Immunity

Question 1

Describe the importance of non-specific immunity to include natural barriers and inflammation

Answer 1

Non specific defence mechanisms: these protect against any a wide range of dangers, usually present from birth and sometimes termed as ‘innate’

1. Epithelial barriers:
   • Consists of skin and mucous membranes
   • Healthy, intact skin is a barrier against pathogens
   • Nose hair: filter system to stop foreign bodies entering our respiratory tract.
   • Cilia: moves mucus and inhaled foreign materials towards the throat, so it is coughed up or swallowed.
2. Epithelial secretions:
   • Anti-bacterial, and often acidic containing antibodies and enzymes
   • Sebum and sweat contain antibacterial and antifungal properties
   • The one-way flow of urine from the bladder minimises the risk of infection ascending through the urethra into the bladder
3. Anti-microbial substances:
   • Saliva - : washes way food debris to prevent bacterial growth. Contains antibodies, lysozyme and buffers to neutralise bacterial acids that promote dental decay.
   • Lysozyme: an anti-bacterial enzyme present in tears (lacrimal apparatus):
   • Hydrochloric acid: present in gastric juice
   • Antibodies: protective proteins inactivate bacteria and are found coating membranes exposed to the external environment, e.g. genitourinary, respiratory and gastrointestinal tracts
   • Interferons: chemicals are produced by T-lymphocytes, macrophages and body cells that have been invaded by viruses. They activate immune cells, including killer T-cells, prevent viral replication within infected cells, and reduce the spread of viruses to healthy cells.
4. Phagocytosis: (cell eating)
   • Neutrophils and macrophages are examples of phagocytic cells.
   • Phagocytes migrate to sites of inflammation and infection as they are attracted to chemicals that are released by invading microbes.
   • Phagocytes attack, digest, and destroy foreign cells, damaged cells and debris.
   • They may also release a chemical which is toxic to the invading microbes into the interstitial fluid.
   • The chemicals released alert the immune system to the presence of a threat.
   • Neutrophils are short-lived as they destroy themselves with their toxic chemicals too.
   • Macrophages live longer, and link the non-specific defences with specific immunity
5. Inflammatory response (physiological response to tissue damage):
   • Purpose: to isolate, inactivate and remove both the causative agent and damaged tissue, so that healing can take place.
   • Signs of inflammation: redness, heat, swelling, pain. Conditions with an ‘-itis’
   • What triggers the inflammatory response?Extremes of temperature, pH, trauma, foreign bodies etc.
   • What happens? Increased blood flow, accumulation of tissue fluid, migration of leukocytes, increased core temperature, pain and suppuration (pus forming).
   • Substances released: histamine (from mast cells and basophils), serotonin (from platelets, mast cells and basophils), prostaglandins (most cells), heparin (liver, mast cells), bradykinin (tissues and blood).
   • Increased blood flow: arterioles dilate, capillaries expand. Provides more oxygen and nutrients to the area. Responsible for the increased temperature, swelling and redness. Caused by local release of histamine and serotonin.
   • Accumulation of tissue fluid: fluid leaves blood vessels and moves into interstitial space. Caused by increased blood flow, and histamine, serotonin and prostaglandins making capillary walls more permeable.
   • Migration of leukocytes: Loss of fluid from the blood thickens it, slowing flow and allowing the normally fast-flowing white blood cells to make contact with, and adhere to, the vessel wall. Neutrophils adhere to the blood vessel lining and enters the tissues for phagocytosis. Macrophages begin phagocytosis after 24 hours.
   • Increased core temperature: inhibiting the growth and division of microbes while promoting the activity of phagocytes
   • Pain: encourages protection. local swelling compresses sensory nerve endings.
   • Suppuration: collection of material - dead phagocytes, dead cells, fibrin, inflammatory exudate, and living and dead microbes
6. Natural killer (NK) cells:
   • a type of non-selective lymphocyte
   • They patrol the body, searching for abnormal host cells.
   • Cells that have been infected with a virus, or mutated cells that might become malignant, frequently display unusual markers on their cell membranes, which are recognised by NK cells.
   • Having detected an abnormal cell, the NK cell immediately kills it.

Question 2

Describe the importance of specific immunity

Answer 2

Specific immunity is:
• mechanisms directed against one specific invader
• the body ‘learns’ and ‘remembers’ the specific antigens, building a immunological memory
• Sometimes termed as adaptive

Question 3

Explain the terms antigen and antibody

Answer 3

• Antibody: defensive protein synthesises by B-lymphocytes in response to the presence of antigen
• Antigen: protein that stimulates the body’s immunological defences

Question 4

Briefly describe humoral immunity to include the role of B and T lymphocytes

Answer 4

1. Unlike T-cells, B-cells recognise and bind antigen particles directly, without having to be presented with them by an antigen-presenting cell.
2. B-cells make antibodies.
3. Some of these antibodies are released into the bloodstream for distribution around the body but each B-cell also displays the antibody that it makes on its cell membrane. These bound antibodies act as antigen receptors.
4. Helper T cells then enable the B cell to enlarge and proliferating, making 2 distinct types of B cell: memory B cells and plasma cells.
5. Memory B cells: provide long term immunity for that antigen
6. Plasma cells: produce antibodies that bind to, and destroy the antigen

Question 5

Briefly describe cell-mediated immunity to include the role of T lymphocytes

Answer 5

• When T cells encounter their antigen for the first time, they become sensitised to it.
• T-cells cannot detect free antigen in body fluids.
• To recognise and be activated by antigen, the T-cell must be ‘presented’ with it on the membrane of another cell.
• These cells are called antigen-presenting cells (APCs).
• Many different cell types present antigen to T-cells, and so are important in activating the adaptive immune system when antigen is present.

Types of T cells:
1. Cytotoxic (CD8): inactivate anything carrying antigens by releasing powerful toxins. Main function is to destroy abnormal body cells which are infected or cancerous.
2. Helper (CD4): Most common of T cells. Essential for cell mediated and antibody mediated immunity. Produce cytokines (interleukins and interferons) to support and promote CD8 cells and macrophages. Stimulate B cells to produce antibodies.
3. Regulatory: These cells act as ‘brakes’, turning off activated T- and B-cells. This limits the powerful and potentially damaging effects of the immune response. Regulatory T-cells are involved in immunological tolerance; they help prevent the development of autoimmunity and protect the fetus in pregnancy.
4. Memory: Respond rapidly to subsequent encounters with the same antigen.

Question 6

Outline the physiological process of immunity in the context of active and passive immunity

Answer 6

• the immune response to an antigen following the first exposure is called the primary response.
There is a slow and delayed rise in antibody levels, peaking 1–2 weeks after infection. The antibody produced is mainly IgM. This delayed response reflects the time required to activate the T-cell system, which then stimulates B-cell division.
Antibody levels start to fall once the infection is cleared, but if the immune system has responded well, it will have generated a population of long-lived memory B-cells, making the individual immune to future infection.
• Second and subsequent exposures give rise to a secondary response.
The immune response is much faster and 10–15 times more powerful because the memory B-cells generated after the first infection rapidly divide and antibody production begins almost immediately. Antibody produced is mainly IgG, which is more effective than IgM. (Waugh 2018)

• Active: the individual has responded to an antigen and produced their own antibodies, lymphocytes are activated and the memory cells formed provide long-lasting resistance.
• Passive: the individual is given antibodies produced by someone else. The antibodies break down with time, so passive immunity is relatively brief.
• Natural: The body may be stimulated to produce its own antibodies by either having the disease or having a subclinical infection (active). Acquired before birth by the passage of maternal antibodies across the placenta to the fetus, and to the baby in breast milk (passive).
• Artificial: In response to the administration of dead or live artificially weakened pathogens (vaccines) or deactivated toxins (toxoids) (active). Ready-made antibodies, in human or animal serum, are injected into the recipient (passive).

Question 7

Outline the role of the lymphatic system in immunity

Answer 7

Lymphatic system:
• Lymphatic system maintains the fluid balance by retiring tissue fluid into the venous blood stream
• The lymphatic system contains lymphoid structures which contain lymphocytes. Lymphoid structures include the tonsils, thymus, spleen, and bone marrow.
• Lymph nodes filter lymphatic fluid (AKA lymph) as it passes through them.
• Organic material is destroyed in the lymph nodes by antibodies and macrophages via phagocytosis.
• Fluid may pass through several nodes before being filtered, cleared of foreign material and debris before being returned to the circulatory system.
• Activated T and B cells multiply in lymph nodes

Question 8

Identify the tissues and organs of the lymphatic system

Question 9

Describe the role of anti-d immunoglobulin in childbirth

Question 10

List the vaccinations given to the neonate and identify when childhood vaccinations are given