PTPN22 and type 1 diabetes mellitus: In the present study, we employed a comprehensive flow cytometry approach, using 15 fluorochrome-conjugated surface markers, to characterize the B cell compartment in the peripheral blood of T1D patients and healthy individuals, and assessed the role of six T1D loci implicated in B cell function, including the PTPN22 Trp620 non-synonymous allele, in the regulation of this immune compartment.