Immune system - lect 25

Active Immunity + (natural/artificial)

Your body does the work

Natural → You get sick → body makes its own antibodies

Artificial: Vaccines → stimulate your immune system to prepare defenses

May require booster shots to refresh memory cells

Two types of adaptive immunity

1. Active

2. Passive

Passive Immunity + (natural/artificial)

Immunity thats borrowed

Natural: e.g., antibodies passed from mother to baby via placenta or milk

Artificial: e.g., injection of antibodies for emergency protection (like rabies)

Lymphocytes and types (2)

WBC’s in adaptive immunity

1. B-cells

2. T-cells

B-cells (origin, mature in, function, defend against)

1. Bone Marrow

2. Bone Marrow

3. Create Antibodies

4. Pathogens in blood/body fluids

T-cells (origin, mature in, function, defend against)

1. Bone Marrow

2. Thymus

3. Attack Infected cells

4. Pathogens already inside cells

Antigen (Antibody generator)

A foreign molecule (like part of a virus, bacteria, or toxin) that triggers a response from B or T cells.

• Usually proteins or polysaccharides

• Found on the surface of pathogens

Epitope

The specific region of the protein on the antigen that a receptor or antibody binds to (think of it like a puzzle piece fitting perfectly).

Antibody

• Defense protein made by B cells

Also called immunoglobulin (Ig)

Binds to antigens to help neutralize or destroy them

B & T Cell Diversity

Your body can make over:

• 1 million types of B cell receptors

• 10 million types of T cell receptors

This means you can recognize almost any invader

Self-Tolerance

Your immune system learns to ignore your own cells

If this fails → autoimmune disease

Immunological Memory (long term protection)

Primary Response

Secondary Response

Primary Response (Immunological Memory) (how long last?)(cells fighting)

First time you’re exposed to virus

• Slower (10–17 days)

• Effector cells fight infection

Secondary Response (Immunological Memory) (how long last?)

Second exposure to virus

• Faster (2–7 days), stronger, and longer lasting

Why? → Memory cells are already ready to go

This is why you usually get most diseases only once

Clonal selection

When a B or T cell recognizes its antigen, it is activated and divides many times to make:

1. Effector cells

2. Memory cells

Effector cells

Actively fight the infection right away

Memory cells

Stay in your body for years to respond faster next time

B-cells Receptor Shape

Y-shaped

B-cells Make antibodies?

Yes – antibodies = immunoglobulins

B-cells Target

Pathogens in body fluids (blood, lymph)

B-cells Receptor Binds To

Antigen on free pathogens → many antibodies made

V (variable) region

The part of the B cell receptor (BCR) that binds to antigens

T Cells Receptor Shape

NOT Y shaped

T-cells Make Antibodies?

No - antibodies

T-cells Target

Your own infected cells

T-cells Receptor (TCRs) Binds To

ONLY Antigen fragments displayed on other cells (APC’s and infected cells)

Antigen-Presenting Cells (APCs)

Cells that eat invaders and show their fragments so that TCR can bind to the antigen fragments (Ag)

Infected body cells

A virus-infected skin or lung cell, showing a “warning” piece of the virus.

Helper T-cells - Response to Antigen

1. APC displays antigen fragment

2. This type of cell binds to APC and calls for help from

   a. Cytotoxic T-cells and B-cells

Cytotoxic T-cells

Kills infected host cells displaying antigen

Helper T-cells Responses (2)

1. Cell-mediated Response

2. Humoral Response

Cell-Mediated Response

This response “mediates” protection by killing sick cells directly.

Target: Your own infected cells (like virus-infected or cancerous cells)

Main Player: Cytotoxic T-cells (aka “killer T-cells”)

What happens:

Helper T-cells release cytokines (signaling molecules)

These cytokines activate cytotoxic T-cells

Activated cytotoxic T-cells search for infected cells and kill them

Humoral Response

This response deals with threats that are still outside of cells — bacteria, viruses before entry, etc.

Target: Pathogens floating in body fluids (blood, lymph)

Main Player: B-cells

What happens:

Helper T-cells help activate B-cells

Activated B-cells produce antibodies

Antibodies bind to invaders in blood, marking them for destruction

Cytokines

Signaling molecules released by Helper T-cells

Response to antigen Summary

Antigen fragments (Ag) display on an APC → Helper T-cell → binds to APC → binding produces cytokines and autocrine and paracrine signaling → cytokines trigger → cytotoxic t-cells (cell mediated) and b-cells (humoral)

Cytotoxic T-cells (Killer T-cells) Role

Destroy your own infected or cancerous cells

Cytotoxic T-cells (Killer T-cells) Type of Response

Cell-mediated immunity - activated by T-cells

Cytotoxic T-cells (Killer T-cells) Mechanism

Once activated, they release proteins to kill the target cell:

1. Perforin: Punches holes in the infected cell’s membrane

2. Granzymes: Enter through those holes and trigger apoptosis (programmed cell death)

This kills the infected cell before the pathogen can replicate further.

Perforin (protein by killer t-cells)

Punches holes(pores) in the infected cell’s membrane

Granzymes

enter through holes made by perforin and Initiate apoptosis - programmed cell death

B-cell and Antibodies activation (3 steps)

1. B-cell binds to a matching antigen (Ag)

2. With help from Helper T-cells, B-cell gets fully activated

3. Then it divides (proliferates) and makes antibodies

Complement System

Works with antibodies to kill pathogens more effectively (complements the antibodies)

Complement System Functions (2)

1. Neutralization

2. Opsonization

Neutralization (Complement system)

Antibodies bind to virus surface → virus can't enter host cells

Opsonization

Antibodies coat bacteria → makes them easier for phagocytes to “eat”

Vaccines facts (3)

1. Build resistance

2. Use variant/derivative of pathogen

3. Harmless, stimulates immune response

Types of vaccines

1. Live attenuated

2. Inactivated

3. Subunit

4. DNA

Live Attenuated Vaccine

Weakened infection organisms that stimulate an immune response without causing disease.

example: Polio(sabbin vaccine), yellow fever, smallpox

Inactivated Vaccine

Killed pathogens

example: Polio(Salk ), rabies, pertussis

Subunit Vaccine

Just pieces of the pathogen

example: influenza type B

DNA Vaccine

Injection with genetically engineered DNA that produce an antigen (vertinary use only at present)