Immunoglobulin binding factor (IBF) produced by T cells: selective interaction with slow migrating rabbit IgC.

Antigen-stimulated T lymphocytes release a variety of soluble factors among which an Immunoglobulin Binding Factor (IBF). We report a method of titration of IBF making use of its capacity to inhibit complement-dependent hemolysis of sheep erythrocytes sensitized with rabbit IgG antibodies. Using this technique we have investigated the specificity of IBG for rabbit immunoglobulins fractionated by DEAE-cellulose chromatography. The interaction of IBF with IgG is found to be restricted to the slowest migrating fractions of rabbit IgG.