mature B cell antibody secreting cell plasmablast An activated mature (naive or memory) B cell that is secreting immunoglobulin, typified by being CD27-positive, CD38-positive, CD138-negative. FMA:84371 This cell type is compatible with the HIPC Lyoplate markers for 'plasmablast'. Plasmablasts are also reportedly CD48-positive, CD63-positive, CD229-positive, CD270-positive, CD319-positive, CD352-positive, CD361-positive, and IgD-negative. cell