The effects of fractions (Chalones) obtained from lymphoid organs on lymphocyte proliferation in vitro

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Abstract
Aqueous extracts of lymphoid organs were prepared and fractionated by means of gel filtration, ion exchange chromatography, and isoelectric focusing. A protein-containing fraction with a molecular weight of approximately 80,000–90,000 and isoelectric points of 7.6 and 5.3–6.2 was isolated and shown to inhibit reproducibly both thymidine incorporation and proliferation of concanavalin A-stimulated mouse spleen lymphocytes in vitro. This effect appeared specific, since proliferation of mastocytoma P-815 and leukemia L-1210 cells remained unaffected. A small molecular weight fraction (500 to 10,000 daltons) was also found to inhibit lymphocyte proliferation in vitro but was without apparent specificity for cell type.