Putative bovine B cell lineage tumor in sporadic bovine leukosis

Two calves (C924 and C928) clinically identified as suffering from the calf type of sporadic bovine leukosis (SBL) were examined for immunophenotypical distribution of their peripheral blood lymphocytes (PBL) with T cell or B cell specific monoclonal antibodies (mAbs). Flow cytometric profile analysis indicated that both calves possessed a high population of MHC class II positive cells and a low population carrying T cell associated markers. More than 93% of the PBL of C928 were positive for MHC class II and BoCD5, but were not IgM positive, indicating that clonal tumor cells (MHC-II+, BoCD5+ and IgM-) accounted for most of the PBL of C928. A tumor cell line, BLC3, established from calf C924 in nude mice was examined for immunophenotype, DNA rearrangement of immunoglobulin (Ig) genes and expression of cellular oncogenes c-abl, c-myc and c-myb. BLC3 showed a characteristic profile, being MHC class I and MHC class II positive, but without T cell associated markers. Although the rearranged configuration in the Ig loci was not clearly found in Southern blot analysis using sheep Ig probes, steady-state levels of c-myb transcripts were detected in tumor cell line BLC3 by Northern blot hybridization. Taken together, our data show that the calf type of SBL found in these two calves is induced by immature pre-B cells, including tumor cell line BLC3 established in nude mice.