Effect of age, sex, race, and body mass index (BMI) on distribution of MBCs. Splenocytes, blood, BM, or intestinal tissue cells were stained as in Figure 1. (A) The frequencies of CD19⁺ CD27⁺ MBCs in these samples were correlated with age. Using the unpaired one-way analysis of variance with Tukey’s correction or the unpaired two-tailed Student t test analysis with Welch’s correction, no significant difference was found for spleen (P = .65), blood (P = .53), or BM (P = .86). For donors aged 18 to 49 years, there was a significant difference (*P = .036) in the gut compared with older donors. (B) Correlation of frequencies of CD19⁺ CD27⁺ MBCs with sex. (C) Correlation of frequencies of CD19⁺ CD27⁺ MBCs with race. The blood of white donors had significantly more MBCs than the blood of Hispanic donors (*P = .0391). (D) The resulting ratio of CD19⁺ CD27⁺ (memory) to CD19⁺ CD27^– (naive) B cells in spleen was further correlated with the BMI of the donors analyzed. Significance was tested by linear regression (slope, −0.06; R² = 0.047;P = .23, ns).