A Study to Evaluate the Safety, Pharmacokinetics and Pharmacodynamics of UCB0159 in Participants With Mild to Moderate Psoriasis, Single Dose Pharmacokinetics and Safety in Healthy Participants.

Inclusion Criteria:

All Participants (healthy and participants with mild to moderate plaque PSO):

• Participant is male or female, aged >=18 years to \<=70 years at Screening.
• Participant is considered reliable and capable of adhering to the protocol.
• Female participants must either be postmenopausal, permanently sterilized or congenitally sterile. Female participants of childbearing potential must agree to use a highly effective method of birth control during the study period (from dosing until the Safety follow up (SFU) Visit) and for a period of 6 months after dosing of investigational medicinal product (IMP).
• Male Participant confirms that during the study period and for a period of 6 months, or, when having sexual intercourse with a woman of childbearing potential, a method of efficient contraception will be used, including a barrier (eg, condom without spermicide or fat- or oil containing lubricants) AND an additional highly effective contraceptive method (as listed below) by the female partner.
• Participant has a body mass index between 18 and \<=35kilograms (kg)/m\^2 and a minimum body weight of 45kg (female participants) and 50kg (male participants) at Screening.
• Participant is in good physical and mental health, in the opinion of the Investigator, determined on the basis of medical history and general clinical examination at Screening and at Baseline.

Participants with mild to moderate plaque Psoriasis:

• Confirmed diagnosis of mild to moderate plaque-type Psoriasis for at least 6 months involving \<10 percent (%) of body surface area (BSA) (excluding the scalp).
• Minimum of 2 psoriatic lesions with at least 1 plaque in a site suitable for biopsy.

Exclusion Criteria: All Participants (healthy and participants with mild to moderate plaque PSO):

• Participant has received an IMP within the last 3 months or 5 half-lives prior to Screening, whichever is longer.
• Participant has a known hypersensitivity reaction to any components of the IMP (polysorbate 80, histidine, and/or proline).
• Participant has donated more than 400 milliliters (mL) of blood or blood products within 90 days prior to check in (Day -2) or plans to donate blood during the study.
• Participant has an active or recurrent clinically significant infection (eg, sepsis, pneumonia, or abscess) or has had a serious or opportunistic infection (resulting in hospitalization or requiring parenteral antibiotic treatment) within 6 weeks prior to IMP administration.
• Participant with known active tuberculosis (TB) disease, with a past history of active TB involving any organ system, participant with current or history of nontuberculous mycobacterial (NTMB) infection despite prior or current therapy, participants at high risk of acquiring TB infection.
• Participant with latent TB infection (LTBI).
• Participant has received live attenuated vaccination within 8 weeks prior to Screening or intends to have such a vaccination during the course of the study or within 12 weeks after the dose of study drug.
• Participant has a positive hepatitis B surface antigen or positive hepatitis C antibody result within 3 months prior to Screening.
• Participant has a positive test for human immunodeficiency virus (HIV) antibody.

Participants with mild to moderate plaque Psoriasis:

• Participant has received systemic nonbiologic PSO therapy (methotrexate [MTX], steroids, or cyclophosphamide), phytotherapy, or psoralen plus ultraviolet A (PUVA)/ultraviolet A (UVA) phototherapy within 4 weeks prior to Screening.
• Participant has received alefacept within 24 months prior to Screening.
• Participant has received treatment with biological agents other than alefacept, eg, adalimumab, efalizumab, etanercept, infliximab, ustekinumab, or bimekizumab within 12 weeks prior to Screening.
• Participant has a history or current evidence of autoimmune disease other than PSO
• Participant has any other acute or chronic illness which, in the opinion of the Investigator or Study Physician, could pose a threat or harm to the Participant.