The purpose of this study is to assess the safety, tolerability, immunogenicity, and clinical effects of AMG 811 following single subcutaneous dose administration in subjects with moderate to severe psoriasis.

Inclusion Criteria:

• 18 - 55 years old inclusive at Screening
• Active but clinically stable, plaque psoriasis
• Psoriasis involving ≥ 10% of the body surface area
• A minimum PASI score of ≥ 10 obtained during the screening period
• Additional inclusion criteria apply

Exclusion Criteria:

• Active guttate, erythrodermic, or pustular psoriasis at the time of the screening visit
• Evidence of skin conditions other than psoriasis (eg, eczema) at the time of the screening visit or between the screening visit and study drug initiation that would interfere with evaluations of the effect of investigational product on psoriasis
• Any condition that, in the judgment of the investigator, might cause this study to be detrimental to the subject
• Additional exclusion criteria apply