Moderate to Severe Plaque Psoriasis with Scalp Involvement

- Must provide written informed consent before any study-specific procedure - Be male or female greater than or equal to 18 years of age at time of screening - Has stable moderate to severe plaque psoriasis for at least 6 months - Affected body surface area (BSA) greater than or equal to 10% - Psoriasis Area and Severity Index (PASI) score greater than or equal to 10 - At least 30 percent affected scalp surface area - Psoriasis Scalp Severity Index (PSSI) score greater than or equal to 15 - Candidate for systemic therapy or phototherapy in the opinion of the investigator - Negative test for hepatitis B surface antigen, hepatitis C antibody, and Human Immunodeficiency Virus (HIV) - Negative serum pregnancy test for female subjects (unless 3 years post menopausal or surgically sterile) - Willing to use medically acceptable form of birth control for duration of study - Negative Purified Protein Derivative (PPD) within 30 days prior to first dose of study drug

- Any active infection - Significant concurrent medical conditions, including: Insulin dependent diabetes mellitus; Congestive heart failure; Myocardial infarction within last year; Unstable angina pectoris; Uncontrolled hypertension; Severe pulmonary disease [requiring oxygen therapy or hospitalization]; Systemic lupus erythematosus; Multiple sclerosis or any other demyelinating disease; Active malignancy - Any condition, in opinion of study doctor, that might cause this study to be detrimental to subject - History of cancer within 5 years before first dose of study drug - Skin conditions other than psoriasis that would interfere with evaluations of the effect of study medications on psoriasis - Presence of guttate, erythrodermic or pustular psoriasis - Use of topical cyclosporine or calcineurin inhibitors within 14 days of first dose of study drug - Use of tar shampoos within 14 days of first dose of study drug - Use of following therapies within 28 days of first dose of study drug: IV or oral cyclosporine or calcineurin inhibitors, Ultraviolet Light A therapy, Psoralen plus ultraviolet A radiation, Oral retinoids, Ultraviolet Light B therapy, Topical steroids or steroid shampoo, Topical vitamin A or D analog preparations, Anthralin, other systemic psoriasis therapy, cyclophosphamide, sulfasalazine, anakinra - Use of Alefacept (Amevive), Efalizumab (Raptiva), Anti-tumor necrosis factor (TNF) biologic therapies within 3 months of the first dose of study drug. Prior anti-TNF use will not be permitted if discontinued due to lack of efficacy, an adverse event, or non-compliance. - Use of interleukin (IL)-12/IL-23 within 6 months of the first dose of study drug - Participation in another clinical trial within 90 days or 5 half-lives (whichever is longer) of randomization - Laboratory abnormalities at screening: hemoglobin less than 11 g/dL, platelet count less than 125,000/mm^3, white blood cell count less than 3,500 cells/mm^3, aspartate aminotransferase (AST)/alanine aminotransferase (ALT) greater than or equal to 1.5 x the upper limit of normal, any other laboratory abnormality which will prevent patient from completing the study or interfere with interpretation of study results - Patient is pregnant or breast feeding - Presence of any condition that could compromise the patient's ability to participate in the study, such as a history of substance abuse or psychiatric condition