Abstract
Background: UV radiation exposure has immunosuppressive effects in humans. Low environmental UV radiation exposure is associated with multiple sclerosis risk. Narrowband UVB phototherapy is an established treatment for psoriasis, and is under investigation in people with clinically isolated syndrome (CIS) at risk of developing MS.
Objective: To determine whether systemic leukocyte phenotypes in blood are significantly altered by a short course of narrowband UVB phototherapy in people with CIS.
Methods: 20 participants with CIS were recruited and half received narrowband UVB phototherapy in 24 sessions over 2 months. Peripheral blood mononuclear cells (PBMC) were collected at baseline, and 1, 2, 3, 6 and 12 months after enrolment. Multicolour flow cytometry was used to identify T cell, B cell, monocyte, dendritic cell, and natural killer cell subsets. The effects of phototherapy on the frequencies of PBMCs were examined using linear regression.
Results: Significant differences in the frequencies of PBMC phenotypes were detected between treated and untreated individuals during phototherapy, including in subsets of B cells, monocytes and T cells. No effects were detected after phototherapy treatment ceased. The largest treatment effects were detected in B cell subsets, where phototherapy was associated with significantly higher naïve B cell frequency and significantly lower frequency of switched memory B cells.
Conclusions: Narrowband UVB phototherapy may contribute to immune suppression through regulation of systemic leukocyte phenotypes in people with CIS.