• Our immune system is our body’s own defence mechanism.
• The immune system makes antibodies and cells that fight infections.
• Normally, these antibodies don’t attack the body itself. But, if a person has an autoimmune disease, the immune system attacks bits of the body by mistake.
• PV is an autoimmune disease.
• The immune system of a patient with PV makes antibodies which attack the proteins that make up the skin and mucous membranes. These are called autoantibodies.
• The autoantibodies in PV attack proteins called desmogleins. Desmogleins are on the surface of the skin cells. They act as glue to stick the skin cells together keeping the layer of skin intact.
• So, when the autoantibodies attack desmogleins, the skin cells no longer stick together and get separated from each other ^5,6 . This is what causes the burn-like erosions or blisters that are typical of PV.
• There are several different types of desmogleins. In PV, all patients have antibodies which attack desmoglein 3 (the most important protein in the mouth) but patients with mucocutaneous PV also have antibodies which attack desmoglein 1 (the most important protein in the skin) ³ (see ‘What types of pemphigus are there?’).
• This explains why people who have PV desmoglein 3 antibodies tend to have mouth lesions only (mucosal PV), whereas those who have desmoglein 3 and 1 antibodies tend to get mouth and extensive skin lesions too, or mucocutaneous PV (see ‘What types of pemphigus are there?’).
• Although it is known that desmoglein antibodies cause PV, it is not known why people develop these autoantibodies in the first place. Genetic factors are believed to be important (see ‘Is pemphigus vulgaris hereditary?’) but it is likely that there are other factors which trigger PV (see ‘Does anything make pemphigus vulgaris worse?’).
• PV is one of many autoimmune diseases. Some more common ones include type I diabetes, vitiligo (white patches of skin) and some types of thyroid disease.

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