Electrophoretic mobility and surface immunoglobin of albumin gradient fractionated mouse spleen cells.

Spleen cells from normal CBA mice, containing B and T lymphocytes, cyclophosphamide-treated CBA mice, containing almost exclusively T lymphocytes, and athymic nudemice, containing only B lymphocytes, were fracitonated by differential flotation in adiscontinuous albumin gradient. In all three cases, four density fractions were regularly obtained. The electrophoretic mobility (EPM), which allows distinction betweenslow-EPM (B) cells and fast-EPM (T) cells and the presence of surface immunoglobulins (sIg) detectable by direct immunofluorescence, characterizing B lymphocytes, were investigated on these fractions. Both B and T cells were recovered throughout the gradient, but in different proportions. Thus, B cells (slow-EPM, sIg-bearing) were enriched in the light density fractions while T cells (fast-EPM)were more numerous in the denser fraction. The mean EPM of slow-moving cells decreased, whereas that of fast-moving cells increased, as their buoyant density increased. Less nude spleen (B) cells were found to bear sIg in the light density fractions than in the denser fractions. These findings suggest the existence of lymphocyte subpopulations with distinct physicochemical properties which might represent stages in the maturation and differentiation of B- and T-cell lineages.