What causes psoriasis?

Detail by Ine C., on Flickr"><img src="http://farm3.staticflickr.com/2887/12268447975_cd3285ef91.jpgScientists do not yet fully know the cause of psoriasis; neither do they fully agree on what triggers the ailment. They do, however, have lots of good ideas:

Psoriasis is one of the most common long-term skin-related immune diseases in adults and has been around since ancient times (it used to be mistaken for leprosy). It is experienced as scaly, itchy and inflamed areas on the skin known as ‘plaques’, and can manifest as several different types. Psoriasis is a disease resulting from the immune system not behaving normally. Rather than attacking invaders, white blood cells trigger an inflammatory response (much like an allergic reaction) in the skin.

Medics and researchers have considered genetic factors which may predispose the body and immune system to increased inflammation. This tendency for psoriasis may be worsened by a host of other factors – such as diaper rash as in the case of childhood psoriasis. Other triggers include stress, pathogens such as Streptococcus, skin injuries and certain drugs. Suddenly stopping corticosteroid (‘Steroid’) treatment, which is usually prescribed to reduce symptoms, can sometimes result in a worsening called the ‘rebound effect’. This is particularly problematic as the body may become “addicted” to corticosteroid treatment, requiring continually higher dosages to keep the ailment at bay.

The interplay between a person’s genetics, what ‘environmental factors’ they are exposed to and their immune system is complex. Read on to dig deeper…

What goes on in the badly behaved immune system in psoriasis

The symptoms of psoriasis – in other words the inflammation – can be explained by the activation of the immune system’s cells. These include what are known as the T cells, macrophages and dendritic cells (DCs). These cells work to look for, identify and destroy foreign (or ‘non-self’) materials in the body while ignoring normal (or ‘self’) materials. Macrophages are cells which swallow and destroy the ‘bad’ materials (like Pac Man), breaking them up into very small pieces of proteins called antigens. The antigens are then used to attract ‘helper cells’ (a type of T cell). Amongst other things, T Helper cells secreting cytokines – chemicals which are like the “call-to-arms” for the rest of immune system. The making of antigens helps the body identify what materials are dangerous and should be eliminated. DCs are fascinating cells found in the areas of the body such as the stomach, skin and mouth that do similar things as macrophages. They regularly come into contact with outside materials – also engulfing and breaking down foreign materials to show them (in the form of antigens) to the T cells. In a healthy person, this system of macrophages, DCs and T cells functions beautifully, however, in the case of a person with psoriasis, these cells recognise harmless substances in the skin as a threat.

The genes of a person plays a large role in this faulty immune system functioning. In 2007 an article, Pathogenesis and Therapy of Psoriasis, explained in detail the pathways and cells involved in psoriasis. (Well worth reading for the seriously interested.) Several genetic errors (mutations) have been found in people with psoriasis. The mutations are known to mess with the major histocompatibility complex (MHC) – the machinery by which white blood cells present broken bits of protein (antigens) to T cells. Somehow the malfunctioning MHC triggers T cells to make lots of the cytokines associated with inflammation.

Question from Miles via Facebook

Answer by Janske Nel

Find out more about treatment for psoriasis here

The Psoriasis Association for further information

Image source: Ine C on Flickr

Article by Janske Nel

February 13, 2014

Janske Nel is currently busy with her second year of a Master’s in Nanotechnology, centred specifically on nano-oncology, at the University of the Western Cape, South Africa. She shows no fear in the face of spiders, snakes or long hours in the laboratory, but shudders at the thought of books left face down.

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