TLR‐mediated stimulation of APC: Distinct cytokine responses of B cells and dendritic cells

Abstract

In addition to their role in humoral immunity, B lymphocytes are important antigen‐presenting cells (APC). In the same way as other APC, B cells make cytokines upon activation and have the potential to modulate T cell responses. In this study, we investigated which mouse B cell subsets are the most potent cytokine producers, and examined the role of Toll‐like receptors (TLR) in the control of secretion of IL‐6, IL‐10, IL‐12 and IFN‐γ by B cells. Production of some cytokines was restricted to particular subsets. Marginal zone and B1 cells were the predominant source of B cell IL‐10 in the spleen. Conversely, follicular B cells were found to express IFN‐γ mRNA directly ex vivo. The nature of the activating stimulus dramatically influenced the cytokine made by B cells. Thus, in response to combined TLR stimulation, or via phorbol esters, IFN‐γ was secreted. IL‐10 was elicited by T‐dependent activation or stimulation through TLR2, 4 or 9. This pattern of cytokine expression contrasts with that elicited from dendritic cells. QRT‐PCR array data indicate that this may be due to differential expression of TLR signalling molecules, effectors and adaptors. Our data highlight the potentially unique nature of immune modulation when B cells act as APC.