This is a randomized, double-blinded, placebo-controlled adaptive, dose finding study to investigate the safety, tolerability, PK, PD and efficacy of single and repeat intravenous infusions of GSK315243A in patients with active rheumatoid arthritis. The study is divided into 2 parts: Part A is an adaptive, dose finding phase which will provide safety, tolerability, PK and PD on single intravenous infusions. Part B is a repeat dose phase which will provide safety, tolerability, PK, PD and efficacy following repeat intravenous infusions of a selected dose level.