 This is a first time in human, phase 1, randomized, blinded, placebo-controlled study to evaluate the safety, pharmacokinetics and pharmacodynamics of single ascending subcutaneous doses of MEDI5884 in healthy volunteers age 18-55. The study consists of 4 cohorts of increasing doses 8 subjects each and an optional Japanese American cohort 24 subjects for a total of 56 healthy subjects. The decision whether or not to dose escalate will be based upon data review by the Dose Escalation Committee. Subjects will be randomized 3:1 to MEDI5884 or placebo. Following screening, the study consists of a 3 day inpatient stay and follow up visits. The number of follow up visits depend on the cohort assigned. 