CTLA4 and systemic lupus erythematosus: It has been further shown in a murine SLE model that following treatment with CTLA4-Ig (Abatacept), a recombinant fusion protein that contains the Fc fragment of human IgG1 and binds either to CD80 or CD86 with a much higher avidity than CD28, that there is a reduction in both numbers of autoreactive B cells and autoantibodies [56].