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.