A Study of LY3316531 in Healthy Participants and in Participants With Psoriasis

Inclusion Criteria: * Healthy Participants * Are overtly healthy males or females, as determined by medical history and physical examination * Females must be of non-childbearing potential * Are between 18 and 64 years of age, inclusive, at screening * Have a body mass index of 18.0 to 32.0 kilograms per meter squared (kg/m²) inclusive * Are reliable and willing to make themselves available for the duration of the study and are willing to follow study procedures * Psoriasis Participants: * Chronic plaque psoriasis based on an investigator confirmed diagnosis of chronic psoriasis vulgaris for at least 6 months prior to baseline * Meet psoriasis disease activity criteria * Are at least 18 years of age * Have a minimum body weight of 50 kilograms (kg) Exclusion Criteria: * Healthy and Psoriasis Participants * Have known or ongoing neuropsychiatric disorders * Have received live vaccine(s) (included attenuated live vaccines) within 28 days of screening or intend to during the study * Have had any malignancy within the past 5 years except for basal cell or squamous cell epithelial carcinomas of the skin that have been resected with no subsequent evidence of recurrence for at least 3 years prior to screening and cervical carcinoma in situ with no evidence of recurrence within 5 years prior to baseline * Show evidence of active or latent tuberculosis (TB) * Have presence of significant uncontrolled cerebro-cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrine, hematologic, neurologic or neuropsychiatric disorders or abnormal laboratory values at screening that, in the opinion of the investigator, pose an unacceptable risk to the participant if participating in the study or of interfering with the interpretation of data * Psoriasis Participants Only: * Have received treatment with biologic therapies for psoriasis (such as monoclonal antibodies, including marketed or investigational biologic therapy) * Prior or current use of biologics for indications other than psoriasis may be allowed with sponsor approval * Have received systemic nonbiologic psoriasis therapy within 28 days of baseline * Have received topical psoriasis treatment within 14 days of baseline