Electrophoretic analysis of cell subpopulations in the mouse thymus as a function of age.

The development of the cellular composition of the mouse thymus has been followed by means of electrophoretic mobility (EPM) analysis from birth to the age of 2 years. Four cell subpopulations were identified which differed in their surface charge as reflected by their distinct mean EPM and in their time of appearance during the course of life. A first electrophoretically slow-moving subpopulation (mean EPM = 0.92 μm sec Vcm), constituted the majority of newborn thymus cells but was progressively replaced by a slower-moving subpopulation (mean EPM = 0.80 μm sec Vcm). The fast-moving cells included a subpopulation with a mean EPM = 1.10 μm sec V cm, which was already visible at birth and another subpopulation with a mean EPM = 1.25 μm sec V cm, which appeared only at the 3rd week after birth. These two fast-moving subpopulations, and particularly the latter one, tended to increase in proportion as the mouse grew older. The biological significance of these four thymus cell subpopulations and of their age-related quantitative changes is discussed and on the basis of their chronological relationships a possible pattern of differentiation is suggested.