8 Immunity: defenceagainst disease

Immunity

• Infection is entry into the body of a micro-organism that may cause disease. Infection does not necessarily lead to disease.

• The immune system has two kinds of response to the entry of foreign material. One response involves natural or innate immunity, which is non-specific.

• The other response involves acquired or adaptive immunity, which is highly specific. Specific immunity involves the production of specialised cells and chemical substances known as antibodies which act against a particular infection.

Non-specific immunity

• The defence system of the body is called the immune system.

• The immune system is able to identify ‘non-self’ material from ‘self’.

• The immune system can produce two kinds of response to invading foreign material, namely non-specific and specific.

Non-specific immunity

• Micro-organisms are prevented from entering the body by a number of non-specialised features. This is the first line of defence.

• There is a second line of defence against foreign material that enters the body.

Specific immunity

• If non-specialised defences fail to prevent infection, specialised responses occur.

• All cells have protein markers on their surfaces.

• Non-self markers on cells entering a person are called antigens.

Specific immunity

• A number of different kinds of cell are involved in specific immunity.

• The phenotype is the physical, biochemical or physiological expression of the genotype.

• Some cells produce antibodies that circulate in body fluids and react with specific antigens.

Different kinds of antibodies

• The immune response produces different kinds of T cells.

• Different kinds of T cells have different functions.

• The immune system contains many lymphoid organs and tissues.

Acquiring specific immunity

Acquiring specific immunity

• Specific immunity can be acquired in different ways.

• In actively acquired immunity, the immune system of a person produces antibodies in response to antigens.

• In passively acquired immunity, a person receives antibodies from an outside source.

• Both active and passive immunity can be acquired naturally or artificially.

Adverse events associatedwith immunity

• Any part of the immune response can be faulty.

• Cells of the immune system are involved in allergic reactions.

• An immune system can lose the ability to distinguish ‘self’ from ‘non-self’.

Adverse events associatedwith immunity

• The action of the immune system can be reduced by treatment with certain drugs.

• Antibodies are sometimes injected to inhibit an immune response.

• Most plants resist infection by mechanical and chemical means