Mycoplasma‐induced degradation of IgE bound by Fcϵ receptors of rat basophilic leukemia cells

Previous studies from this laboratory have shown that Mycoplasma hyorhinis interacts with some unoccupied, high-affinity 45-kDa receptors for IgE on rat basophilic leukemia (RBL) cells to induce the formation of 71-kDa receptors for IgE. The present study demonstrates that when IgE is bound to the high-affinity receptors, exposure of RBL cells to mycoplasma leads to a time-dependent degradation of the cell-bound IgE into fragments of 186 kDa, 158 kDa and 115 kDa, all of which remain bound to the receptors. Upon reduction, these fragments yield 67-kDa and 55-kDa epsilon chain-derived polypeptides. The degradation appears to start at the N-terminus of the IgE, leading eventually to a complete loss of L chains. In the absence of mycoplasma, the IgE remains relatively intact throughout the same time period with a molecular mass of 210 kDa. The observed degradation of receptor-bound IgE by mycoplasma, should it also occur in vivo, could have important consequences as far as the IgE-dependent mediator release is concerned.