Defence and Immunity

Question 1

What are Lymphocytes and where are they found and made?

Answer 1

Lymphocytes are white blood cells that are also one of the body’s main types of immune cells. They are made in the bone marrow and found in the blood and lymph tissue.

Question 2

What are Macrophages?

Answer 2

Macrophages are specialised cells involved in the detection, phagocytosis and destruction of bacteria and other harmful organisms. In addition, they can also present antigens to T cells and initiate inflammation by releasing molecules (known as cytokines) that activate other cells.

Question 3

What is the first line of defence? (Examples and general overview)

Answer 3

The objectives of nonspecific mechanisms of defence are to prevent microorganisms from gaining a foothold in the body and to destroy them if they penetrate to the deeper tissues.
Examples include:
Mechanical barriers; ie the skin.

Mucous membranes of the urinary, respiratory and digestive tracts: They are moist and permeable, but their fluids, such as tears, mucus, and saliva, rid the membrane of irritants.

Chemical defences: ie enzymes in tears and saliva, thelactic acid in the vagina, hydrochloric acid of the stomach and spermine in semen.

Genetic barriers (Some humans are more resistant than others to diseases)

Inflammation: mobilizes components of the immune system, sets into motion repair mechanisms, and encourages phagocytes accumulate in the whitish mass of cells, bacteria, and debris called pus

Question 4

What is the second line of defence? (examples and general overview)

Answer 4

The second line of defence becomes active if pathogens make it past the first line of defence. The second line of defence is a group of cells, tissues and organs that work together to protect the body. This is the immune system.

The cells involved are white blood cells (leukocytes), which seek out and destroy disease-causing organisms or substances. The different types of white blood cells are: Neutrophils, T helper cells, Cytotoxic T cells, Macrophages, Dendric cells, B cells, Suppressor T cells.

The tissues and organs involved in the immune system are the lymphatic system, lymph nodes and lymph fluid.

Question 5

Specific vs non specific defences

Answer 5

Non specific (innate immunity) and specific (acquired immunity) are the two defence systems of the immune system. Nonspecific protective mechanisms repel all microorganisms equally, while specific immune responses are tailored to particular types of invaders. Both systems work together to thwart organisms from entering and proliferating within the body. These immune mechanisms also help eliminate abnormal cells of the body that can develop into cancer.

Nonspecific immunity examples: skin, chemical barriers, cells that attack foreign cells, and body cells harbouring infectious agents.

Specific (acquired) immunity examples: Lymphocytes (Specialised white blood cells)

Question 6

Five cardinal signs of inflammation

Answer 6

Redness
Heat
Swelling
Pain 
Impairment of function

Question 7

What is inflammation and what is its cause?

Answer 7

A process by which the body’s white blood cells and substances they produce protect us from infection with foreign organisms, such as bacteria and viruses. Symptoms include: Redness, Swollen joint, Joint pain, Joint stiffness, and loss of joint function

Question 8

Benefits of the inflammatory response

Answer 8

Prevents the spread of damaging agents to nearby tissues through swelling which isolates the foreign substances from further contact with body tissues.

Attracts white blood cells called phagocytes that “eat” germs and dead or damaged cells. This process is called phagocytosis. Phagocytes eventually die. Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes.

Extra heat and blood flow encourages healing.

Question 9

What causes pain in inflammation?

Answer 9

The protective process of inflammation (ie swelling, increased blood flow) may stimulate nerves and cause pain in that way.

Also the increased number of cells and inflammatory substances within the joint cause irritation, swelling of the joint lining and, eventually, wearing down of cartilage (cushions at the end of bones)

Question 10

Antigen

Answer 10

Any substance that causes the body to produce specific antibodies which can react with the antigen. Substances that invoke the immune response.

Antigens are usually foreign substances. The body’s own substances, recognised as “self”, do not normally act as antigens; can illicit a response to others, eg tissue transplants.

Question 11

Antibodies

Answer 11

Antibodies are large Y-shaped proteins. They are recruited by the immune system to identify and neutralise foreign objects like bacteria and viruses.

Each antibody has a unique target known as the antigen present on the invading organism. This antigen is like a key that helps the antibody in identifying the organism. This is because both the antibody and the antigen have similar structure at the tips of their “Y” structures.

Just like every lock has a single key, an antibody has a single antigen key. When the key is inserted into the lock, the antibody activates, tagging or neutralising its target. The production of antibodies is the main function of the humoral immune system.

Question 12

Cellular mediated immunity

Answer 12

The formation of specifically sensitised lymphocytes that have the capacity to attach to the foreign agents and destroy it

Particularly effective against fungi, parasites, intracellular viral infections, cancer cells, and foreign tissue transplants

Question 13

Immunological Surveillance

Answer 13

Cancer cells have surface components called tumour-specific antigens

These are recognised as “non self” by sensitised killer T or sensitised macrophages which then destroy them.

This immune response is called immunological surveillance.

Question 14

Primary and secondary response

Answer 14

After an initial contact with an antigen by the B-cells and T-cells there is a period of several days during which no antibody is present.
Then there is a slow rise in the antibody titre as proliferation of the cell populations occur, followed by a gradual decline
This response of the body to first contact is called the primary response.
During the primary response the body is primed or sensitised and there is proliferation of immunocompetent lymphocytes.

Question 15

Humoral immunity

Answer 15

The body produces circulating antibodies capable of attacking an invading agent

Particularly effective against bacterial and viral infections. Thymic hormone is active in humoral immunity

Cellular immunity and

Question 16

Repeated immune response to antigen

Answer 16

If the antigen is contacted again there is immediate proliferation of immunocompetent lymphocytes and the antibody titre is elevated.
This is the secondary response or the anamnestic response.
This response occurs because some of the immunocompetent lymphocytes remain as memory cells.
This provides the basis for immunisation against certain diseases.

Question 17

Active immunity:

Answer 17

Active immunity occurs when an individual is given an antigen that stimulates specific antibody production. Repeat doses elevate antibody concentration and result in long-lasting immunity against the disease.

There are two types of active immunity

Naturally acquired - requires contact with pathogen
Artificially acquired - vaccines

Question 18

Cell types associated with cell-mediated immunity

Answer 18

T lymphocytes - provide cellular/ cell-mediated immunity

Helper T cells (aka CD 4 cells) - help in the maturation of B cells into plasma cells and memory B cells. They also help activate cytotoxic T cells and macrophages.

Cytotoxic T cells (aka CD 8 cells) - directly attack and kill other cells

Memory T cells - immunological memory

Suppressor T cells - end the immune response.

Question 19

What is passive immunity?

Answer 19

Passive immunity occurs when a person is given antibodies to help combat disease or minimise infection. This form of protection is short lived.
There are two types of passive immunity:

Naturally acquired - mother-to-foetus/through breast milk
Artificially acquired - gamma globulin

Question 20

Immunodeficiencies

Answer 20

Insufficient or abnormal immune cells, phagocytes, or complement that are produced e.g. AIDS

Question 21

Autoimmune diseases

Answer 21

When the immune system attacks its own body parts

Question 22

Cell types associated with humoral immunity (antibody mediated)

Answer 22

B lymphocytes (B cells) 
Plasma Cells 
Produces antibodies (immunoglobulins)

Question 23

What is the difference between B lymphocytes and T lymphocytes?

Answer 23

The two categories of lymphocytes are B lymphocytes and T lymphocytes. These are commonly referred to as B cells and T cells. Both originate from stem cells in the bone marrow. From there, some cells travel to the thymus, where they become T cells. Others remain in the bone marrow, where they become B cells.
The job of B cells is to make antibodies, which are proteins produced by the immune system to fight foreign substances known as antigens.
Each B cell is set to make one specific antibody. Each antibody matches an antigen in the same way that a key matches a lock, and when this happens, the antigen is marked for destruction.

The job of T cells is to help the body kill cancer cells and control the immune response to foreign substances. They do this by destroying cells in the body that have been taken over by viruses or become cancerous.

Question 24

Neutrophils

Answer 24

These cells primarily attack bacteria. They rush to the site of incoming bacteria to fight them, but are easily killed. Neutrophils only last a few days in the body (before they self destruct), but our bone marrow produces more every day. Some bacteria avoid neutrophils by hiding inside cells.

Question 25

T helper cells

Answer 25

These cells are like the bosses. They give instructions to other cells by producing signals. Each T helper cell only looks out for one type of pathogen. Many T helper cells are needed to watch for many different diseases or invaders.

Question 26

Cytotoxic (killer) T cells

Answer 26

These are killer cells. They punch holes in the walls of the pathogen cell so that the contents ooze out

Question 27

Macrophages

Answer 27

These cells “eat” (ingest) or clean up the mess of dead cells

Question 28

Dendritic cells

Answer 28

These cells are like the spies. They notice if there is an invader and then present evidence of the invader to T cells in the lymph nodes.

Question 29

B cells

Answer 29

These produce antibodies, which lock onto the antigen of invading bacteria and immobilise them until the macrophage consumes them. Some B cells become memory cells after being activated by the presence of antigen. These cells are able to live for a long time and can respond quickly following a second exposure to the same antigen.

Question 30

Suppressor T cells

Answer 30

When the infection is gone, the immune system needs to be calmed down (or the killer cells may keep killing). The suppressor T cells slow down or turn off the immune system to prevent damage to good cells.

Question 31

Lymphatic System

Answer 31

The lymphatic system is a system of thin tubes that runs throughout the body. These tubes are called lymph vessels. They contain lymph.

Question 32

Lymph

Answer 32

Lymph is a fluid in which white blood (immune) cells are found

Question 33

Lymph nodes

Answer 33

Lymph nodes are small, round masses of tissue that are found in certain areas (such as the neck, groin and armpits). They filter bacteria and other foreign materials out of lymph and expose them to B and T cells and macrophages that can engulf them. These cells multiply in response to accumulation of such materials, which is why lymph nodes swell during infections.

Question 34

Acute Inflammation vascular effects on the body:

Answer 34

Blood vessels in the area constrict briefly before dilating (vasodilation). Vasodilation may last from 15 minutes to several hours.

Next, the walls of the blood vessels, which normally allow only water and salts to pass through easily, become more permeable. Protein-rich fluid, called exudate, is now able to exit into the tissues. Substances in the exudate include clotting factors, which help prevent the spread of infectious agents throughout the body. Other proteins include antibodies that help destroy invading microorganisms.

As fluid and other substances leak out of the blood vessels, blood flow becomes more sluggish and white blood cells begin to fall out of the axial stream in the centre of the vessel to flow nearer the vessel wall. The white blood cells then adhere to the blood vessel wall, the first step in their emigration into the extravascular space of the tissue.

Question 35

Acute Inflammation cellular effects on the body:

Answer 35

The most important feature of inflammation is the accumulation of white blood cells at the site of injury. Most of these cells are phagocytes, certain “cell-eating” leukocytes that ingest bacteria and other foreign particles and also clean up cellular debris caused by the injury. The main phagocytes involved in acute inflammation are the neutrophils, a type of white blood cell that contains granules of cell-destroying enzymes and proteins. When tissue damage is slight, an adequate supply of these cells can be obtained from those already circulating in the blood. But, when damage is extensive, stores of neutrophils—some in immature form—are released from the bone marrow, where they are generated.

To perform their tasks, not only must neutrophils exit through the blood vessel wall but they must actively move from the blood vessel toward the area of tissue damage. This movement is made possible by chemical substances that diffuse from the area of tissue damage and create a concentration gradient followed by the neutrophils. The substances that create the gradient are called chemotactic factors, and the one-way migration of cells along the gradient is called chemotaxis.

Large numbers of neutrophils reach the site of injury first, sometimes within an hour after injury or infection. After the neutrophils, often 24 to 28 hours after inflammation begins, there comes another group of white blood cells, the monocytes, which eventually mature into cell-eating macrophages. Macrophages usually become more prevalent at the site of injury only after days or weeks and are a cellular hallmark of chronic inflammation.

Question 36

T Cell-Mediated immunity

Answer 36

Cell-mediated immunity is an immune response that does not involve antibodies. Rather, cell mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to antigen.