A Study in Participants With Moderate to Severe Psoriasis

Inclusion Criteria Common to Both Part A: * Participant must have active plaque psoriasis covering at least 10% body surface area and a PASI score of at least 12 at screening and at randomization. * Participant is a candidate for systemic therapy * Participant has a Static Physician's Global Assessment (sPGA) score of at least 3 at screening and at randomization Inclusion Criterion Specific to Part B * Participant has completed the treatment period for part A (at least through week 20) Inclusion Criterion Specific to Part C * Participant has completed the treatment period for part B Exclusion Criteria Common to Part A, B and C: * Participant has pustular, erythrodermic and/or guttate forms of psoriasis * Participant has had a clinically significant flare of psoriasis during the 12 weeks prior to study entry * Participant has recently used any biologic agent/monoclonal antibody within the following washout periods: etanercept \>28 days, infliximab or adalimumab \>56 days, alefacept \>60 days, ustekinumab \>8 months, or any other biologic agent/monoclonal antibody \>5 half-lives prior to baseline * Participant has received systemic psoriasis therapy (such as psoralen and ultraviolet A \[PUVA\] light therapy, cyclosporine, corticosteroids, methotrexate, oral retinoids, mycophenolate mofetil, thioguanine, hydroxyurea, sirolimus, azathioprine) or phototherapy (including ultraviolet B or self-treatment with tanning beds) within the previous 4 weeks; or had topical psoriasis …