B Cells express CD19 from very early stages, expression is only lost upon maturation into plasma cells. After maturing, the B cells migrate to secondary lymphatic organs and are subsequently activated directly by an antigen or through an antigen presenting cell. At this point they either become memory B cells or plasma B cells. Each B cell gives rise to a single species of antibody.

PPA's Human Normal CD19+ B cells are isolated from peripheral blood mononuclear cells by positive immunomagnetic selection. All peripheral blood is collected by leukaphresis in ACDA from fully consented IRB approved donors that test negative for HIV, HBV and HCV.