Immunomodulation at the initiation of phototherapy and photochemotherapy

The numbers and function of circulating lymphocyte subsets are within normal ranges in patients with psoriasis and are not affected by 4 weeks of ultraviolet (UV) therapy, except for a suppression in natural killer (NK) cell activity. However, it is possible that immunomodulation might occur at the initiation of phototherapy with a return to control values on more prolonged UV exposure. Thus, in this study the responses of 15 patients with chronic plaque psoriasis undergoing broad-band UVB therapy, 10 narrow-band (311-313 nm) UVB therapy and 10 PUVA therapy were compared. In each case, samples were taken immediately before starting treatment and 1 week later. Broad-band UVB and PUVA therapy had no effect on NK activity, but a significant reduction was found in the group receiving narrow-band UVB. In vitro lymphoproliferative responses to mitogens and to herpes simplex virus antigens did not alter with therapy, except there was a significant increase in mitogen responses (at optimal mitogen concentrations only) in the narrow-band UVB group. Generally no alterations in overall percentages of circulating mononuclear cells were found in any group. Samples were taken from the epidermis of the forearm and back of the patients receiving narrow-band UVB for the quantification of urocanic acid (UCA) isomers. The total UCA concentration remained unchanged after 1 week of therapy, while the percentage of cis-UCA increased significantly at both sites in the majority of patients. However, this rise did not correlate with the decrease in NK cell activity and the two parameters may not be related causally.