Serologic and Immunochemical Characterization of an Immunosuppressive Soluble Factor From Mastocytoma-Bearing Mice

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Abstract
Ascitic fluid from mastocytoma-bearing DBA/2 mice depressed the antibody response to sheep red blood cells. Furthermore, cell-free culture fluids from mastocytoma cells grown in vitro were also immunosuppressive. Antisera to the ascitic fluid, as well as those to culture fluids and to extracts, readily neutralized the immunosuppressive activity of the ascitic fluid. Upon immunoelectrophoresis, the absorption of rabbit antisera to ascitic fluid with normal mouse serum resulted in a single precipitin band. This band could be dissociated into two precipitin arcs by digestion with proteolytic enzymes but not with other enzymes. Sephadex G-200 gel filtration at neutral pH indicated that the ascitic fluid could be separated into three peaks, with the first peak containing high-molecular-weight globulins, especially α-globulins, and all the immunosuppressive activity. However, after gel filtration in acidic buffer (pH 3.6), all immunosuppressive activity was present in the third fraction, which contained lower-molecular-weight material. Estimation of molecular weight indicated that the immunosuppressive material, after acid dissociation, was in the range of 5,000 or less, a molecular range similar to that of the dialyzable immunosuppressive material previously found in culture fluids of tumor cells grown in serumfree medium. These results indicated that the immunosuppressive material present in the ascitic fluid of mastocytoma-bearing mice may be a low-molecular-weight peptide that normally complexes with higher-molecular-weight carrier α-globulins.

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