Human Mϕs induce PC differentiation through IP-10. (A) Sorted naive B cells were co-cultured with fixed Mϕs or medium and/or with supernatants from Mϕ–B cell co-cultures. These were analyzed for PC phenotype and counts. (B) Luminex assay for the cytokines and chemokines in the supernatants from Mϕ–B cell co-cultures. (C) Naive B cells and Mϕs were cultured for 48 h. B cells and Mϕs were sorted for the extraction of total RNA, and qPCR was performed to measure the mRNA of IL-6 and IP-10. Data are relative expression of IL-6 or IP-10 normalized to the housekeeping gene GAPDH. Each dot represents data generated from a different donor. (D) Sorted naive B cells were co-cultured with autologous Mϕs in the presence of neutralizing Abs against IP-10, IL-6/IL-6R, or control mouse IgG1. The PC phenotype and absolute cell numbers for PCs are shown. (E) Summary of independent experiments using cells from different donors. Error bars indicate SEM of six different experiments. **, P = 0.001 (anti–IP-10) and P = 0.0002 (anti–IL-6), one-sample Student’s t test. (F) Sorted naive B cells were co-cultured with fixed Mϕs in the presence of recombinant human IP-10 or IL-10 and analyzed for PC counts. Data represent similar results from at least three independent experiments using different donors. (A, B, and D–F) Mean ± SD of duplicate (A, D, and F) or triplicate (B) cultures is shown.