The present invention relates to a distinct B cell subset, B10 cells, that regulate T cell mediated inflammatory responses through the secretion of interleukin-10 (IL-10). The invention also relates to the use of B10 cells in the manipulation of immune and inflammatory responses, and in the treatment of disease. Therapeutic approaches involving adoptive transfer of B10 cells, or expansion of their endogenous levels for controlling autoimmune or inflammatory diseases and conditions are described. Ablation of B10 cells, or inhibition of their IL-10 production can be used to upregulate immunodeficient conditions, ameliorate infectious diseases and/or to treat tumors/cancer. Diagnostic applications are also encompassed.
