First and second line of defence - Immunology

First line of defence

A component of the innate immune system and provides a non-specific and rapid form of protection against pathogens. Examples of these defences include physical, chemical, and microbiological barriers.

Physical barriers for plants

Waxy cuticles of leaves

Closing stomata to prevent pathogens invasion during C02 intake

Thick bark

Thorns to deter insects

Examples of each first line defence barrier

Physical barrier - sense organ - ear wax, hairs, eyelashes, nostril hair which traps pathogens

• Intact skin

Chemical barrier - Digestive system - lysozymes in saliva and mucus breaks down pathogen as well as enzymes in stomach acids as it has (low ph )

Microbiological barrier - normal flora compete with pathogenic bacteria for space and resources in the gastrointestinal tract/small intestines, potentially challenging their survival and preventing them from thriving and causing infection.

Innate immunity

The inborn ability of an organism to protect itself against pathogens.

Autoimmune disease

A disease in which an individual’s immune system initiates an immune response against its own cells 

Second line of defence

Non/specific also a part of the innate immune system

Antigens

Antigens are molecules that are recognised by the immune system as either non-self foreign or self or allergens.

Describe the role of self-antigens in our immune response.

Are molecules on the surface of cells that marks the organism as “self” so that the immune system doesn’t attack them. They all have MHC - Class 1.

Non-self antigen

Antigens that the immune system reads as “foreign” or not belonging to the individual. Have MHC - Class 2.

Phagocytes

Consume and destroy foreign or dead material present in the body by engulfing it through the process of endocytosis. The foreign material is destroyed by fusing it with a vesicle containing lysozyme.

• Three types are Macrophages, Neutrophils - don’t present antigen, Dendritic cells

Steps of phagocytosis

1 - Phagocytes comes in contact with bacteria

2 - Phagocytes develops indents in its plasma membrane around the bacteria and engulfs the bacteria.

3 - Bacteria placed into a vesicle called a phagosome.

4 - Phagosome combines with lysosome to become phagolyzosome, which now contains enzymes and low pH that destroys the bacteria.

Fragments of the phagocytes present on the MHC - 2 (ON IMMUE CELLS) with the antigens ( if phagoctyes is specific)

Macrophages and Dendritic cells are also called?

Antigen - presenting cells that can consume and destroy foreign material but also present antigens from the consumed material on their surface.

Antigen presenting cells

Specific immune cells which also has MHC class 2 using them to present the consumed antigens on their surface.

MHC Class 2 + Antigen to activate the adaptive immune system.

MHC - Class 1

Proteins on the surface of all nucleated cells in the body (not red blood cells).

• When it is infected, it has non-self antigen on its MHC - Class 1 so immune cells like cytotoxic T cells can destroy it.

What happens if a cell doesn’t have MHC - class 1?

Natural killers cells will identify and destroy infected or damaged cells.

How can virus avoid being detected so it wouldn’t be destroyed?

Virus can infect cells and prevent it being destroyed by cytotoxic T cells by having the cell have no MHC - Class 1. Infected cells is now invisible to the immune cell except for natural killer cells.b

Natural killer cells

Responsible for the destruction of abnormal/damaged or infected cells (cells that don’t present MHC Class 1 )

- They only work by looking if cells have MHC - Class 1 or not.

• Recognise there is no MHC - class 1

• Release cytotoxic chemicals that disrupt the infected cell’s membrane

• Triggers apoptosis

• They have a inhibitory receptor - stops the natural killer cell to kill the cell. because there is MHC -1 cells

• The activation receptor - kills the cell

Mast cells (second line defence)

Are in the connective tissue (near the surface of the skin) and they detect injury to surrounding cells or any stimulated by allergens.

• When they are activated they release histamine (the process is called degranulation), a signalling molecule that plays an important role in the inflammatory response and allergic response

Eosinophil cells (second line defence)

Responsible for destroying large multicellular parasites by releasing cytotoxic chemicals.

Defensive molecules

• Involved in both the innate and adaptive immune response

• Complementary protein when activated, result in enzyme triggers reactions that lead to lysis of invading pathogens

• Cytokines (many different proteins )

  • signalling molecule

Complement proteins

Proteins in the blood that help the immune response. The activation leads to a complement cascade, when the complement protein stick on the outside surface of pathogens

How are pathogens destroyed using complement proteins

Opsonisation - Complement proteins stick on the outside surface of pathogens. So cells of the immune system can easily recognise it as foreign

Chemotaxis - Phagocytes - macrophages, dendritic or are attracted to the complement proteins and pathogens making the (pathogen) likely to be destroyed.

Lysis - Complement proteins join together on the surface of pathogens, forming a MAC (membrane attack complex), which creates pores in their membrane. Destroys the pathogen by causing lysis (via the sudden influx of fluid into the pathogen, causing it to burst. )

Interferons

Produced by virus-infected cells

•Prevent entry of virus to nearby cells.

•Attract and activate NK cells to destroy the virally infected cell

•Some viruses can inhibit production of interferons

Chemokines

Chemical attractants

•Attract leukocytes to sites of infection and inflammation

Fever

Inflammation is the accumulation of plasma proteins (complement proteins and cytokines) and leukocytes that occurs when tissue is damaged or infected.

Fever is triggered by inflammatory cytokines.

•Slows replication of bacteria and viruses

•Increases activity and proliferation of leukocytes

The Inflammatory response

Inflammatory response increases blood flow to an injured area, bringing a greater number of immune cells and components to help clear debris and fight pathogens.

There are three steps to the inflammatory response –
initiation, vasodilation and migration.

Initiation

Breach in the first line of defence causes injured cells to release cytokine to mast cells. Mast cells release histamine

Vasodilation

Histamine released from the mast cells causes vasodilation. This causes blood vessels become more permeable. - Vessels widen

• widen vessels = more blood = redness + heat

• permeable walls = fluid leaks into membrane= swelling + pain

Migration

Immune cells and phagocytes leave the blood vessel as they are attracted to the site of injury by the complement protein. The complement proteins are attached to the pathogen so phagocytes can destroy it? Platelets travel to the wound and stop active bleeding.