The purpose of this study is to assess how safe, effective, and tolerable ABBV-547 is in adult participants in the United States and Japan.

There will be 2 parts to this study. In Part 1, participants are placed in one of 7 groups where they will receive ABBV-547 at different doses or placebo. There is a 1 in 4 chance participants will receive placebo. In Part 2, participants are placed in one of 3 groups where they will receive ABBV-547 at different doses or placebo. There is a 1 in 7 chance participants will receive placebo. Approximately 121 adult participants will be enrolled at approximately 21 sites in the United States and Japan.

Participants will be administered one dose of ABBV-547 or placebo.

There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires.

Inclusion Criteria:

• A condition of general good health, based upon the results of a medical history, physical examination, vital signs, laboratory profile and a 12-lead electrocardiogram (ECG).
• Part 1: BMI is >= 18.0 to <= 29.9 kg/m^2 after rounding to the tenths decimal at Screening. BMI is calculated as weight in kg divided by the square of height measured in meters.
• Part 2: must have discontinued use of phototherapy (e.g., UVA or UVB) at least 2 weeks prior to the baseline visit (Day 1) and PUVA phototherapy at least 4 weeks prior to the baseline visit (Day 1).

Exclusion Criteria:

• History of any clinically significant sensitivity or allergy to any medication or food.
• Part 2: uses any herbal supplements within the 2-week period prior to study treatment administration.
• Part 2: received any biologics including investigational agents within 2.5 half-lives prior to Baseline.