Life is always full of surprises, I suppose that is the way it is supposed to be otherwise if everything went always as planned then there would be no innovation.
So it was with surprise that I read an article about house dust mites and vitiligo in the September edition of the British Journal of Dermatology.
[Bzioueche H, Boniface K, Drullion C et al. Impact of house dust mite in vitiligo skin: environmental contribution to increased cutaneous immunity and melanocyte detachment. Br J Dermatol 2023;189:312-326.]
What is a house dust mite?
If you’ve never heard of these before, they are a mite which lives pretty much wherever humans live indoors. Without them, we would probably be wading through the dead skin cells that we shed every day as the house dust mites eat them all up. They love to live in soft furnishings such as carpets, sofas, beds, cushions, soft toys etc. The warm, humid environment of a home, especially with wall-to-wall carpets and central heating would be a house dust mite’s idea of heaven and indeed their population numbers explode when the central heating is turned on, usually around mid to end of October.
So how do they cause problems?
Well, people can become allergic to them. The commonest species is Dermatophagoides pteronyssinus (Der p) and it is associated with respiratory and skin allergies ie in asthma, hayfever and eczema. It can be found as part of the normal skin microbiota and can often found buried deep in hair follicles.
The house dust mite (HDM) contains enzymes such as proteases and other agents which are all known to be allergic triggers, can modulate immune systems and also disrupt the cells lining airways and the junctions between skin cells.
What has this got to do with vitiligo?
Well this is what is surprising. Vitiligo is a skin condition characterised by an autoimmune process which causes detachment of the pigment producing cells in the skin (the melanocyte) resulting in pale patches and skin depigmentation. A protein called matrix metalloproteinase (MMP) – 9 is implicated in this.
The authors of this study comment that the shift of onset of vitiligo from childhood to adulthood in the last 30 years cannot be explained by genetic factors alone and that there must be an environmental trigger too. They postulate that HDM could be this environmental trigger.
What does their study show?
It was a small study; 5 vitiligo patients and 5 non-vitiligo patients who just happened to come to dermatology clinic. They biopsied vitiligo and non-vitiligo skin in the patients with vitiligo and took samples from healthy abdominal skin and obtained skin cells (keratinocytes) from these. They also used skin from plastic surgery waste as an ex vivo model.
All were exposed to 24 hours of HDM and the proteins or cytokines created were measured.
And their results?
Skin cells from patients with vitiligo were 100 x more sensitive to HDM compared to healthy skin cells. HDM exposure also increased the number of detached melanocytes in both healthy and vitiligo skin but the change was more pronounced in vitiligo skin. This changed was mediated by MMP-9.
So the future?
Clearly more work needs to be done but it is exciting to think that MMP-9 inhibitors might present a new treatment option for patients with vitiligo.
Dr Sandy Flann, Consultant Dermatologist.