Phenotype of circulating IgM⁺λ⁺CD38^high cells during KSHV-MCD flare. (A) P1 PBMCs were isolated using Ficoll gradient and stained using the method described in “Material and Methods.” At least 10⁶ events were acquired. Gating strategy was performed as follows: (1) gating on single cells; (2) exclusion of T cells (CD3⁺) and monocytes (CD14⁺); (3) gating on IgM⁺CD38^high cells; (4) gating on λ⁺ cells; and (5) assessment of CD19, CD20, CD24, CD27, and CD40 expression. Retrogating of the IgM⁺λ⁺CD38^high population was performed on a side scatter/forward scatter (SSC/FSC) dot plot. Positivity threshold was determined on the fluorochrome corresponding isotype (depicted in blue). P1 is shown as a representative example. (B) Percentage of CD19, CD20, CD24, and CD27 positivity among IgM⁺λ⁺CD38^high circulating cells detected in 14 patients with KSHV-MCD.