Mast cell chymase in experimentally induced psoriasis.

Mast cell chymase can have a pro-inflammatory or an immunosuppressive function in psoriasis, but the outcome may depend on the level of chymase activity. Therefore, mast cells showing chymase activity (Chyact ) and immunoreactivity (Chyprot ) were studied during the Köbner reaction (0 days, 2 h, 1 day, 3 days and 7 days) of psoriasis induced by the tape-stripping technique. Also, the effect of recombinant human chymase (rh-chymase) or human LAD2 mast cells (LAD2) on the (3) H-thymidine uptake of psoriatic peripheral blood mononuclear cells (PBMC) or total T cells was studied. The Chyact /Chyprot ratio tended to be higher in all time-point biopsies in the Köbner-negative (n = 10) than -positive (n = 8) group (P = 0.073), although chymase activity decreased significantly at 2 h to 1 day only in the Köbner-negative group. rh-chymase (0.05-0.5 μg/mL) stimulated to a varying extent PBMC in eight out of nine cultures, but in all cultures 5 μg/mL rh-chymase turned the stimulation towards inhibition. The effect of rh-chymase on T cells varied from stimulation to inhibition, but in 11 of 15 cultures rh-chymase, at least at 5 μg/mL, produced a change to inhibition. In co-cultures, LAD2 inhibited PBMC in the absence of soybean trypsin inhibitor (SBTI). In the presence of SBTI, LAD2 stimulated PBMC in the majority of seven cultures. In summary, the psoriatic immunopathogenesis may be promoted at low, but controlled at high, activity status of chymase.