Murine B cell hybridomas bearing ligand-inducible Fc receptors for IgE.

Interest in the regulation of IgE synthesis has generated investigation of low-affinity Fc receptors for IgE (Fc epsilon R) and the related immunoregulatory IgE-binding factors. In an effort to facilitate biochemical analysis of the B lymphocyte Fc epsilon R, hybridoma technology has been used to create stable cell lines that maintain Fc epsilon R in high numbers. Fusion of the HAT-sensitive B lymphoma, M12.4.5, with murine B cells from Nippostrongylus brasiliensis infected BALB/c mice led to the formation of hybrid cells of B cell phenotype, all of which were Fc epsilon R+, including several that had greater than 50,000 Fc epsilon R/cell. The Fc epsilon R on these cells were biochemically identical to the Fc epsilon R on normal B cells with respect to binding affinity (approximately equal to 10(8) M-1), m.w. (49,000), and tryptic peptides. Each hybridoma cell line specifically increased its Fc epsilon R level between twofold and fourfold when cultured with rat or mouse IgE. Additional studies demonstrated that the increased IgE binding ability was due to an increase in receptor number rather than an affinity change, and the Fc epsilon R increase was seen on the entire cell population. Dose studies indicated that oligomeric IgE was 10-fold more effective than monomeric IgE in causing upregulation, and the effective concentrations required indicated that induction occurred only if IgE was present in saturating concentrations. Upon addition of IgE, peak Fc epsilon R levels were reached after 15 to 20 hr of culture; blocking protein synthesis with cycloheximide largely blocked the increase in Fc epsilon R levels. Additionally, the inductive signal IgE must constantly be present to maintain upregulated Fc epsilon R levels in that its removal from the culture resulted in a rapid decline of Fc epsilon R from induced to normal levels. Because Fc receptor upregulation is important to several systems describing Ig isotype-specific regulation, the ability to examine such receptor upregulation at a clonal level should aid in discerning the role of the Fc epsilon R in the regulation of IgE antibody synthesis.