Phase 1 Study to Evaluate the PK, Safety, Tolerability of BIIB023 in Chinese, Japanese, and Caucasian Healthy Volunteers

Inclusion Criteria: * Must have the ability to understand the purpose and risks of the study \& provide signed \& dated informed consent. * Chinese, Japanese or Caucasian subjects * Subjects of childbearing potential must practice effective contraception during the study and 3 months after their last dose of study treatment. * Must have a BMI within the range of 18.5 to 25 kg/m2. * Must be willing to abstain from using tobacco and tobacco-containing products during the in-clinic period. * Must be willing to limit alcohol intake to no more than 2 units per day throughout the duration of the study (with some stricter exceptions at various timepoints). * Must be deemed healthy as determined by the Investigator, based on assessments at Screening and Day -1. Exclusion Criteria: * Known to have a positive test result for Human Immunodeficiency Virus (HIV) antibody. * Known history of hepatitis C or hepatitis B virus. * History of tuberculosis (TB) or a positive QuantiFERON®-TB Gold test. * Subjects with a history of carcinoma in situ and malignant disease. (with the exception of basal cell carcinoma that has been completely excised prior to study) * History of clinically important severe allergic or anaphylactic reactions. * Known allergy to components of the BIIB023 formulation. * History of any clinically important cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, and renal, or other major disease, as determined by the Investigator. * Abnormal hematology or blood chemistry values at Screening or Day -1, as determined by the Investigator. * Serious infection (e.g., pneumonia, septicemia) within the 2 months prior to Screening. * History of drug or alcohol abuse (as defined by the Investigator) within 6 months prior to screening, and/or a positive urine drug screen (without a medically indicated rationale) or positive alcohol breath test at Screening or on Day -1. * Active bacterial or viral infection and fever \>38°C within 48 hours prior to study treatment administration. * Female subjects who are pregnant, currently breastfeeding, or attempting to conceive during the study. * Surgery within 3 months prior to Day -1 or any surgical procedure planned during the course of the study * Previous exposure to BIIB023. * Treatment with another investigational drug , device, or approved therapy for investigational use within 30 days prior to Day -1, or 7 half lives of the investigational product, whichever is longer * Treatment with any prescription medication within 2 weeks before Day -1 with the exception of oral contraceptives for women of childbearing potential. * Treatment with any nonprescription medicinal products (including vitamin/mineral/herbal containing preparations but excluding acetaminophen) within the 7 days prior to study treatment. * Vaccination within 4 weeks of study treatment. * Blood donation (1 unit or more) within 1 month prior to study treatment or plasma donation within 7 days prior to study treatment. * Alcohol use within 48 hours prior to study treatment or during the In-Clinic period. * Current enrollment in any other study treatment or disease study. * Inability to comply with study requirements. * Vigorous exercise (as determined by the Investigator) within 72 hours prior to any study visit. * Other unspecified reasons that, in the opinion of the Investigator or Biogen Idec, make the subject unsuitable for enrollment.