Non-specific Immune Response

When someone is infected by a disease-causing organism, several mechanisms in their body act to destroy the invading pathogen. This task is performed by the immune system and is known as the immune response. [blank_start]Non-specific[blank_end] responses help to destroy any invading pathogen, whereas [blank_start]specific[blank_end] immunity is always directed at a specific pathogen.

A stream of tears helps to wash out foreign materials and attacks any [blank_start]bacteria[blank_end] on the surface of the eye. Tears contain an enzyme called [blank_start]lysosyme[blank_end] that kills bacteria by breaking down their [blank_start]cell walls[blank_end]. The same enzyme is found in saliva and nasal secretions, protecting the body from harmful bacteria in the air we breathe or the food we eat.

An injury, cut or graze enables [blank_start]microbes[blank_end] and other foreign material to enter the body. A [blank_start]blood clot[blank_end] will rapidly seal the wound. But inflammation at the site, known as the inflammatory [blank_start]response[blank_end], helps to destroy invading microbes. Damaged white blood cells and [blank_start]mast cells[blank_end], found in the connective tissue below the skin and around blood vessels, release special chemicals, such as [blank_start]histamine[blank_end]. These chemicals cause the arterioles in the area to [blank_start]dilute[blank_end], increasing blood [blank_start]flow[blank_end] in the capillaries at the infected site. Histamines also increase the permeability of the [blank_start]capillaries[blank_end]: cells in the capillary walls [blank_start]separate[blank_end] slightly, so the vessels leak. Plasma fluid, white blood cells and antibodies leak from the blood into the tissue causing oedema ([blank_start]swelling[blank_end]). The infecting microbes can now be attacked by these intact white blood cells.

What are phagocytes?

Only macrophages are phagocytes

Two types occur: B and T cells. Involved in the immune response including antibody production and immunity. Some cells only last a few days; others can survive for years.

Circulate in the blood for a day or 2 before they move into the tissue by squeezing between the cells of capillary walls. Here they become macrophages and engulf bacteria, foreign matter and cell debris. Numerous in the lungs, liver, kidneys, spleen and lymph nodes.

Leave blood capillaries by squeezing between the cells of capillary walls. Ingest and destroy bacteria. 80 million produced every minute (more during infection). Last only a few days.

Produce the chemical histamine involved in the inflammatory response

Red blood cells contain a nucleus

White blood cells contain a nucleus

Action at the infected site: Chemicals released by [blank_start]bacteria[blank_end] and the cells damaged at the site of infection attract phagocytic white cells. [blank_start]Neutrophils[blank_end] are the first to arrive; they engulf between 5 and 20 bacteria before they become [blank_start]inactive[blank_end] and die. The neutrophils are then followed by [blank_start]macrophages[blank_end]. These larger, longer-lived cells can each destroy around 100 bacteria. They will also ingest debris from damaged cells, and foreign matter such as particles of [blank_start]carbon[blank_end] and dust in the lungs. The ingested material is enclosed within a [blank_start]vacuole[blank_end]. [blank_start]Lysosomes[blank_end] containing digestive enzymes fuse with the vacuole, the enzymes are released, and they destroy the bacteria or other foreign material. The large numbers of phagocytic cells that collect at the site of infection can engulf huge numbers of bacteria. After a few days the area is full of dead cells, mainly neutrophils, which form a thick fluid called [blank_start]pus[blank_end]. The pus may break through the surface of the skin, but usually it gradually gets broken down and absorbed into the surrounding tissue.

Action to prevent the spread of infection: In spite of intense [blank_start]phagocytic[blank_end] activity at the infected site, some live [blank_start]bacteria[blank_end] usually get carried away either by the blood or in the [blank_start]lymph[blank_end]. The spread of these bacteria is hindered by the action of [blank_start]macrophages[blank_end] in the lymph nodes, [blank_start]spleen[blank_end] and liver. Only occasionally does the system fail, leading to widespread infection known as [blank_start]septic shock[blank_end] or 'blood poisoning'.

Label the diagram:

Tissue fluid drains into the [blank_start]lymphatic[blank_end] vessels. The fluid, called lymph, flows along the lymph vessels. It passes through lymph nodes and eventually returns to the blood via the lymphatic and [blank_start]thoracic[blank_end] ducts. As lymph passes through the lymph nodes any pathogens present activate [blank_start]lymphocytes[blank_end] and macrophages, which can then destroy the microbes.

[blank_start]Interferon[blank_end] provides non-specific defence against [blank_start]viruses[blank_end], and some bacteria and protozoa. [blank_start]Microbe-infected[blank_end] cells produce this [blank_start]protein[blank_end]; it [blank_start]diffuses[blank_end] to the surrounding cells where it prevents microbes from multiplying. It inhibits microbial [blank_start]protein synthesis[blank_end] and in this way limits the formation of new microbe particles.