Lymphocyte subsets and B cell signatures in lupus nephritis : impact on disease relapse and effect of immunosuppressive medications

Abstract

Repeated renal relapses portend adverse clinical outcomes and increased risk of kidney failure in patients with lupus nephritis (LN). The mechanisms leading to LN relapses are poorly understood, and prediction remains difficult. Prevention of relapses is by empirical long-term immunosuppressive treatment. In this regard, mycophenolate is associated with a lower relapse rate than azathioprine. Aberrations in lymphocyte subsets, especially the B cell repertoire, have been implicated in LN relapse. miRNA-148a, BACH1, BACH2 and PAX5 are B cell signatures which play important regulatory roles in B cell homeostasis, but their pathogenic relevance in LN relapses, and also the effect of mycophenolate and azathioprine, have not been investigated. This project investigated B lymphocyte subsets and cellular signatures in LN patients, and compared patients with multiple relapses (MR, ≥3 relapses within 36 months, n=19) against those with no relapse (NR, n=14). The percentage of circulating naïve B cells was lower in MR patients, who also showed a higher memory-to-naïve B cell ratio, than the NR group. MR patients showed higher blood levels and increased intracellular expression of miRNA-148a, and lower BACH1, BACH2 and PAX5 expression in naïve and memory B cells compared with NR. Circulating T cell subsets and related serum cytokine profiles were not different between the two groups. Circulating B lymphocytes were isolated from five treatment-naïve active LN patients, and in vitro antagomir-148a treatment resulted in upregulation of BACH1, BACH2 and PAX5 expression, and reduced B cell proliferation upon stimulation. Treatment of B lymphocytes with mycophenolate in vitro resulted in reduced miRNA-148a and increased BACH1, BACH2 and PAX5 expression, and reduced proliferation upon stimulation, compared with azathioprine. B lymphocytes isolated from ten clinically stable LN patients receiving mycophenolate treatment also showed lower miRNA-148a and higher BACH1, BACH2 and PAX5 expression, and decreased proliferation upon ex vivo stimulation, when compared to B cells from nine patients receiving azathioprine. Overall these findings provide evidence that LN relapse is associated with altered B cell subsets and cellular signature. Also, data from in vitro and ex vivo studies show that mycophenolate treatment is associated with a distinct cellular signature which is in turn associated with a lower relapse rate.