To determine whether old B cells have the same capacity to switch isotypes as young cells, we purified splenic follicular, marginal zone, and age-associated B cell subsets from C57BL/6 mice. Cells were stimulated in culture with interleukin 4 and either lipopolysaccharide or anti-CD40, and switching to IgG1 was measured by flow cytometry of surface immunoglobulin. The results show that switching was robust in follicular and marginal zone B cells from old mice and was comparable to their young counterparts. However, age-associated B cells from old mice switched poorly relative to the other subsets. Expression of activation-induced deaminase, which initiates switching, was quantified by qPCR of mRNA, and it was equal between young and old follicular B cells. Thus, in this ex vivo system, the follicular and marginal zone cells from young and old mice behaved similarly, showing that the molecular machinery to perform switching is intact in old B cells. The adaptive immune response has been linked to cardiovascular disease, suggesting that potential immune intervention strategies could reduce disease severity and prolong life. To achieve this goal, we have focused on understanding the role of B cells in atherosclerosis. We are testing the role of antibody isotype using a novel mouse model, and we are characterizing the antibodies produced by mouse aortic B cells. We are also determining what antigens they bind and how antibodies can promote disease.
