The humoral response

The humoral response is one of the specific defence mechanisms used to protect the body from disease. It involves the production of specific antibodies to destroy pathogens.

The humoral response involves the use of B lymphocytes or B cells. B cells produce and are covered in proteins known as antibodies. It is called the humoral response as antibodies are found in body fluids, which are otherwise known as 'humors'.

The humoral response

The humoral response is so-called because it involves antibodies that are found in body fluids (or humors).

The stages of the humoral response are as follows:

Make sure you know the difference between the following two terms:

• Clonal selection - The B cell with the correct antibody is selected for cloning (by being activated by a T helper cell).
• Clonal expansion - The division of specific B cells to produce genetically identical clones.

Primary and secondary immune response

The body's response to an infection depends on whether the specific pathogen has been encountered before or not.

There are two types of immune response:

1. Primary immune response - This takes place when the body is exposed to a pathogen for the first time. This response is slow and the infected individual experiences symptoms of the disease.
2. Secondary immune response - This takes place when when the body has been exposed to the same pathogen before. This response is much faster and stronger and pathogens are destroyed before any symptoms appear.

The graph below shows how the concentration of antibodies changes as the body is exposed to a pathogen on two separate occasions.

Primary immune response:

1. The production of antibodies is slow after exposure to the pathogen (longer lag phase).
2. The concentration of antibodies increases slowly.
3. This is because there are very few B cells that are specific to the pathogen's antigens.
4. It takes time for the B cells to divide into plasma cells to produce the correct antibody, so the individual experiences symptoms of the disease.
5. During this process, some B cells divide into memory cells to make the individual immune to this disease.

Secondary immune response:

1. The production of antibodies is much quicker after exposure to the pathogen (shorter lag phase).
2. The concentration of antibodies increases quickly.
3. This is because memory B cells recognise the pathogen's antigens and quickly divide into plasma cells.
4. These plasma cells secrete larger numbers of antibodies to quickly destroy the pathogen before the individual experiences any symptoms.
5. Memory T cells are also activated to divide into T killer cells to destroy the pathogen.

Comparing the primary and secondary immune response

Autoimmune diseases

Sometimes the immune system cannot recognise 'self' antigens (the antigens present on the body's own cells) and starts to attack them. This occurrence is known as an autoimmune disease and leads to the breakdown of healthy tissues.

Examples of autoimmune diseases include:

• Type 1 diabetes - The immune system attacks the insulin-secreting cells of the pancreas, causing a lack of insulin.
• Lupus - The immune system attacks cells in the connective tissues, causing inflammation.
• Rheumatoid arthritis - The immune system attacks cells in the joints, causing pain and inflammation.