Immune System

The immune system defends against threats in our environment

Two types of immunity Innate

which you are born with Acquired

which you develop throughout your life

When faced with a invader your body has: 1st line of defence 2nd line of defence 3rd line of defence

Just like an army

Barriers such as: cilia, HCL, skin and mucous membranes

The skin has acidic secretions which kill bacteria

The mucous membranes secrete: tears, saliva, perspiration All contain lysozyme an antimicrobial

enzyme that destroys the cell walls

It is non-specific It involves:

neutrophils macrophages

Macrophages: engulf invading

organisms by phagocytosis

display the foreign antigen on their membrane

Neutrophils:

are attracted to a signal damaged cells give off and migrate towards them

engulf the microbe and macrophage

Release lysosomal enzymes to digest both (microbe and macrophage)

What remains?

Fragments of proteins, dead WBCs, dead microbe = PUS

The damaged tissue initiates a inflammatory response….. redness, swelling and pain (this is to keep you from using the damaged tissue)

Now things are more serious…… the third line of defence is initiated

This is very specific

Complement proteins (serum proteins) aggregate to initiate an attack on the cell membranes of fungal or bacterial cells

1st group seals invader

2nd group punctures wall

3rd group attaches to the invader to attract leukocytes

T cells: contain the blue prints for antibodies They roam the body and search for

invaders signal the attack

Remember : The Macrophages that engulfed bacteria display the antigen on their outer membrane

Helper T then does 2 things:

it activates the killer T cells (these lymphocytes search and destroy)

Helper T cells read the antigen’s shape (the blue print) and release lymphokine

Lymphokine (chemical messenger) targets B cells

The B cells receive the information about the invader

B cells multiply and produce antibodies (weapons) ....they display these on their membrane

antibodies : are Y-shaped proteins that bind to specific antigen markers on other cells

Antigens: are protein markers that are found on the cell membranes of most cells

When our antibodies attach to the antigen markers, they form a antigen-antibody complex

it ties up invaders so they can’t damage our cells

the antigen-antibody complex is really large making it easy to be found by macrophages

Macrophages will engulf and destroy the complex

suppressor T cells inhibit the immune response (stop it)

the immune system makes memory B &T cells

These cells are to recognize the invader if it returns

Macrophages: any of the large phagocytic cells some are fixed and some circulate in the

blood stream

B-cells – plasma (make antibodies), memory

T-cells – helper, killer, suppressor, memory

Specialized receptor sites are found on the cell membrane of different cells They are the site which hormones and nutrients

enter the cell

Toxins with a similar shape to a hormone or nutrient can attach to the receptor site

It then becomes engulfed by the cell

use receptor sites as entry ports

They inject DNA material into the cell but leave their protein coat at the receptor site There protein coat enable them to attach to

certain cells

E.g. HIV infects T cells