CTLA4 and psoriasis: In a mouse model of psoriasis (K5.hTGF-b1 transgenic mice) [26], 4-week PUVA treatment suppressed the IL-23/Th17 pathway while augmenting the frequencies of Th2 and IL-10 secreting Foxp3 + Treg, in a CTLA-4 dependent manner, and the levels of many inflammatory cytokines were reduced.