Immunity – ability of the body to resist infection, or overcome an invading organism.

Immunity can be innate or acquired.

Innate immunity – inborn, unchanging, and non-specific.

Skin acts as a barrier.

Stomach acid kills pathogens.

Lysozyme in tears.

Also – interferon helps prevent multiplication of viruses, and phagocytosis.

Phagocytosis

• ‘cell – eating’

• foreign bodies are engulfed and destroyed

• phagocytic cells: monocytes and macrophages

• macrophages in connective tissue throughout body

• macrophages have many lysosomes with digestive enzymes

1.Macrophage detects bacterium and moves towards it.

2. Phagocytes engulfs bacterium in a vacuole by infolding of membrane.

3. Lysosomes fuse with vacuole.

4. Lysosomes release enzymes which digest bacterium.

5. Bacterium products absorbed by phagocyte.

*fig. 7.2 p.52*

• during infection, many phagocytes engulf many bacteria

• dead bacteria and phagocytes accumulate at injury site forming pus

• large number of immobile macrophages line liver, spleen and lymph nodes to remove foreign bodies from passing blood or lymph.

Acquired Immunity• natural or artificial

• it is gained by immune system producing antibodies in response to foreign antigens

Antigen – molecule recognised as foreign to body

• antigen markers on body cells known by immune system as ‘self’ antigens

• carried out by B and T-lymphocytes (white blood cells)

Naturally Acquired Immunity

B-cells • made in bone marrow, and pass to lymph nodes

• produce antibodies in response to foreign antigens

Receptor sites on antibodies specific to particular antigen.

• helper T-cells patrol body and activate B and T-cells when foreign antigen present.

• B-cells multiply rapidly

• some produce antibodies, some become memory cells

• receptor sites on antibodies join with foreign antigen rendering harmless

*see fig. 7.5 p.54*

• humoral response

T-cells (made in bone marrow, pass to thymus)

• when cell becomes infected by pathogen, pathogen’s antigens become present on cell membrane

• helper T-cells activate killer T-cells

• killer T-cells have specific receptors which join with foreign antigens

• killer T-cells release digestive enzymes to destroy infected cell.

*see fig. 7.4 p.53*

• cell-mediated response

• made in bone marrow, pass to thymus

Primary Response• person is infected by pathogen for first time

• latent period exists between antigen entering body, and antibodies being produced.

• memory B and T-cells produced

Secondary Response• on next exposure to antigen, memory cells are quickly stimulated to produce clones

•antibody production is faster, higher concentration, response lasts longer, often prevents disease. * Fig. 7.5 p.55*

Artificially Acquired Immunity• body is injected with harmless dose of foreign antigen

• induces Band T-cell production, and antibody formation

• also causes production of memory cells.

Vaccines• antigen can be harmless form (smallpox/cowpox), weakened (polio), dead (cholera), or chemically treated (attenuated) (tetanus).

Active (Acquired) Immunity• protection gained by person making antibodies

• natural or artificial

Passive Immunity• protection gained by person being given antibodies

• effects are short-lived

• natural or artificial

For each situation, say whether the immunity gained is passive/active, and natural/artificial.1.Person catching cold

2.Person given an injection of tetanus antibodies

3.Breastfeeding

4.A polio vaccine

Natural active

Artificial passive

Natural passive

Artificial active

Allergies

Allergic reaction – over-reaction of immune system to a harmless substance

• immune system produces antibodies, which connect with mast cells in connective tissue

• mast cells secrete histamine

• histamine causes runny nose, cough etc.

• relived by antihistamine drugs

* Fig. 7.6 p.57*

• all cells have antigen signature, any different antigens attacked by immune system

• transplanted tissues must be as close as possible or are rejected by immune system

Autoimmunity – immune system attacks own body cells, e.g.

1. Rheumatoid arthritis – cartilage in joints attacked

2. Multiple Sclerosis (MS) – myelin sheath around nerves attacked

ABO Blood Groups

*Copy/Refer Fig. 7.7 p.58*

• certain blood groups are non-compatible

• if wrong blood groups are mixed, antibodies in person’s own blood attacks foreign cells

• red blood cells clump together => agglutination

*Fig. 7.8 p.58*