Surface expression of costimulatory molecules on KIV, conventional plasmablasts, KSHV⁺EBV⁻ BCP1 cell line, and EBV⁺ LCL. Histograms represent the percentage of CD40⁺, CD70⁺, CD86⁺, CD137L⁺, OX40-L⁺, BAFF-R⁺, ICOS-L⁺, and PD-L1⁺ cells among KIV, conventional plasmablasts, KSHV⁺EBV⁻ BCP1 cell line and EBV⁺ LCL. The number of samples tested for each marker is detailed in the manuscript. ∗P < .05, Mann-Whitney U test.