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-2 k (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-2 k (AKR and C3H/He) mice. The phenotype of the PBMCs in which Q5 transcription takes place seems to be, at least partly, CD3 - 4 - 8 - cells that might be related to CD3 - 4 - 8 - spontaneous thymoma cells derived from an H-2 k mouse. Conclusion: The expression of Q5 in tumor cells in general is a result of a change of transcriptional regulation associated with malignant transformation.