B cell (IMAGE) Howard Hughes Medical Institute Caption Rheumatoid arthritis causes pain and inflammation in the joints. B cells (one shown here) play a role in the disease. These cells may activate PRIME cells, the newly discovered cells that appear in the blood just before an attack of symptoms. Credit National Institutes of Allergy and Infectious Diseases, National Institutes of Health Usage Restrictions Must use credit. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.