CD19

CD19 is a cell-surface molecule typically found on the B cell. It has a molecular weight of >120 kDa.

It is expressed on follicular dendritic cells and B cells. In fact, it is present on B cells from earliest recognizable B-lineage cells during development to B-cell blasts but is lost on maturation to plasma cells.

It primarily acts as a B cell co-receptor in conjunction with CD21 and CD81.

Upon activation, the cytoplasmic tail of CD19 becomes phosphorylated which leads to binding by Src-family kinases and recruitment of PI-3 kinase.