EXPRESSION OF A MOUSE CHANNEL CATFISH CHIMERIC IGM MOLECULE IN A MOUSE MYELOMA CELL

Fusion genes encoding a murine V(H) domain and the constant region dom ains of the mu chain from the channel catfish, Ictalurus punctatus, we re stably expressed in the lambda light chain producing mouse myeloma cell line J558L. Although the pathways of pre-mRNA processing for expr ession of membrane (mum) and secreted (mus) forms of the mu chain diff er between mammals and teleosts, mRNAs encoding both catfish mum and m us were correctly expressed in the mouse myeloma cells. The mouse-chan nel catfish chimeric mu chain polypeptide was able to associate covale ntly with the mouse lambda light chain and assemble, intracellularly, into polymers of covalent structure (muL)2-8 which resembled those see n with native catfish IgM. In contrast to native catfish IgM, the mous e-catfish chimeric IgM showed the property of binding strongly to prot ein A of Staphylococcus aureus. The mouse-channel catfish chimeric IgM was core-glycosylated, but did not contain terminal sialic acid. Secr etion rates for the chimeric IgM were low, and the possibility could n ot be excluded that extracellular chimeric IgM was released from dead or dying cells. The reason(s) for the intracellular retention of the c himeric IgM (probably in the endoplasmic reticulum) are not known, but those mechanisms involving retention via cysteine residues were exclu ded.