mature B cell regulatory B cell Regulatory B cells reportedly represent 1-2% of the spleen and 7-8% of the peritoneal B220-positive cells in mice. They are also found in the bone marrow, lymph node, and blood of mice. These cells are also reportedly capable of secreting IL-10 and are reportedly CD5-positive, CD21-positive, CD24-positive, CD93-negative, B220-positive, IgM-positive, and IgD-positive. Breg A mature B cell that has the phenotype CD1d-positive and expresses interleukin-10. This cell type has been associated with suppression of chronic inflammatory responses and T cell responses. B(reg) regulatory B-lymphocyte regulatory B-cell regulatory B lymphocyte NCIt:C113502 B10 cell