FIGURE 4.

Lin⁻c-Kit⁺_pure cells increase production of IgG autoantibodies, expand Tfh cells and play pathogenic role in lupus disease. In vitro helper assay: (A) Lin⁻c-Kit⁺ cells (APC) increased production of IgG autoantibodies by lupus T and B cells upon nucleosome stimulation in 7-day helper assay (Methods), and (B) Lin⁻c-Kit⁺ cells also activated T cells and B cells to produce IgG autoantibodies in cocultures as shown after processing/presenting apoptotic thymocytes at different ratios. (C) % of Tfh cell expansion by Lin⁻c-Kit⁺cells. Three days after co-culturing Lin⁻c-Kit⁺cells and T cells with nucleosomes or PBS, cells were stained for ICOS, CXCR5 and PD-1 to identify Tfh cells. Lin⁻c-Kit⁺cells expanded Tfh cells in both CD4⁺ and γδT cell populations upon stimulation with nucleosomes, but Tfh cells were not expanded without APCs (T only). Mean ± s.e.m of 3 experiments, n= 15 mice. (D–F) Lin⁻c-Kit⁺_pure cells accelerate severe lupus nephritis on adoptive transfer; and markedly increased pathogenic IgG autoantibody levels in sera of recipients (E, F). Arrows indicate the time of adoptive cell transfer. Number of mice/group = 6; except Saline control group = 15. CD11b = CD11b⁺ CD11c ^{low or −} CD117 ^{low or −} cells; L⁻K+cells = Lin⁻c-Kit⁺_pure cells; Nuc: nucleosomes.