Chloroquine stimulates the mitogen-driven lymphocyte proliferation in patients with psoriasis.

Chloroquine is known to exacerbate psoriasis. Since immunological stimuli are considered to be important for the pathogenesis of psoriasis, we compared the effects of chloroquine on cell-mediated immunity in 15 healthy control individuals and 15 patients with psoriasis. We employed the spontaneous and phytohemagglutin (PHA)-induced uptake of 3H-thymidine to measure lymphocyte proliferation. Chloroquine was added to the cultures at concentrations ranging from 0.022 to 220 microM. We found that both spontaneous and PHA-driven lymphocyte proliferations were significantly lower in patients with psoriasis (p < 0.002). The spontaneous blastogenesis in both controls and patients remained stable under chloroquine. In PHA-driven cultures in controls, 0.022-2.2 microM chloroquine had no effect, higher concentrations of the drug suppressed proliferation. In patients, 22 microM chloroquine surmounted the suppression of the PHA-induced proliferative response found in controls; moreover, 2.2-0.022 microM chloroquine increased lymphocyte proliferation by > 300% (p < 0.002). Our data indicate that in psoriasis the lower lymphocyte transformation is abnormally stimulated by the addition of pharmacological doses of chloroquine.