CD27 and type 1 diabetes mellitus: The B cells compartment in children with combined diagnosis had higher percentages of memory B subsets and Bregs, including activated subsets, compared to children with either T1D or C. Children with combined diagnosis had a lower percentage of naive B cells (CD27−CD19+; IgD+CD19+) and an increased percentage of memory B cells (CD27+CD19+; IgD−CD19+).