ANTIBODIES B2L1 PART 1

What are antibodies?

Proteins produced by the immune system.

What cells secrete antibodies?

B cells

When is the antigen marked for disposal/degradation?

After the antibody binds the antigen

Types of stem cells that come from blood stem cells

Myeloid and lymphoid stem cells

What do myeloid stem cells produce?

• Myeloblast

• Platelets

• RBCs

Types of granulocytes made by myeloblast

• Eosinophil

• Basophil

• Neutrophil

Types of cells made by lymphoblast

• B lymphocyte

• T lymphocyte

• Natural Killer Cell

When are B cells activated?

Once the antigen is presented to it

B-cell activation steps

1. Virus produces antigen

2. Antigen is presented to B cell

3. B cell is activated

4. Lymphoblast is created, differentiation into memory B cell or B cell

5. B cell becomes plasma cell

6. Plasma cell makes antibody

Neutralization

Antibodies bind directly to pathogens and block them from interacting with host cells.

How Neutralization works:

Antibodies cover viral surface proteins so the virus cannot attach to and enter host cells.

Why is neutralization important?

It makes the pathogen harmless so it can't infect or damage cells.

Complement recruitment

Antibody classes (IgM and IgG) can trigger the complement cascade after binding to an antigen

How complement works:

1.Antigen-antibody complexes activate the classical complement pathway.

2. Complement proteins assemble into the membrane attack complex (MAC) which punches holes in bacterial membranes.

3. Complement fragments (C3a, C5a) also act as inflammatory signals, attracting immune cells.

Opsonization

Antibodies act as a handle for phagocytes to grab onto pathogens

How Opsonization works?

1. Antibodies coat the surface of the pathogen

2. Fc regions are recognized by Fc recptors on phagocytes

3. This binding stimulates engulfment and digestion of the pathogen

Antigen

• substances trigger an immune response in the body

• can be derived from pathogens or non-infectious sources

• triggers immune response, leads to antibody production

Pathogen

• microorganisms or agents that cause diseases in hosts

• causative agents of infectious diseases

• actively invade the host and evade immune defences

What is the main difference between antigens and pathogens?

Pathogens are microorgansims and antigens can be toxic substances.

Immunogenicity

The immune response triggered by antigens

What can cause autoimmune disease?

Non-foreign molecules or substances can become immunogenic, leading to an immune response targeting the immune system

2 Domains the Y shaped fragment of antibodies are divided into

Fab and Fc

Fab

• fragment antigen binding

• region that binds antigen

Fc

• Fragment crystallizable region

• interacts with cell surface receptors

What is the hypervariable region?

The region at the top of the antibody. Allows for hypervariabilitu of potential binding partners or interactions with any potential antigen

What can the hypervariable region be used for?

Can be used in drug development by treating protein of interest as an antigen.

Components of antibody structure

• two hypervariable regions

• two light chains

• two heavy regions

What makes up the constant region of antibodies?

Light + heavy chain

Monoclonal antibody

• binds a single epitope of an antigen

• more expensive and difficult to make

• generated by identical immune cells that are cloned and formed from aa single parent cell

Which region of the antibody interacts with the antigen?

Variable region

Polyclonal antibodies

• Mix of antibodies that bind the same antigen via different epitopes 

• good for knowing if a protein is in a sample or not