BALB/c mice have more CD4 + CD25 + T regulatory cells and show greater susceptibility to suppression of their CD4 + CD25 − responder T cells than C57BL/6 mice

Increasing evidence indicates that CD4 + CD25 + T regulatory (Treg) cells control a wide spectrum of immune responses. The initial identification of CD4 + CD25 + Treg cell as a “professional suppressor” was based on observations made in BALB/c mice. This mouse strain is well known to preferentially develop T helper cell type 2 responses, to be more susceptible to intracellular parasite infection, to have a higher tumor incidence, and to be more resistant to the induction of autoimmune diseases, as compared with C57BL/6 (B6) mice. We therefore decided to compare Treg cell function of B6 and BALB/c mice. We observed that the frequency of CD4 + CD25 + T cells in the thymus and peripheral lymphoid organs of BALB/c mice was higher than in B6 mice. CD4 + CD25 + Treg cells from both mouse strains shared similar phenotypic properties, including expression of characteristic immunological markers and hyporesponsiveness to T cell receptor cross‐linking and in their capacity to suppress proliferation of BALB/c CD4 + CD25 − T responder (Tres) cells. However, CD4 + CD25 − Tres cells from B6 mice were notably less susceptible to suppression by CD4 + CD25 + Treg cells from either mouse strain. Our data suggest that the number and the level of suppression of CD4 + CD25 + Treg cells for CD4 + CD25 − Tres cells may be dictated by genetic background. Our data also suggest that differences in the CD4 + CD25 + Treg cell number and the susceptibility of CD4 + CD25 − Tres cells may, at least in part, account for the differences in immune response between B6 and BALB/c strains of mice.