The lymphocyte subpopulations activated by 2-ME in C3H/St spleen cell cultures were characterized by means of kinetic and cell separation techniques. The current experiments were designed to determine whether 2-ME potentiates the maintenance of an activated state in cells that had been triggered by environmental stimuli encountered by the intact animal, or whether this thiol compound is able to transform typical resting lymphocytes to an activated state. Kinetic experiments demonstrated that the high rate of nucleotide turnover seen initially in cultured cells was not directly accentuated. Rather, this turnover was found to subside normally before 2-ME-initiated activation of lymphocyte [3H] TdR uptake began. Studies in which cells were separated according to sedimentation velocity showed clearly that 2-ME responsiveness is a quality of small lymphocytes (s = 3.9 mm/hr) and not of large, activated cells. Moreover, when cells were separated on the basis of buoyant density, reactivity to this thiol compound was found to reside within cells of high density, strongly supporting the thesis that 2-ME activates a resting lymphocyte subpopulation and does not simply maintain an activated state acquired in vivo. The influence of antigenic milieu was evaluated directly in mice reared under germfree, specific pathogen-free, and conventional conditions. Lack or limitation of environmental antigenic exposure resulted in a significantly larger DNA synthetic response to 2-ME. This pattern was presumed to reflect a greater preponderance of unstimulated lymphocytes in the spleens of germfree and SPF mice.

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