What is Immunity?

Immunity and Disease ■ Immunity is the ability of organisms to defend themselves against pathogens and toxins. ■ Infection is the harmful colonisation of an organism by another species.

Pathogens ■ A pathogen is an organisms that causes disease. ■ Many pathogens are microbes ■ Pathogens infect and cause harm

( Natural )

General Defence System Non-specific Defence: measures to prevent entry of all pathogens

Skin ■ Physical barrier of dead cells (epidermis) ■ Antimicrobial substances in sebum ■ Acidic nature of sebum and sweat ■ Blood clotting ■ Sebum moisturises which prevents cracking of skin (would allow entry).

Digestive system ■ Antimicrobial in saliva ■ HCl in stomach kills bacteria ■ Symbiotic bacteria in colon protect against pathogenic bacteria

Breathing System ■ Hairs and mucus in nasal passage ■ Mucus in bronchi contains antimicrobial ■ Cilia move mucus containing trapped foreign bodies up and out of respiratory tract.

Phagocytic White Blood Cells ■ Phagocytes are special defence cells that feed like amoeba ■ They engulf and digest material (e.g. a virus or bacterium) – phagocytosis ■ Macrophages are large aggressive phagocytes. ■ There are many phagocytes present in the lymph nodes.

Fever ■ Raised temperature following infection ■ Increases ability to defeat pathogens Interferon ■ Produced by virus-infected cells ■ Increases resistance of neighbouring non-infected cells

Specific Defence System How our body can tell the difference between self and non-self

Antibodies and Antigens ■ Antigens are non-self chemicals that stimulate the production of antibodies ■ Antibodies are specific proteins formed in response to the presence of an antigen – antibody binds specifically to the antigen

How an antibody operates/works? Deactivation of a bacterium by an antibody.

Monocytes ■ Make up 75% of the white blood cells ■ Some leave the blood and enter tissue becoming macrophages – a type of phagocyte ■ Once they have engulfed antigen, they “present” the antigen on their surface ■ Lymphocytes monitor monocytes for any signs of foreign antigens. ■ Monocyte action is accelerated by Helper T-cells

Phagocytosis Engulfing germ Germ Monocyte Germ

Lymphocytes ■ Specialised white blood cells ■ Able to distinguish between self and non self ■ Produced in the bone marrow ■ Huge numbers in lymphoid tissue –spleen, tonsils, adenoids, thymus, intestinal wall

LYMPHATIC SYSTEM

Lymphatic Vessels One-Way Valves

Tonsils

Thymus

Spleen

Immunity

Active Induced Immunity ■ Lymphocytes are activated by antigens on the surface of pathogens ■ Antibodies are produced by the lymphocytes Natural active immunity - acquired due to infection Artificial active immunity – vaccination ■ Takes time for enough B and T cells to be produced to mount an effective response.

Passive Induced Immunity ■ B and T cells are not activated and plasma cells have not produced antibodies. ■ The antigen doesn’t have to be encountered for the body to make the antibodies. ■ Antibodies appear immediately in blood but protection is only temporary.

Artifical Passive Immunity Artificial passive immunity ■ Used when a very rapid immune response is needed e.g. after infection with tetanus. ■ Human antibodies are injected. In the case of tetanus these are antitoxin antibodies. ■ Antibodies come from blood donors who have recently had the tetanus vaccination. ■ Only provides short term protection as abs destroyed by phagocytes in spleen and liver.

Natural Passive Immunity Natural Passive immunity ■ A mother’s antibodies pass across the placenta to the foetus and remain for several months. ■ Colostrum (the first breast milk) contains lots of IgA which remain on surface of the baby’s gut wall and pass into blood

Vaccination ■ A vaccine is a preparation which gives artificial active immunity to a pathogen ■ May contain live or dead inactivated pathogen or part of the pathogen. ■ This provides a harmless first encounter with the antigens of the potential pathogen

Benefits of Vaccination ■ Provides immunity without suffering the symptoms of the disease ■ Gives long-term protection ■ No long-term drug-taking required.

Examples of vaccines: MMR (Measles, mumps and rubella) 3 in 1 (whooping cough, diptheria and tetanus BCG (tuberculosis)

HIGHER LEVEL

B-lymophocytes ■ Produced and mature in the red bone- marrow of the foetus ■ Migrate to the lymphoid tissue ■ If stimulated by antigen, a B- lymphocyte cell multiplies and differentiates into huge numbers of: Plasma cells – producing antibodies Memory B cells – remain after infection

➢ B lymphocytes attack antigens in the blood or body fluids, by producing antibodies that surround the target. ➢ B lymphocytes move to the lymph nodes, where they acquire their receptor molecules. B LYMPHOCYTES:

➢ Each B cell produces just one type of antibody. ➢ The plasma cells produce antibody molecules, that bind to pathogens and toxins that are circulating in tissues or body fluids, and mark them for destruction by monocytes. ➢ When a B cell encounters matching antigen, they divide into plasma and memory cells.

Memory B-cells ■ Give immediate protection against future infections by the same pathogen or antigen ■ If they later detect a previous invader they rapidly reproduce ■ This produces a large population of antibody-secreting plasma cells

➢ Memory B and T cells that form during the first response to an antigen, do not engage in that first battle. ➢ They circulate in the body for years, and can intercept antigens far quicker. ➢ This is how we achieve immunity against many diseases – either by getting the disease once or by preventing them using vaccines. Long-term immunity

T-lymphocytes ■ Also known as T-cells ■ Also produced in the foetal bone marrow, but mature in the thymus ■ Migrate to the lymphoid tissue ■ Ignore free antigen - act against virus- infected cells and cancerous cells ■ Multiply and differentiate rapidly when antigen binds to them

Helper T-cells ■ Secrete chemicals which turn the specific defence system “on” and “off” ■ The Helper T-cells –stimulate the production of B-cells –stimulate the formation of Killer T-cells –accelerate the action of phagocytes

Killer T-cells ■ Destroy –virus-infected cells –tumour cells –organ-transplant cells (“non-self”) ■ Secrete perforin (punches holes) ■ Can stimulate target cell into apoptosis (programmed cell death or “cell suicide”)

Destruction of Cancer Cell by a Killer T-Cell

Suppressor T-cells ■ Maintain level of immune response ■ Inhibit –B cells –T cells –Monocytes ■ Suppressor T’s stop the immune response when the infection has been defeated

Memory T-Cells Like memory B-cells they survive a long time and can respond to a specific invader in the future Memory T-cells stimulate memory B- cells to start producing antibodies and they stimulate killer T-cells

Summary of T-cells T-cells do not produce antibodies instead they act in one of four processes: 1.Helper T cells which recognise antigens, enlarge, and secrete chemicals, such as interferon, which stimulate the production of B cells. 1.Killer T cells which attack cells containing a foreign antigen, secrete a chemical called perforin that perforates the membranes of cells 1.Suppressor T cells which stop immune responses 1.Memory T cells which can memorise the immunity, even for life.

Summary of Lymphocytes

Lymphocyte interactions ■ B cell surface antibodies bind antigen ■ Helper T cells also bind, releasing interleukins ■ These chemicals stimulate B cells to multiply and differentiate ■ T cells encountering monocytes that are presenting antigen are stimulated to multiply and differentiate

Human Immunodeficiency Virus