Week 11 - Artificial Immune Systems

Question 1

What is an AIS (Artificial Immune System)?

Answer 1

Using the natural immune system as a metaphor for solving computational problems (not modelling the actual immune system, which is too difficult)

Question 2

Name some applications of AIS.

Answer 2

Fault detection, computer security, novelty detection, robot behaviour, machine learning

Question 3

What are the two non-specific lines of defence in the human immune system?

Answer 3

Barriers and general attack

Question 4

What are the two specific (adapted/targeted) defences in the human immune system?

Answer 4

Primary immune response (launches a response to invading pathogens)

Secondary immune response (remembers past encounters, leading to faster response the second time around)

Question 5

What is a pathogen?

Answer 5

Any agent (bacterium, virus etc) that can cause problems

Question 6

What are nonspecific defences?

Answer 6

The body’s first line against disease. They are not directed against a particular pathogen. They guard against all infections, regardless of cause

Question 7

What are specific defences?

Answer 7

Attempts by the body to defend itself against particular pathogens

Question 8

What is the body’s most important nonspecific defence and why?

Answer 8

The skin as it provides a continuous layer that protects almost the whole body, very few pathogens can penetrate the layers of dead cells at the skin’s surface, and oil and sweat glands at the surface of the skin produce a salty and acidic environment that kills many bacteria and other microorganisms. It acts as a barrier

Question 9

Name some non-specific defences other than the skin. How do they work?

Answer 9

Mucous membranes (tissues that protect the interior surfaces of the body that may be exposed to pathogens, serving as a barrier and secreting mucus, a sticky fluid that traps pathogens)

Mucus, cilia and hairs in the nose and throat (trap viruses and bacteria)

Stomach acid (destroys pathogens alongside enzymes)

Body secretions (such as mucus, saliva, sweat and tears - contain lysozyme, an enzyme that breaks down the cell wall of many bacterium)

Question 10

The body’s second line of defence is the inflammatory response. How does this work?

Answer 10

Triggered by injury to tissues in the body

The injured cells release a protein called histamine, which starts a series of changes called the inflammatory response

Blood flow is increased to the area

Capillaries leak, releasing phagocytes and clotting factors into the wound

Phagocytes engulf bacteria, dead cells, and cellular debris

Platelets move out of the capillary to seal the wounded area

Question 11

What is the most common phagocyte and what are some properties of it?

Answer 11

Neutrophil - 50-70% of the white blood cells in the body

Small so can move between cells

Engulfs pathogens

Question 12

Name another phagocyte other than neutrophil. What are some of its properties?

Answer 12

Macrophage

Consumes and destroys any pathogens it encounters

Rids the body of worn out cells and cellular debris

Question 13

What does a natural killer cell do?

Answer 13

Punctures the cell membrane of its target cell, allowing water to run into the cell so it bursts

This is effective in killing cancer cells and cells infected with viruses as it attacks cells infected with pathogens, not the pathogens themselves

Question 14

What is an antigen?

Answer 14

A substance that triggers the specific defences of the immune system - a substance that a macrophage identifies as not belonging to the body

Question 15

What are the main organs in the immune response and what do they do?

Answer 15

Bone marrow - manufactures the billions of white blood cells (WBC) needed by the body every day. Some newly produced WBC remain in the bone marrow to mature and specialise, whereas others travel to the thymus to mature

Lymph nodes - filter pathogens from the lymph and expose them to white blood cells

Spleen - filters pathogens from the blood. Stocked with WBC that respond to the trapped pathogens

Question 16

What is a lymphocyte?

Answer 16

A white blood cell that activate the immune reponse

Question 17

What are the two main types of lymphocytes?

Answer 17

B Cells and T Cells

Question 18

What do B-Lymphocytes (B Cells) do?

Answer 18

Produced and matured in the bone marrow, they are responsible for producing antibodies

Question 19

What are antibodies?

Answer 19

Special proteins that can bind to the antigen on the surface of a pathogen and help destroy it

Question 20

What do T-Lymphocytes (T Cells) do?

Answer 20

Matured in the thymus and have a variety of roles:
1. Cytotoxic T-Cells directly kill invaders
2. Helper T-Cells help other B and T cells do their job (e.g. they can “scan” body cells for signs of infection and increase B-Cell response if they find some)
3. Suppressor T-Cells suppress the activity of other B and T cells so that they don’t overreact

Question 21

What is the primary part of the adaptive immune response?

Answer 21

B and T cells develop the capability to generate antibodies to destroy or disable the pathogen (takes 3-7 days)

Cells also go through somatic hypermutation to ensure coverage of similar (not just identical) antigens

Question 22

What is the secondary part of the immune response?

Answer 22

Happens on encountering a similar antigen again

Occurs much faster because some B-cells from the primary response remain

These cells “remember” how to make the antibodies to destroy the pathogen

Question 23

Name 5 important properties of the immune system.

Answer 23

1. Recognition - can determine harmful from non-harmful and self from non-self
2. Distributed and self regulating - no central control
3. Diversity - almost infinite possible antibodies
4. Learning and memory - “remembers” old encounters with antigens
5. Metadynamics - non-used cells discarded, new cells created continuously

Question 24

What are three uses for AIS?

Answer 24

Machine learning, data mining, cyber security

Question 25

When were AIS’s first proposed and who by?

Answer 25

1995 by Cooke and Hunt

Question 26

What did Watkins and Timmis propose in 2004 and what does it do?

Answer 26

Artificial Immune Recognition Systems (AIRS) - uses immune system metaphors to classify examples in a training dataset

Question 27

What properties does an immune system approach to computer security need to include?

Answer 27

Distributed nature (lymphocytes find evidence of infection locally)

Diversity (keeping systems diverse means less likely to spread a virus/be vulnerable to attack)

Adaptability (new viruses/methods of attack should be recognised in the system)

Anomaly detection (difficult topic in computing)

Numbers (human immune systems must react quickly to large numbers of pathogens, AIS must deal with denial of service attacks)

Question 28

What three principles does Forrest et al’s 1994 matching algorithm solution to self/non-self distinction involve?

Answer 28

1. Each machine/copy of software has a unique copy of the protection algorithm (if you have one copy, if it is compromised, every computer will be vulnerable)
2. Detection is probabilistic (to make each piece of software different, use probabilistic of stochastic approach)
3. A robust system should look for any foreign activity not known signatures (traditional virus detection software is only as good as its recent update - a robust system should be able to think outside the box)

Question 29

How does Forrest et al’s 1994 matching algorithm solution to self/non-self distinction work?

Answer 29

Set of “self” strings generated from an alphabet

Set of “detectors” to protect the “self” strings

Each detector created by generating a random substring from one of the “self” strings, censored to ensure it is not also a “self” string

Matching occurs as a continual process - matching protected strings against detector collection (matching is not absolute)

If a detector matches a string, it has changed and an anomaly is detected