Lymphoid Tumors ofXenopus laeviswith Different Capacities for Growth in Larvae and Adults

摘要

Three new lymphoid tumors offering an assortment of variants in terms of MHC class Iexpressions, MHC class II expression, and Ig gene transcription have been discovered in theamphibianXenopus. One was developed in an individual of the isogenic LG15 clone(LG15/0), one in a frog of the LG15/40 clone (derived from a small egg recombinant ofLG15), and one (ff-2) in a maleffsib of the individual in which MAR1, the first lymphoidtumor in Xenopus was found 2 years ago. These tumors developed primarily as thymusoutgrowths and were transplantable in histocompatible tadpoles but not in nonhistocompatiblehosts. Whereas LG15/0 and LG15/40 tumor cells also grow in adult LG15 frogs, theff-2 tumor, like the MAR1 cell line, is rejected by adultffanimals. Using flow cytometry withfluorescence-labeled antibodies and immunoprecipitation analysis, we could demonstratethat, like MAR1, these three new tumors express on their cell surface lymphopoieticmarkers recognized by mAbs FIF6 and RC47, as well as T-cell lineage markers recognizedby mAbs AM22 (CD8-1ike) and X21.2, but not by immunologobulin (Ig) nor MHC class IImolecules. Another lymphocyte-specific marker AM15 is expressed by 15/0 and 15/40 butnotff-2 tumor cells. Theff-2 tumor cell expresses MHC class molecule in association withβ2-microglobulin on the surface, 15/40 cells contain cytoplasmic Iαchain that isbarely detected at the cell surface by fluocytometry, and 15/0 cells do not synthesize classIαchain at all. The three new tumors all produce large amounts of IgM mRNA of twodifferent sizes but no Ig protein on the membrane nor in the cytoplasm. All tumor cell typessynthesize large amount of Myc mRNA and MHC class I-like transcripts considered to benon classical.