For Part I : Healthy male and female subjects 18 to 65 years of age inclusive; For Part II: Chronic plaque-type psoriasis (with or without arthritis) diagnosed for at least 6 months before enrollment including at least one plaque accessible for OFM with at least moderate severity ; Key exclusion criteria for Part I and Part II: Women of child-bearing potential unwilling to use effective contraception; History of an ongoing, chronic or recurrent infectious disease, or evidence of tuberculosis infection as defined by a positive TB-test at screening; For Part I: Use of any prescription drugs, herbal supplements, within 4 weeks prior to initial dosing For Part II: Ongoing use of concomitant psoriasis treatments. Washout periods have to be adhered to.