Characterization of cell subpopulations of the thymus by a hydrophobic fluorescent probe: 1-anilino-8-naphthalene sulphonate.

1-anilino-8-naphthalene sulphonate (ANS) is a hydrophobic fluorescent probe. ANS is not fluorescent in water or in RPMI 1640 medium, but it becomes fluorescent when bound to hydrophobic components of cells. The binding of ANS to mouse thymocytes shows that two cell subpopulations are identified, which differ in their emission wave-lengths, as reflected by their distinct 'blue' and 'green' fluorescence. This difference correlates with the DNA content of cells and this technique may characterize thymic cells in the G1 or in the S-G2 phases of the cell cycle in a quick and simple way.