The Alexa Fluor 647 goat anti—mouse IgG_2b is labeled with our exceptionally bright far-red—fluorescent Alexa Fluor 647 dye (which is spectrally similar to Cy5 dye) and is prepared from affinity-purified antibodies that react the with the Fc portion of the heavy chain of mouse IgG_2b. To minimize crossreactivity, the antibody has been adsorbed against mouse IgM, mouse IgA, pooled human sera, purified human paraproteins and mouse isotypes IgG₁, IgG_2a and IgG₃ prior to labeling. Fluorescence of this long-wavelength Alexa Fluor dye is not visible to the human eye but is readily detected by most imaging systems.