Fig. S1. Clinical measurement of the Mantoux test (MT). (a) The Mantoux test is characterized clinically by the presence of a localized area of erythematous indurated oedematous skin. MTs were induced on the volar aspect of the forearm. The MT peaks clinically 2–3 days after induration. (b) The erythema index was measured at baseline, on day 3 and at the time of sampling using a DermaSpectrometer. The mean of three measurements was recorded.

Fig. S2. Suction blister equipment. (a) A clinical grade suction pump was used for skin suction blister induction. The pump has a gauge allowing a consistent negative pressure to be applied to the skin. The VP25 Eschmann suction pump has sterile disposable tubing and liners that can be changed between volunteers. (b) The suction cup is applied to the skin and connected to the pump using a cut-down pipette tip. (c) Suction cups consisted of three main components: a template and cup made of nylon plus a see-through Perspex lid. Rubber O-rings fit around the lid and template so that the three components fit together, forming airtight seals. The size of template used can be changed according to the size of Mantoux test (MT) induration, i.e. 15-mm diameter template if >15 mm induration, 12·5-mm diameter template if 10–15 mm and 10-mm diameter template if <10 mm. The template apertures have bevelled edges. This is to ensure that skin is drawn comfortably into the suction cup during blister induction. The see-through lid allows the induction process to be observed and monitored.

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