BACKGROUND: CpG oligonucleotide has been shown to strengthen the function of peripheral blood mononuclear cells (PBMCs), but its effects on type 1 diabetes mellitus has been rarely reported. OBJECTIVE: To investigate the effects of CpG oligonucleotide on the expression of interferon γ (IFN-γ), interleukin (IL) -12 and IL-10 in PBMCs in patients with type 1 diabetes mellitus versus healthy controls. METHODS: PBMCs were isolated from patients with type 1 diabetes mellitus and healthy controls and then cultured in RPMI-1640 with non-stimulator (control group) and CpG oligonucleotide (CpG oligonucleotide group), respectively. The mRNA expression of IFN-γ, IL-10, and IL-12 in PBMCs was detected by reverse transcription-polymerase chain reaction. RESULTS AND CONCLUSION: mRNA expression of IFN-γ and IL-10 was significantly lower in patients with type 1 diametes mellitus than in healthy controls (P < 0.01). In the CpG oligonucleotide group, the mRNA expression of IFN-γand IL-12 was significantly higher than in the healthy control group (P < 0.01), but the mRNA expression of IL-10 was similar to that in the healthy control group (P > 0.05). These findings demonstrated that CpG oligonucleotide can promote the production of IFN-γ and IL-12 in PBMCs of type 1 diametes mellitus.