Regulation of Homocytotropic Antibody Formation in the Rat

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Abstract
Chemical and physicochemical properties of the previously reported “antigen-specific T cell factor” that negatively regulates hapten-specific homocytotropic antibody (HTA) response in the rat were investigated. This factor, which is extractable from mechanically disrupted thymocytes obtained from rats hyperimmunized with dinitrophenylated Ascaris suum extract (DNP-As), showed a strong inhibitory effect on hapten-specific HTA formation in recipient animals that had been x-irradiated and immunized with DNP-As so as to produce high and persistent HTA formation. The treatment of the thymocyte extract with proteinases and nucleases revealed that the active factor is not digestible by DNase and RNase, but is destroyable by trypsin and Pronase, indicating the protein nature of the T cell factor. In sucrose density gradient ultracentrifugation, the activity sedimented slower than IgG hemagglutinin. In gel filtration with Sephadex G-100, the inhibitory activity was not detected in the fraction eluted with a void volume, but was found in a fraction eluted in the range between about 35,000 and 60,000 daltons. By electrophoresis in agar the activity was located in regions corresponding to rat α- and β-globulins but not in regions corresponding to albumin and γ-globulin. These results indicate that the antigen-specific inhibitory T cell factor is a protein with a smaller molecular weight than other immunoglobulins, further supporting previous findings that the T cell factor is not a usual immunoglobulin but may be a unique receptor of T cells.

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