Additional Study Information: Atacicept is an investigational drug that is being evaluated for the treatment of patients withimmunoglobulin A nephropathy (IgAN). Investigational means that it has not been approved by anyhealth authority (government authorities) such as the US Food and Drug Administration (FDA) and isstill being tested for safety and effectiveness. Information gathered from this study will be sent to thevarious health authorities. There are two parts to this study. Part A will look at how safe the study drug is, and what potential side effects it may cause. It will also look at what the study drug does to the body (known as pharmacodynamics), how the body processes the study drug (known as pharmacokinetics), and how your immune system responds to the study drug. Part B will look at how effective the study drug is at reducing certain symptoms of IgAN when it is used at different doses. In particular, it will look at whether the study drug can reduce the amount of protein passed in your urine as a result of IgAN. The study will also look at how the study drug affects the function of your kidneys, how safe the study drug is, and what side effects it causes in patients with IgAN. Both parts of the study will compare the study drug to a placebo (something that looks the same as the study drug but contains no active medication). Placebos are used in clinical research studies to check that any effects seen from the study drug are real.