A Study of LY3090106 in Healthy Participants and Participants With Rheumatoid Arthritis (RA)

Inclusion criteria

for Healthy Participants:

• Males or non-pregnant females age 18 to 65 years
• Body Mass Index (BMI) of 18.5 to 32.0 kilograms per meter squared (kg/m^2)

Inclusion criteria

for Participants for RA:

• Diagnosis of at least mildly active adult-onset RA
• Positive anti-citrullinated protein (ACPA) antibodies or rheumatoid factor
• Regular use of MTX for at least 12 weeks and at a stable dose (10 to 25 mg/week) for at least 4 weeks prior to baseline
• American College of Rheumatology (ACR) Functional Class I, II or III

Exclusion criteria

for Healthy Participants:

• Have received biologic agents within 3 months or 5 half-lives
• Have surgery within 12 weeks prior to screening
• Known history of human immunodeficiency virus (HIV infection and/or positive human HIV antibodies)
• Have evidence of, or test positive for, hepatitis C virus or hepatitis B virus
• Have evidence of active infection or fever
• Have donated greater than 500 mL blood within 30 days prior to screening
• Smoke greater than 10 cigarettes/day or equivalent
• Have received live vaccine within 1 month of screening
• Have a history of allergy to monoclonal antibodies or severe drug allergies

Exclusion criteria

for Participants with RA:

• Have received prior or current treatment with biologic RA therapies
• Have received a live vaccine 28 days prior to screening or intend to receive a live vaccine during the course of the study
• Hemoglobin < 10 grams per deciliter (g/dL), platelet count < 100,000 cells/microliter (uL), total white blood cell count < 3000 cells/uL, neutrophil count < 2000 cells/uL, or lymphocyte count < 500 cells/uL
• Aspartate transaminase (AST) > 1.5 x upper limit or the normal range (ULN), alanine transamine (ALT) > 1.5 x ULN, creatinine > 1.5 mg/dL (114 micromoles/liter [uMol/L])
• Treatment with > 10 mg/day or unstable dose of oral prednisone or equivalent within 28 days of baseline
• Have required an increase in dose or a new prescription of narcotic within 28 days prior to randomization
• Have received any parenteral corticosteroids within 28 days before screening
• Treatment with any oral disease-modifying anti-rheumatic drugs (DMARDs) other than MTX within 4 weeks prior to baseline
• Any neurological, psychiatric, vascular, or system disorder that could also affect the evaluation of disease activity assessments. Anemia of chronic disease is allowed if hemoglobin > 10 g/dL
• Have rheumatic or systemic autoimmune disease other than RA or significant active systemic involvement secondary to RA. Participants with secondary Sjogren's syndrome are eligible.
• Uncontrolled arterial hypertension characterized by a confirmed systolic blood pressure of > 150 mm Hg or diastolic blood pressure > 90 mm Hg at screening or on day of study drug dosing
• Poorly controlled diabetes as defined by glycosylated hemoglobin (HbA1c) > 8.0% at screening
• Known history of human immunodeficiency virus (HIV infection and/or positive human HIV antibodies)
• Have evidence of, or test positive for, hepatitis C virus or hepatitis B virus