B cells are a special type of white blood cell that produces antibody. Because the NMO-IgG antibody is believed to play a role in causing NMO disease or relapse, B cells that make NMO-IgG are considered targets for NMO therapy. For example, rituximab targets and eliminates certain types of B cells that may produce NMO-IgG antibody. B cell monitoring is often used for patients after receiving rituximab infusions, which are often four-to-six months apart.