Chen, Lili

MHC Class II molecules are essential in antigen presentation and selection of the CD4+ T cell repertoire. They are mainly expressed on professional Antigen Presenting Cells (APC), i.e. B lymphocytes, dendritic cells and macrophages. Activated human T lymphocytes also express MHC Class II but MHC Class II expression is not detected on activated mouse T cells. HLA‐DR3 can be expressed as a transgene on CD4+ T cells in complete MHC Class II knock‐out (AEo) mice, but not in I‐Ab knock‐out (Abo) mice, suggesting that a gene, which could modify the expression of HLA‐DR3, might exist between I‐A and I‐E. Expression sequence tag (EST) databases were searched using the flank regions between I‐A and I‐E and a new potential gene was identified. No similar sequence was found in the human genome database. Expression in multiple mouse tissues, but not in human cell lines, was verified by RT‐PCR. However, this gene was found to be expressed in B6 mouse B cells and two mouse B cell lines, but not in T cells, indicating that it might not be related to the expression of HLA‐DR3. Transduction of this gene into the LG2 cell line had no effect on MHC II expression. In summary, we report the discovery of a new gene between the I‐Aa and I‐Eb1 region in C57BL/6 mice and its function remains unknown. (Supported by NIH‐AI30554)

Signaling by the B cell–activating receptor TACI drives T cell–independent IgA responses to gut commensal bacteria.