7. Recognition of Antigens

Question 1

What are antigens?

Answer 1

Compounds foreign to the body that trigger an immune response.

Question 2

What epitopes?

Answer 2

The surface of a pathogen may have several different types of antigens sometimes referred to as epitopes?

Question 3

What does the plasma membrane of an immune cell carry?

Answer 3

• self antigens that identify the immune cell as self
• receptors for self antigens so that this cell can identify and not attack other body cells
• receptors for foreign antigens so that the immune call can identify forge in material and signal other immune cells to eliminate it

Question 4

How are cells of the body identified as self by the immune system?

Answer 4

• protein markers on the surface of the cell membrane
• these markers are expressed due to information contained in the nucleus/genes
• the group of genes that determine these protein markers is called the major histocompatibility complex MHC or human leukocyte antigen HLA

Question 5

Are protein markers unique to individuals?

Answer 5

As the markers are determined by the genetic makeup of an individual they are unique to that individual.
The closer the individuals are related the closer their antigens will be.

Question 6

Which MHC markers are found where?

Answer 6

MHC class I markers found on all cells except red blood cells
MHC class II markers found on antigen presenting cells (macrophages for instance)

Question 7

What are antigen presenting cells?

Answer 7

Cells that process foreign antigens, placing them on their cell membrane to present to other cells of the immune system, stimulating an immune response.

Question 8

What is the difference between MHC and HLA?

Answer 8

-MHC is found in many vertebrates while HLA is found in humans

Question 9

What are pathogens?

Answer 9

Pathogens are disease causing organisms or agents

Question 10

Are infections and diseases the same?

Answer 10

If pathogens can gain entry to the human body and reach the target cells the pathogens may multiply rapidly and produce and infection
If the body’s immune system cannot overcome the infection then the infection will develop into a disease. An infection is a necessary precondition to a disease.

Question 11

What is a disease?

Answer 11

Any condition that impairs the normal activity of an organism.

Question 12

What is an infection disease?

Answer 12

A disease caused by a pathogen and can be passed from one organism to another.

Question 13

What is a non infectious disease?

Answer 13

A disease not caused by a pathogen and cannot be transmitted directly from one person to another.

Example is inherited genetic disorder, nutritional deficiency,autoimmune disease (results from the immune system failing to properly detect its own cells (self) from those of other organisms (non self)).

Question 14

Examples of non infectious disease

Answer 14

Inherited, genetic disorder
Nutritional deficiency 
Autoimmune diseases
Cancer
Social
Congenital (passed from mother to baby in the womb or during development)

Question 15

How are infectious diseases passed from one person to another?

Answer 15

Body contact
Sexual contact
Food and water
Droplet or airborne 
Carrying vector 
Injecting vector
Indirect contact

Question 16

What can the symptoms of a disease result from?

Answer 16

Physical or chemical damage to the host organism

An inadequate supply of necessary nutrients and other requirements to a host organism

Question 17

What is virulence?

Answer 17

The degree to which a pathogen can cause disease.

Question 18

What is the incubation period?

Answer 18

The symptoms of a disease do not appear immediately on infection with a pathogen and the time between infection with the pathogen and the onset of symptoms is known as the incubation period.

Question 19

What is the difference between an epidemic or pandemic?

Answer 19

An epidemic refers to the contagious infectious or viral illness that spreads to many people in one specific geographic region, occurs in excess of the number of cases that would usually be expected of the infection or illness.

A pandemic refers to a contagious, infectious or viral illness that spreads but is not limited to one specific geographic region, and has the potential to include millions of people in many areas and countries across the globe.

Question 20

What are the two non cellular pathogens?

Answer 20

Prions and viruses

Question 21

What are prions?

Answer 21

Infectious particles made of protein and lacking nucleic acids.
They do not contain any genetic material and consist of a protein called PrP (prion protein)

Question 22

What are the two forms of prions?

Answer 22

PrPc is found naturally in nerve cells and plays a role in memory, learning and transmission of signals between cells.

PrPsc is the disease causing form and usually enters the body in infected meat, causing the nervous system to degenerate.

Question 23

How do prions ‘reproduce’?

Answer 23

• The normal PrPc protein can be transformed to the harmful disease causing PrPsc prion by contact with the harmful prion.
• Thus contact caused the PrPc protein to unfold and then resold abnormally so that its secondary structure is converted to that of the harmful PrPsc prion.
• As each new harmful prion is formed, it too can convert other normal protein into harmful prions.
• This process is not true biological reproduction

Question 24

What is the definition of a virus?

Answer 24

Non-cellular pathogens that attack all types of organisms, consisting of genetic material, either DNA or RNA, that can replicate only within a host cell — they are obligate intracellular parasites.

Question 25

Are viruses host specific?

Answer 25

Yes, a particular virus will cause a disease in only one kind or organism as they recognise specific surface molecules on the cell membrane of a specific host.

Question 26

What is the structure of a virus?

Answer 26

Viruses consist of DNA or RNA (not both) surrounded by a protein coat (capsid). This is referred to as a capsid and these viruses are said to be naked.

In some viruses the nucleocapsid is enclosed by an envelop. The outer envelop may have spikes of glycoproteins for recognition and attachment to their specific host cell.

Question 27

How do viruses reproduce?

Answer 27

A virus can be replicated only within a specific host cell. Host cells have receptor sites to which only specific viruses can bind. A host cell infected by a virus becomes a factory for the production of multiple copies of the virus. The mode of release of viral particles from an infected cell may be by budding or lysis.

Question 28

What is budding?

Answer 28

Enveloped viruses are released from an infected cell by a process of budding, in which virions are released until the infected cell finally dies.

Question 29

What is lysis?

Answer 29

Naked virus particles are commonly released from the host cell in a process called lysis. The infected host cell exploded as its plasma membrane disintegrates and viral particles are released into the extracellular fluid from where they can infect other cells.