T1 B cells are found in increased proportions in term cord blood and systemic lupus erythematosus patients. (A) The relative frequency of T1 B cells was determined for term cord blood (n=10), and the peripheral blood of healthy adult donors (n=29) and patients with systemic lupus erythematosus (SLE; n=18). Horizontal bars indicate means. Significant differences using the nonparametric Mann-Whitney U test were detected at P <.01 (^**) and P <.001(^***). (B) A linear regression plot shows that the frequency of B cells with a T1 B-cell phenotype is inversely proportional to the absolute number of peripheral lymphocytes.