T regulatory cell levels in transferred mice. The percentages of CD4⁺CD25^hi+FoxP3⁺ Tregs in the (A) spleens and (C) thymuses of irradiated SCID mice engrafted with 1.5 × 10⁴ splenocytes from CD61 KO mice immunized against BALB/c platelets (N = 10, open columns). The percentages of Tregs in organs from irradiated SCID mice engrafted with 1.5 × 10⁴ splenocytes from CD61 KO mice immunized against BALB/c platelets and treated biweekly with 2 g/kg IVIg (N = 10, black columns) are shown for comparison. Data are expressed as the percent CD4⁺CD25^hi+ T cells (± SEM) in the fluorescence gates, as shown in Figure 2. The solid horizontal line in the panels represents the normal mean percentage (± SEM hatched lines) of CD4⁺CD25^hi+FoxP3⁺ Tregs in aged-matched BALB/c mice (N = 10). (A,C) *P < .05, **P < .01, statistical significance between the ITP mice (open columns) and IVIg-treated mice (black columns). (B,D) The proportional data were adjusted for differences in splenic and thymic mass, respectively, to reflect the total lymphocyte content of these organs.