Our immune system does an awesome job (most of the time) of fighting off pathogenic bacteria and viruses. But to fight off these pathogens, the body needs to know that they are the bad guys. This is where the HLA system comes in.
The IL17 gene codes for an important part of the immune system. When it is overactive, IL-17 can contribute to the risk of autoimmune diseases including rheumatoid arthritis and inflammatory bowel disease.
Psoriasis is an autoimmune condition that causes dry, sometimes itchy patches of skin. It is caused by the immune system attacking your skin cells, speeding up the turnover of the cells. Genetics plays a role in your susceptibility.