Fig 1: Microphotographs of the parental MDCK and cloned cell lines. A.Original MDCK (ATCC-CCL-34, NBL-2; +7 passages). B. Type-1 cells (clone 4F2; +5 passages after cloning): gentle polymorphic cells with a visible nucleus and very fine almost indistinguishable intercellular space, cells often develop large cytoplasmic area. C. Type-2 cells (clone 3D7; +4 passages after cloning): polygonal cells with almost invisible nuclei; the intercellular space is well developed, and contributes to a specific a mosaic-like appearance of the monolayer. D. Formation of the numerous liquid-filled structures, “domes”, visible as rounded refracting blisters on the monolayer of the Type-3 cells (clone 3E11; +11 passages after cloning).