(A) Splenic lymphocytes were isolated from age and gender-matched SPF, germ-free (GF) and RF mice, and stained to delineate MZ B cells (CD19, CD21, IgM and IgD). The percentages of cell populations with MZ B cell phenotypes are indicated. Data represents at least three independent experiments, and two different strains (C57/BL6 and Swiss Webster) of germ-free mice. (B–D) Tabulation of data from individual age-matched mice (8–10 weeks) reared in SPF, GF, or RF conditions: (B) Percentage of CD19+ B cells; (C) % MZ B cells; (D) total MZ B cells per spleen. P values were calculated using student’s t test comparison of GF or RF to the control SPF group.