Regulatory role of IgE-binding factors from rat T lymphocytes. II. Glycoprotein nature and source of IgE-potentiating factor

Previous experiments have shown that Fc(ε) receptor-bearing (Fc(ε)R(+)) T lymphocytes in mesenteric lymph nodes (MLN) of rats infected with Nippostronglyus brasiliensis (Nb) release a soluble factor that selectively potentiates the IgE response. The IgE-potentiating factor has affinity for IgE, and can be detected by the ability to inhibit rosette formation of Fc(ε)R(+) cells with IgE-coated erythrocytes. The factor was bound to IgE-coated Sepharose and was eluted from the beads at acid pH. It was also found that the IgE-potentiating factor binds to lentil lectin-Sepharose, indicating that the factor is a glycoprotein. The affinity of the factor for IgE was lost after treatment with trypsin but was maintained after treatment with neuraminidase. However, the ability of the factor to potentiate the IgE response was lost after neuraminidase treatment. The results suggested that the factor's binding site for IgE is associated with a protein (peptide) moiety but that its carbohydrate moiety is essential for its biologic activity. When MLN cells were incubated at 37°C, a substantial amount of the IgE-potentiating factor was released into culture medium within 4 hr even in the presence of cycloheximide. Pretreatment of the cells with trypsin, which removed Fc(ε)R, markedly diminished the release of IgE-potentiating factor, suggesting that the factor is derived from Fc(ε)R on the cell surface.