Mouse immunoglobulin e chain gene was cloned from DNA of a hybridoma producing anti-dinitrophenyl IgE, which was constructed by fusing a spleen cell of a BALB/c mouse with a variant clone of MOPC21 myeloma (IgGI producer Immunoglobulin heavy chain (H) genes consist of a family of variable region (V) genes and several constant region (C) genes which, in the mouse, are classified into five major classes, ji, y, a, 8, and E. In the early phase of B-lymphocyte differentiation, a given V sequence is first expressed as a A chain and, subsequently, the same V sequence is associated with other classes of CH sequences. The phenomenon is called H chain class switch. Based on comparative studies on the rearranged and germ-line H genes (1, 2), we have proposed a model that explains H chain class switch by at least two types of recombination events to construct a complete H gene. The first type of recombination takes place between a given VH, a D, and a JH gene segment and forms a complete V gene associated with the C, gene (3-5). The same V gene is subsequently associated with other classes of CH genes by the second type of recombination which takes place between S regions located in the 5' side of each CH gene.Results supporting this model were also reported from other laboratories (3,4,6,7). Inasmuch as the active CH gene is expected to contain a J gene and a portion of the S region in the 5' side of the CM, gene (SM) between the V and CH genes according to this model, it is possible to isolate directly any expressed genomic CH genes, by using theJ or S, DNA segments as probes, from DNAs of myelomas or cell lines that are actively producing particular heavy chains.Recent studies using cloned DNA segments have revealed basic structure of mouse CH gene loci (8-11). We have proposed the order of mouse CH genes as 5'-A-y3-y1-

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IgE anti-DNP antibody-secreting hybridomas were obtained by polyethylene glycol fusion of murine myeloma cells with spleen cells from mice, primed with DNP-KLH and challenged with DNP-Nippostrongylus brasiliensis extract. The in vivo and in vitro continuously growing hybridomas are producing high amounts of monoclonal IgE anti-DNP antibodies, which are heat-labile, hapten-specific and have rat mast cell sensitizing capacity.

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