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-5R alpha+ B cells maintained in the presence of IL-5 secreted fewer autoantibodies and had fewer N nucleotides at the 3\u27 end of the D elements compared with CD5- B cells. The reduction in nucleotides, along with the finding that CD5+IL-5R alpha+ 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 VH11 families were expressed with JH1 and the Q52 families were frequently expressed with JH1. Furthermore, JH 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