[Suppressive cells induced by cyclophosphamide in the spleen of C3H mice]

The spleen cell population of C3H/He mice injected with a single sublethal dose of cyclophosphamide (CY) was analysed. An initial atrophy was followed by a considerable hypertrophy and a progressive return to normal. During the phase of spleen atrophy, both B and T cell compartments were depleted. During regeneration, the percentage of Ig+ cells increased rapidly, and at the peak of splenomegaly, the percentage of Ig+ cells was high while no Thy1-2+ cells were detectable. The peculiar points of histology were disappearance of normal T and B compartments, substituted by a layer of lymphoid cells. During the phase of splenectomegaly, the in vitro reactivity of spleen cells to the mitogens PHA and LPS was drastically decreased. Furthermore, the spleen cell population from CY treated mice contained suppressor cells, capable of inhibiting the in vitro reactivity of normal lymphocytes to these mitogens and the multiplication of tumour cells in culture. These cells were adherent, Ig+, Thy1-2- cells. They developed in CY treated T deprived mice. After velocity sedimentation the suppressive activity was detected in the 6 mm/h fraction.