SummaryB7-2–/– non-obese diabetic (NOD) mice develop a spontaneous autoimmune polyneuropathy (SAP) that mimics the progressive form of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). In this study, we focused on the role of regulatory T cells (Tregs) and regulatory B cells (Bregs) in SAP. We found that deletion of B7-2 in female NOD mice led to a lower frequency and number of Tregs and Bregs in spleens and lymph nodes. Tregs but not Bregs suppressed antigen-stimulated splenocyte proliferation, whereas Bregs inhibited the T helper type 1 (Th1) cytokine response. Both Tregs and Bregs induced an increase in CD4+interleukin (IL)−10+ cells, although less effectively in the absence of B7-2. Adoptive transfer studies revealed that Tregs, but not Bregs, suppressed SAP, while Bregs attenuated disease severity when given prior to symptom onset. B cell deficiency in B cell-deficient (muMT)/B7-2–/– NOD mice prevented the development of SAP, which would indicate that the pathogenic role of B cells predominates over its regulatory role in this model. We conclude that Bregs and Tregs control the immunopathogenesis and progression of SAP in a non-redundant fashion, and that therapies aimed at expansion of Bregs and Tregs may be an effective approach in autoimmune neuropathies.