Lymphocytes proliferate and differentiate in response to various concentrations of different antigens. The ability of the B cell to respond in a specific, yet sensitive manner to the various antigens is achieved with the use of low-affinity antigen receptors. The CD19 gene encodes a cell surface molecule that assembles with the antigen receptor of B lymphocytes in order to decrease the threshold for antigen receptor-dependent stimulation. [Wiki]

The stated application concentrations are suggested starting points. Titration of the CD19 antibody may be required due to differences in protocols and secondary/substrate sensitivity.

Store the CD19 antibody at -20oC.