Louvain Rat Immunocytomas

This chapter introduces a Louvain rat model of immunoglobulin-secreting tumors, which is a valuable tool in immunology. The model has provided many new possibilities for experimental research, such as monoclonal immunoglobulins of eight different classes or subclasses from a highly utilized laboratory animal species, and especially the first immunoglobulin (IgE) and IgD monoclonal immunoglobulins identified in an animal species. The chapter discusses the development of a rat–rat hybridoma technology which has many features distinctive from the mouse model, at least in its antibody repertoire. Etiological factors which can influence this tumor incidence and also mechanisms of cell transformation at the level of chromosomal constitution of the IR tumor are presented. The cytogenetic and molecular studies of the IR tumors or rat immunocytomas (RIC) show that in three different tumors (BL, MPC, and RIC) in three different species (human, mouse, and rat), nearly identical genetic loci (c-myc, Ig) are juxtaposed via chromosomal translocation. These three tumors represent at least two different stages of B-cell maturation, and the natural histories and modes of induction of the tumors are very different. The finding that c-myc-Ig juxtaposition occurs in these three tumors suggests that this configuration plays a central role in the genesis of the B-cell tumors. The findings also indicate that sequences, in addition to Ig-switch sequences, may serve as translocation targets. The involvement of a LINE region in the IR209 raises the possibility that c-myc activation can occur without interposition into Ig-influenced chromatin.