Your body’s immune system is supposed to protect you from diseases. When it’s working how it should, immune cells identify and attack invaders like bacteria and viruses. But when you have an autoimmune disease, cells in your immune system go haywire. With psoriasis, your T cells (a type of white blood cell) become highly active and attack skin cells by mistake. Then other parts of your immune system spring into action. Inflammation happens, and skin cells grow too fast. This is where immune system blood cells (T-cells) collect in the skin. The immune system activity stimulates skin cells to reproduce rapidly, producing silvery, scaly plaques on the skin.