Regulation of autoreactive B cells in the non-autoimmune R4A -IgG2b transgenic mouse model, and, The role of estrogen in the immune system regulation

Abstract

Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterized by the presence of high titers of anti-double-stranded (ds) DNA antibodies in the serum of SLE patients and in SLE-prone mice strains; and has been attributed to defects in B and or T cell regulation. The incidence of SLE is higher among females than males (ratio 10:1). Several lines of evidence implicate estrogen in the development of autoantibodies and in exacerbation of murine models of SLE. Androgens, anti-estrogens and ovariectomy have reciprocally been implicated in amelioration of SLE-like disease in mice.;To understand the defects in SLE and to determine mechanisms of B cell regulation, we used in this study, a non-autoimmune mouse model that is transgenic for an anti-dsDNA antibody R4A, and has negligible anti-dsDNA activity in its serum. This study involved two approaches, (1) to determine if a clonally indifferent B cell population exists in this mouse model, and to determine its molecular characteristics: and to define the populations of anti-DNA B cells in these mice, (2) to elucidate the effect of estrogen on the expression of anti-dsDNA antibodies and to begin to elucidate mechanisms of estrogen-induced dysregulation. We obtained non-tolerized, low affinity anti-DNA antibody secreting B cells from these mice by fusion. These antibodies displayed apparent affinities 1 to 4 logs lower than affinities of the deleted or anergic high affinity B cells and differ by only a few amino acids from the high affinity antibodies; and unlike the high a affinity B cells pathogenic. We administered estrogen, to these mice to determine the effects of estrogen on autoantibody expression. Sera obtained from estrogen and placebo treated mice show significant rise in anti-dsDNA titers in estrogen treated mice over placebo. High affinity anti-DNA antibody-secreting B cells were obtained from estrogen treated mice by fusion; and ELIspot analysis show significantly more high affinity anti-DNA B cells in estrogen treated mice compared to mice treated with placebo. In addition, immunohistochemistry analysis of spleens from estrogen and placebo treated mice show increased expression in estrogen treated mice compared to mice treated with placebo. The results of this study suggests that, (1) the clonally indifferent low affinity B cell population can mutate to become high affinity pathogenic B cells and suggest a possible route to autoimmune diseases, (2) estrogen plays a role in the rescue autoreactive B cells in the bone marrow and spleen and upregulates B cell proliferation in estradiol treated mice, (3) estrogen may be effecting multiple pathways that lead to B cell expansion, activation and immunoglobulin production.