CD19 and type 1 diabetes mellitus: Reported perturbations among B cell subsets in type 1 diabetes include increased frequencies of transitional (CD27−IgD+IgM−) B cells [8], increased frequencies of marginal zone (CD19+CD21+CD23−) B cells and decreased frequencies of follicular (CD19+CD21−CD23+) and regulatory (CD1d+CD5+CD19+) B cells [9].