Tumor cell-specific transcription of a murine histocompatibility class Ib Q5 gene.

BACKGROUND We previously reported that the Q5 gene product (Q5 antigen) was expressed on the surface of various tumor cells derived from H-2k (Qa-2-) mice. The Q5 antigen has tumor-protective antigenicity in the syngeneic mice. MATERIALS AND METHODS Transcripts of the Qa region genes were analyzed by the RT-PCR method. Cell fractionation was performed with the MACS method and the phenotypes were estimated by flow cytometry analysis. RESULTS Transcripts of Q5 were produced by all tumor cell lines. The Q5 transcription was detected only in thymocytes and PBMCs of H-2k (AKR and C3H/He) mice. The phenotype of the PBMCs in which Q5 transcription takes place seems to be, at least partly, CD3-48 cells that might be related to CD3-4-8- spontaneous thymoma cells derived from an H-2k mouse. CONCLUSION The expression of Q5 in tumor cells in general is a result of a change of transcriptional regulation associated with malignant transformation.