iNKT cells defects in patients with HHV-8 MCD are associated with a profound decrease in circulating and splenic MZ B cells. PBMCs and SMCs from controls (HDs and patients with KS) or patients with HHV-8 MCD were surface stained with CD19, CD27, IgD, IgM, CD21, CD23, CD1d, and CD1c to identify B-cell subsets. (A) Representative flow cytometry plot showing surface expression of CD27 and IgD on CD19⁺ B cells from blood samples of HDs, patients with KS, and patients with HHV-8 MCD. Bar chart showing frequencies of naïve (CD27⁻ IgD⁺ IgM⁺), switched memory (CD27⁺ IgD⁻ IgM⁻), MZ (CD27⁺ IgD^low IgM⁺ CD21^hi CD23⁻ CD1c^hi), CD27⁻ memory (CD27⁻ IgD⁻ IgM⁻), and IgM only (CD27⁺ IgD⁻ IgM⁺) CD19⁺ B cells in 22 HDs, 18 patients with KS, and 17 patients with HHV-8 MCD. Bar chart shows cumulative data as frequencies and median ± ranges. Significant P < .05, Kruskal-Wallis and Mann-Whitney tests. (B) Representative flow cytometry plot showing surface expression of CD27 and IgD on CD19⁺ B cells from spleen samples from HDs and patients with HHV-8 MCD. Bar chart showing frequencies of naïve, switched memory, MZ, CD27⁻ memory, and IgM only CD19⁺ B cells as defined in PBMCs from 6 HDs and 4 patients with HHV-8 MCD. Bar chart shows cumulative data as frequencies and median ± ranges. Significant P < .05, Mann-Whitney tests. (C) Correlation plots show the relationship between frequencies of iNKT with MZ B cells (CD27⁺ IgD⁺) or switched memory B cells (CD27⁺ IgD⁻) in the PBMCs of HDs, patients with KS, and patients with HHV-8 MCD. Spearman’s correlation test.