Immunocytochemical analysis of salivary epithelial cells. Cells were obtained from minor salivary glands (a–e) and the HSG cell line (f–i). Positive staining for cytokeratin 7 (a) and cytokeratin 19 (b) and the absence of staining with cytokeratin 20 (c) indicates the specificity of ductal epithelial cell origin. The absence of staining for myeloperoxidase (MPO) (d), CD45 (e), CD20 (f), CD3 (g) and smooth muscle actin (h) before (subpanels 1 in (d–h)) and after (subpanels 2 in (d–h)) stimulation with IFN-α excludes the possibility of contamination with myeloid cell. Positive staining with cytokeratin 7 (i) and the absence of staining with cytokeratin 20 (j) indicate the ductal epithelial origin of HSG cell lines. Negative staining with myeloperoxydase (MPO) (k) and CD45 (l) excludes the possibility of contamination with myeloid cells.