Fundamental fact about this disease: Plague Psoriasis
A common knowledge-base portal via Wikipedia provides just enough knowledge. I like webmd better as it looks closer to scientific oriented write up. The Mayo Clinic would provide much thorough and unbiased explanation for the disease.
From Mayo Clinic, Psoriasis triggers
Psoriasis typically starts or worsens because of a trigger that you may be able to identify and avoid. Factors that may trigger psoriasis include:
All about autoimmune related issues
Wikipedia on TNF-alpha, a cancer related protein: Tumor Necrosis Factor alpha