Summary: Detecting antibodies, particularly those targeting donor human leukocyte antigens in organ transplantation and self-antigens in autoimmune diseases, is crucial for diagnosis and therapy. Radioprotective 105 (RP105), a Toll-like receptor family protein, is expressed in immune-competent cells, such as B cells. Studies in mice have shown that the anti-mouse RP105 antibody strongly activates B cells and triggers an adjuvant effect against viral infections. However, the anti-human RP105 antibody (ɑhRP105) weakly activates human B cells. This study established new culture conditions under, which human B cells are strongly activated by the ɑhRP105. When combined with CpGDNA, specific antibody production against blood group carbohydrates, ɑGal, and SARS-CoV-2 was successfully detected in human B cell cultures. Furthermore, comprehensive analysis using liquid chromatography-electrospray ionization tandem mass spectrometry, single-cell RNA sequencing, and quantitative real-time PCR revealed that ɑhRP105 triggered a different activation stimulus compared to CpGDNA. These findings could help identify antibody-producing B cells in cases of transplant rejection and autoimmune diseases.
