*Purpose: Regulatory B cells (Bregs) have shown great potential in cell therapies for murine organ transplantation by inhibiting the proliferation of cytotoxic and helper T cells while promoting the induction of regulatory T cells. However, less is known of their capability to suppress and influence naïve B cell activity. To study this topic, we examined the ability of TLR-Bregs, one type of previously studied Breg expanded in vitro, to suppress naïve B cell proliferation in the presence of LPS stimulation.

*Methods: TLR-Bregs were obtained after purified splenic C57BL/6 B cells were given CpG ODN1668 stimulation for 3 days and LPS (10ug/ml), PMA (50ng/ml), and ionomycin (1ug/ml) stimulation for the last 5 hours. TLR-Bregs and additional naïve B6 B cells were then labelled with Cell Trace Violet and CFSE, respectively. After 5 days of co-culture with LPS, proliferation and markers of activation were measured by flow cytometry.

*Results: In vitro MLR results showed TLR-Bregs directly inhibiting the proliferation of the naïve B cells, when induced by LPS (P < 0.05), in a dose-dependent manner (Fig. A). The presence of TLR-Bregs also resulted in an increase of B cells with the IgM^loIgD^hi mature and CD21+CD23^hi follicular B phenotypes and a decrease in the IgM^hiIgD^lo immature and CD21^hiCD23- marginal B cell phenotypes (P < 0.05, Fig. B-E). Interestingly, TLR-Bregs did not suppress the expression of CD86 but did for CD80 in a dose-dependent manner (P < 0.05, Fig. F, G). While TLR-Bregs showed a slight stimulation to naïve B cells without LPS stimulation, they also showed a much greater suppression of B cells with LPS present.

*Conclusions: TLR-Bregs can suppress the proliferation of naïve B cells induced by LPS. The suppression of CD80 and not CD86 may indicate that the mechanism for which TLR-Bregs suppress other B cells lies in the CD80-relevant pathway.

« Back to 2020 American Transplant Congress