FRI0376 Mechanism of Phenotype Conversion from Rheumatoid Arthritis to Lupus in FCᴦRIIB-Deficient C57BL/6 YAA Mice
Authors: S. Kawano, H. Amano, Q. Lin, K. Nishikawa, H.T. Tsurui, T. Shirai, S. Hirose, Y. Takasaki
Journal: Annals of the Rheumatic Diseases (2015)

<h3>Background</h3> We previously obtained a FcγRIIB-deficient C57BL/6 (B6) congenic strain of mice, which spontaneously developed severe rheumatoid arthritis (RA). The introduction of the <i>Yaa</i> (<i>Y-linked autoimmune acceleration</i>) mutation, which is a consequence of a translocation from the telomeric end of the X chromosome containing the <i>Tlr7</i> gene onto the Y chromosome, to the FcγRIIB-deficient B6 (B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i>) mice developed lupus like nephritis but not RA. This phenotype conversion did not depend on autoantibody specificity, since the mice showed a marked increase in serum levels of both lupus-related and RA related autoantibodies. <h3>Objectives</h3> To examine the mechanism of the disease phenotype conversion from RA (B6.FcγRIIB<sup>-/-</sup> mice) to lupus (B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice), we compared subpopulations of peripheral blood mononuclear cells and spleen cells, also cytokine expression of stimulated spleen cells. <h3>Methods</h3> Peripheral blood mononuclear cells were analyzed by flow cytometry and two distinct subpopulation of Gr-1 positive and negative monocytes were analyzed among B6, B6.<i>Yaa</i>, B6.FcγRIIB<sup>-/-</sup>, and B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice at 2 months of age. Comparisons of cell surface phenotypes of splenic lymphocytes were analyzed using flow cytometry. Spleen cells were triple-stained and the frequency of marginal zone (MZ) B cells, activation/maturation status of B cells, peanut agglutinin (PNA)<sup>+</sup> germinal center (GC) B cells, and CD138<sup>+</sup> plasma cells were analyzed. Also activation/maturation status of T cells, PD1<sup>+</sup>ICOS<sup>+</sup>CD4<sup>+</sup> and PD1<sup>+</sup>CXCR5<sup>+</sup>CD4<sup>+</sup> follicular helper T cells were analyzed. Quantitative real-time PCR analysis was performed to compare mRNA expression levels of notable cytokines in spleen between B6.FcγRIIB<sup>-/-</sup> and B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice at 4 months of age. PMA/ionomycin-stimulated spleen cells from these mice were also analyzed by flow cytometry. <h3>Results</h3> Flow cytometric analysis of peripheral blood monocytes from 2-month-old mice revealed monocytosis in B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice but not in B6.FcγRIIB<sup>-/-</sup> mice. The frequency of Gr-1<sup>-</sup> "resident" monocytes was increased in B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice. Flow cytometric analysis of spleen cells from 4-month-old mice revealed that, while there were no differences in frequencies of B220<sup>+</sup> B cells per total spleen cells among four strains, there was a significant decrease in frequencies of CD21<sup>+</sup>CD23<sup>-</sup> marginal zone B cells in B6.<i>Yaa</i> and B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice. As for the activation/maturation status of B cells, frequencies of CD69<sup>+</sup> activated B cells, PNA<sup>+</sup> GC B cells, and CD138<sup>+</sup> plasma cells were significantly higher in B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice than those found in other strains of mice. As for T cells, the frequency of CD69<sup>+</sup> activated T cells was markedly increased in B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice. As for about comparisons of cytokine synthesis, the expression of IL-6, IL-10 and IL-21 were up regulated in B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice. Both IL-10 and IL-21 were secreted from CD4<sup>+</sup> T cells and the frequencies of IL-10 and IL-21-secreting cells per total CD4<sup>+</sup> T cells were significantly higher in B6.FcγRIIB<sup>-/-</sup>.<i>Yaa</i> mice than those in B6.FcγRIIB<sup>-/-</sup> mice. <h3>Conclusions</h3> The present studies suggest that the mechanism of the disease phenotype conversion from RA to lupus was likely to be due to the activation of monocytes, B cells and T cells leading to the change in cytokine milieus from the activated follicular helper T cells. <h3>Disclosure of Interest</h3> None declared