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 screening

- 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 screening

- Use of unstable dose of non-steroidal anti-inflammatory drugs (NSAIDs) within 14 days
prior to assignment to treatment

- 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 screening

- 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 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