The purpose of this study is to learn about the safety and effects of the study medicine (called PF-07985631) for the possible treatment of a kidney disease called IgA nephropathy. This study is seeking participants who * are male or female between 18 and 45 years of age (55 for Japanese/Chinese/multiple dose participants) * are deemed to be healthy Participants in this study will receive PF-07985631 or placebo. A placebo does not have any medicine in it but looks just like the medicine being studied. PF-07985631 or placebo will be given as a small needle injection (in the abdomen, thigh or back of the arm) or as an IV infusion in the arm (given directly into a vein) at the study clinic. Most participants will receive PF-07985631 or placebo one time. Some participants may receive PF-07985631 or placebo once a month for 3 months. The study will compare the experiences of people receiving PF-07985631 to those of the people who do not. This will help decide if PF-07985631 is safe and effective. Participants who take PF-07985631 or placebo only 1 time will take part in this study for about 4 months. During this time, they will stay at the study clinic for 11 to 14 days and will have 8 more study visits at the study clinic. Participants who take PF-07985631 or placebo more than once will take part in this study for about 6 months. During this time, they will stay at the study clinic for about 4 days a month 3 times and will have 10 more study visits at the study clinic. During study clinic stays and study visits, blood samples will be done and safety reviews completed.