Two major immune system genes under investigation are interleukin-12 subunit beta ( IL12B ) on chromosome 5q , which expresses interleukin-12B; and IL23R on chromosome 1p, which expresses the interleukin-23 receptor, and is involved in T cell differentiation. Interleukin-23 receptor and IL12B have both been strongly linked with psoriasis.  T cells are involved in the inflammatory process that leads to psoriasis.  These genes are on the pathway that upregulate tumor necrosis factor-α and nuclear factor κB , two genes involved in inflammation.  Recently, the first gene directly linked to psoriasis has been identified. A rare mutation in the gene encoding for the CARD14 protein plus an environmental trigger was enough to cause plaque psoriasis (the most common form of psoriasis).  
Phototherapy (light therapy) : Ultraviolet (UVL) light, a portion of the solar spectrum with wavelengths between 290-400 nm, can have beneficial effects on psoriatic skin presumably by altering certain immune functions. Disease that is considered too extensive to be treated by topical approaches, that is usually greater than 5%-10% of the total body surface area, is an appropriate indication for this sort of treatment. Resistance to conventional topical treatment is another indication for light therapy. Although normal sunlight contains these wavelengths, self-exposure to sunlight must be done in under controlled conditions to minimize burns. In a physician's office, control of the amount of light energy administered to each patient is essential. Medical light sources use special wavelengths of light and timers to assure the correct dosage of light. Sunlamps and tanning booths are not acceptable substitutes for medical light sources. Ultraviolet light from any source is known to produce skin cancer , but this side effect is minimized when the light is appropriately administered in a physician's office.