Serum collected from mice 6 hr after immunization with soluble antigens in Freund's complete adjuvant was able to induce various changes of the bone marrow-derived (B)-cell (γ globulin-carrying) and thymus-derived (T)-cell (θ-carrying) populations when incubated with spleen cells from unimmunized mice. First there was an overall increase (by 25%) of all the γ globulin-carrying cells. This increase could be accounted for by an identical increase of the cells carrying γG (7S γ2a) globulin on their surface. At the same time the cell population normally carrying γF (7S γ1) globulin decreased. These changes were detected by the reverse immune cytoadherence technique (RICA) with highly specific hybrid antibodies which detect one class of mouse γ globulins. Second, the treated spleen cells show a decrease of the T-cell population as detected by an anti-ϑ serum. This decrease was of a similar magnitude as the increase of the γG-carrying cells and involved about 40% of the ϑ-carrying cells. Thus the serum reproduces in vitro all the phenomena previously described as taking place in the spleen 6 hr after immunization. When the 6-hr serum from mice injected with radioactively labeled bovine serum albumin was fractionated on a Sephadex G-200 column, all the activities described above were reproduced by a fraction containing 7S γ globulin and antigen. The presence in this fraction of a complex of the antigen with mouse immunoglobulin was confirmed by autoradiography. It is quite possible that the alterations in the populations of B- and T-cells described are due to the interactions of such a complex with these cells in the spleen cell suspension.

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This work was supported by a grant from the National Cancer Institute of Canada and Grant MA-3418 from the Medical Research Council of Canada.

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