Maintenance of CD5 + B Cells at an Early Developmental Stage by Interleukin-5: Evidence from Immunoglobulin Gene Usage in Interleukin-5 Transgenic Mice

We have characterized the development and expansion of CD5⁺ B cells in interleukin-5 (IL-5) transgenic mice in terms of autoantibody production and immunoglobulin gene usage. CD5⁺IL-5Rα⁺ B cells maintained in the presence of IL-5 secreted fewer autoantibodies and had fewer N nucleotides at the 3′ end of the D elements compared with CD5⁻ B cells. The reduction in nucleotides, along with the finding that CD5⁺IL-5Rα⁺ B cells in IL-5 transgenic mice use Q52 families more frequently than age-matched control B cells, also suggests that these cells have the characteristics of fetus-type B cells and represent an early stage of B-cell development. All of the V_H11 families were expressed with J_H1 and the Q52 families were frequently expressed with J_H1. Furthermore, J_H proximal DQ52 was frequently used in IL-5 transgenic mice. All of these characteristics in terms of immunoglobulin gene usage have been described for CD5⁺ B cells. These results suggest that IL-5 maintains CD5⁺ B cells that have a fetus-type of immunoglobulin gene usage. This cytokine could be responsible for prolonging the life span of immature CD5⁺ B cells, which subsequently mature to CD5⁻ B cells that secrete polyreactive natural antibodies.