Identification and partial characterization of a unique marker for human basophils

A unique marker for human basophils is needed to precisely determine the involvement of this cell type in clinical disease. To search for a marker of the basophil secretory granule, mouse hybridomas were generated against purified human basophils and screened for basophil-selective Ab. One hybridoma (2D7) produced an IgG1 kappa Ab that labeled basophils, but not lymphocytes, monocytes, eosinophils, neutrophils, and mast cells by an indirect immunoperoxidase procedure. The pattern of basophil staining was cytoplasmic and granular by light microscopy. By immunogold electron microscopy, the 2D7 ligand was localized to secretory granules. Activated basophils showed reduced 2D7-dependent staining intensity, consistent with a secretory granule localization. Tissue sections of normal skin, lung, and bowel showed no reactivity with 2D7, consistent with the anticipated absence of basophils in these tissues. 2D7 staining of basophils was clearly distinct from metachromatic staining, which was presumably dependent on proteoglycan. Extracts of normal human basophils subjected to Western blotting with 2D7 exhibited two predominant bands at apparent molecular masses of 76,150 and 72,260 Da. In summary, the 2D7 ligand appears to be a specific marker for human basophils and may facilitate the assessment of basophil involvement in diseases such as asthma, anaphylaxis, and atopic dermatitis.