mature B cell memory B cell A memory B cell is a mature B cell that is long-lived, readily activated upon re-encounter of its antigenic determinant, and has been selected for expression of higher affinity immunoglobulin. This cell type has the phenotype CD19-positive, CD20-positive, MHC Class II-positive, and CD138-negative. Memory B-cells are also reportedly CD5-negative, CD10-negative, CD21-positive, CD22-positive, CD23-negative, CD24-positive, CD25-positive, CD27-positive, CD34-negative, CD38-negative, CD40-positive, CD43-negative, CD44-positive, CD45-positive, CD53-positive, CD80-negative, CD81-negative, CD86-positive, and CD196/CCR6-positive. cell memory B lymphocyte memory B-cell memory B-lymphocyte