Cellular response

Immunity is the ability of the body to resist infection by a foreign body or to overcome the infection, immunity can be either innate or acquired.

Innate immunity is immunity that you are born with, this takes form of skin, stomach acids, lysozyme and phagocytosis

Acquired immunity is slightly different, this is when the presence of an antigen (which is recognised by bodily
cells as foreign), causes the production of antibodies.
Antibodies (left) are 'Y' shaped with two receptor or binding sites which are specific to certain antigens. Our body's contain thousands of separate cells that are able to produce the antibodies to antigens.

If immunity is naturally acquired then T-cells and B-cells are produced.

If the B-cells sense the presence of a foreign antigen then the multiply rapidly. Some of them will become memory cells where others will mass produce the appropriate antibody. This is called a humoral response.

When a human beco
mes infected by a micro-organism, the foreign proteins that are present in the host cell move to the surface of the cell and act as antigens. These are then picked up by a specific T-cell called the killer T cell. The killer T cells destroy the infected cell by perforating the membrane with a special chemical. This is called a cell-mediated response

As you may or may not know there is a second type of T-cell, this is called the helper T cell, it acts as a sniffer dog, patrolling the body, looking for foreign antigens and activating B-cells and killer T cells. In the video below we can see a killer T cell 
attacking a cancerous cell.

When it comes to fighting of diseases, the body is said to have two responses. One is calles the primary response and the other is called the secondary response. The primary response occurs on the first time when the pathogen is first discovered, this is usually slow and does not stop the person suffering from the disease. The secondary response on the other hand is much quicker and much more effective when fighting off diseases. During the primary response memory cells are produced, these remain in the body which allows the person's secondary response to be so fast, this person would have gained natural immunity.

Immunity can also be artificially acquired, this is done through inoculations. A vaccination is a form of inoculation, this may be the introduction of a harmless form of the pathogen (cowpox/smallpox) it could be a weakened version of the pathogen (polio) or it could well be a dead microbe such as the cholera vaccine. In all three of these cases memory cells and antibodies are produced and the person becomes artificially immune.

As well as artificial and natural immunity there is also active and passive:
  • Active is when you produce your own antibodies.
  • Passive is when you receive ready-made antibodies (through colostrum etc.) It must be noted that Passive immunity may only last a short time as no memory cells are formed.

An allergic reaction is simple, all it is, is an over reaction to a harmless substance. This may be pollen or dust, in reality these do the body no harm, yet the reactions can be fatal, due to the nature of hypersensitivity

We have talked a lot about foreign bodies, but what does this mean? 
Foreign bodies are cells that are recognised as non-self due to their antigenic markers.

The Human blood group system works as an ABO system, there are four different groups:
  • A
  • B
  • AB
  • O
People with blood group A have A-antigens, people with B have B-antigens, people with AB have both A and B antigens and people with O have neither.

If you have blood group B you have anti-A antibodies and vise versa, AB have neither and O have both.

If someone with a blood group A was to get a B transfusion then their blood would agglutinate, this is the clumping of blood due to the antibodies holding the together. A similar problem occurs with organ transplants, this is because the bodies T cells recognise it as non self and attack it, which can be fatal. Therefore immunosuppressor drugs must be used to stop this from happening, although theses have their problems to, as they stop the immune system from functioning, leaving the person succeptible to disease.

Autoimmunity, this is when the body attacks its own cells, due to it not being able to recognise 'self cells'. This is what happens during multiple sclerosis.