Plasmacytomagenesis in mice: model of neoplastic development dependent upon chromosomal translocations.

Three model systems of plasmacytomagenesis that are associated with mutations that affect c-myc transcription were discussed. Plasmacytoma induction by chronic peritoneal irritation induced by non-metabolized paraffin oils or plastic objects is strongly influenced by the immune status of the host. BALB/cAn mice must be exposed to natural environmental antigens to develop a high incidence of plasmacytomas. This may be related to T-cell priming. BALB/cAn mice raised under strict SPF conditions are refractory to plasmacytoma induction by pristane. The genotype of the mouse plays an important role in the chronic peritoneal irritation model of plasmacytomagenesis in mice. Only a few of the standard inbred strains are susceptible, notably BALB/cAn and NZB/B1. The genetic basis of susceptibility and resistance has been studied in crosses and congenic strains involving the susceptible BALB/cAn and resistant DBA/2 strains. While several genes play a role in determining resistance at least one resistance gene located on the distal end of Chr 4 reduces the incidence by at least 50% as determined in the BALB/cAn.DBA/2 Fv-1n/n congenic strain. The action of susceptibility and resistance genes is not known; hypothetically these genes could play a role in plasmacytomagenesis by increasing the probabilities of illegitimate exchanges between genes or by influencing the formation of mutations in genes that regulate mitotic cycling. Plasmacytomas appear to develop in the chronic inflammatory tissues induced by these agents. Fundamental unanswered questions are whether these inflammatory tissues provide products such as oxidants in vivo that damage DNA and promote mutagenesis. In the mouse there is a resident self-renewing B cell population that is CD5+. These B cells, which are known to be precursors of normal lamina propria IgA-secreting plasma cells, are directly in contact with the chronic inflammatory process induced by pristane; they may be targets in plasmacytomagenesis. The plasmacytomas that develop by the peritoneal mode of induction all have chromosomal translocations that directly or indirectly activate c-myc. The predominant MACTR found in 90% of these tumors is T(12;15) in which a heavy-chain switch region sequence is joined to the 5' region of c-myc. The evidence strongly suggests that the translocation develops in a late mature B cell that is in the process of isotype switching. An unanswered question is whether the switching associated T(12;15) takes place in a B cell that is exposed to the inflammatory microenvironment.(ABSTRACT TRUNCATED AT 400 WORDS)