Abatacept a protein that prevents your body’s immune system from attacking healthy tissues such as joints. The immune system helps your body fight infections. In people with autoimmune disorders, the immune system mistakes the body’s own cells for invaders and attacks them. Abatacept is used to treat the symptoms of rheumatoid arthritis, and to prevent joint damage caused by these conditions. abatacept is for adults and children who are at least 2 years old. Abatacept is also used to treat active psoriatic arthritis in adults. Abatacept is not a cure for any autoimmune disorder and will only treat the symptoms of your condition. Abatacept may also be used for purposes not listed in this medication guide.