Antigens

• Antigens are molecules (proteins and glycoproteins) that are present on the cell surface membrane of all cells.
• Antigens signal to the immune system if the cells are 'foreign'.

• Every cell has specific antigens.
• The antigens bind to complementary receptors on the cell surface membrane of the immune cells.
• If the antigens are 'foreign', this will induce an immune response.

• Not all antigens induce an immune response.
• Antigens can also signal if the cells are 'self' or they belong to the host organism.

• The immune system can respond to antigens in a number of ways:
• Lysozymes break down the foreign cells.
• Phagocytosis of the foreign cells.
• Production of antibodies that bind to the antigens and inhibit the functioning of the foreign cells.

• Sometimes the immune system fails to differentiate between self and non-self.
• This can lead to the development of autoimmune conditions. In these conditions, the body's own immune system attacks the body's cells.

An example of an autoimmune condition is myasthenia gravis.

• In myasthenia gravis, the body produces antibodies against the acetylcholine receptor.
• This receptor is found at the neuromuscular junction between nerves and muscles.
• So, symptoms of this condition include paralysis and muscle weakness.
• The first muscles that typically lose strength are those around the eye, leading to eyelid drooping,