dead cells

4. presents pieces of the pathogen to T-cells later.

Lymphocytes

the main white blood cell of the adaptive immune system

What are the effects of cytokines?

attract/activate other immune cells

What is the maturation process and why is it important?

self reactive lymphocytes are removed during maturation, important because autoimmune diseases will otherwise form