Background/Purpose:

Autoantibodies – secreted by short- and long-lived plasma cells in bone marrow and spleen – trigger the immune response, and immune complex deposits in the kidneys can lead to the development of a severe nephritis. As such, autoreactive plasma cells contribute to the pathogenesis of the autoimmune disease Systemic Lupus Erythematosus (SLE). In NZB/W mice – a mouse model for SLE – both parental strains New Zealand Black (NZB) and New Zealand White (NZW) add different sle-loci to the formation of SLE. The NZB strain passes the sle2c locus that contains the gene for the Thrombopoietin (TPO)-receptor (c-mpl). According to the relevance of megakaryocytes for the plasma cell niche and the correlation between plasma cell and megakaryocyte numbers, we wanted to elucidate whether megakaryopoiesis, c-Mpl or c-Mpl signaling is altered in autoimmune mice.

Methods:

We assessed the amount, and cellular environment of megakaryocytes and plasma cells in spleen and bone marrow of wildtype, NZB, NZW and NZB/W mice via flow-cytometry and confocal microscopy. We also investigated the intensity of megakaryopoiesis upon TPO stimulation, the occurrence of genetic variations for c-mpl and the activation of signaling pathways downstream of c-Mpl by in vitro studies, and by gene and protein analysis.

Results:

We found the 10-fold amount of long-lived plasma cells and megakaryocytes in the spleens of NZB mice compared to wildtype, in NZW mice equal numbers, and in NZB/W mice numbers between those for NZB and NZW or wildtype. Furthermore, in the spleen a fraction of plasma cells clustered around megakaryocytes and in vitro megakaryocytes support plasma cell survival. Upon TPO stimulation of splenocyte and bone marrow cultures, NZB megakaryocytes proliferated significantly stronger resulting in the double amount of megakaryocytes compared to NZW cultures. Via sequence analysis we detected a missense mutation in the c-mpl gene of NZB mice leading to an amino acid replacement within the essential TPO-binding site. However, in vitro experiments with wildtype and mutant c-mpl BaF3-clones revealed that this mutation is actually hampering the proliferation upon TPO stimulation and hyperactivation of downstream signals is overcompensating.

Conclusion:

In summary, our data indicate that augmented megakaryopoiesis enables the accumulation of a greater number of autoreactive plasma cells in lupus prone NZB/W mice. Thus, we propose that enhanced megakaryopoiesis and greater megakaryocyte numbers are contributing to the development and/or pathogenesis of SLE.

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« Back to 2013 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/augmented-megakaryopoiesis-supports-accumulation-of-plasma-cells-in-lupus-prone-mice/