LPS-pretreated BMDCs were cocultured 7 days with anti-CD3/CD28–stimulated WT (A–F) or Lfa1-KO (C and D) CD4⁺ T cells, with or without DEL-1–Fc, DEL-1[RGE]-Fc, or Fc control (see Methods). Cells were analyzed by FACS: Representative plots (A and C) and frequencies of Tfh cells, defined as CD4⁺CXCR5⁺PD-1^hiBCL6^hi (B) or as CD4⁺CXCR5⁺PD-1^hi (D, left) or CD4⁺CXCR5⁺ICOS⁺ (D, right). (E) FACS histograms and BCL6 MFI in CD4⁺CXCR5⁺PD-1^hi T cells. (F) FACS plots (left) and frequencies of pSTAT3⁺ cells in CD4⁺CXCR5⁺PD-1^hi T cells (middle) and pSTAT3 MFI (right). (G) CIA was induced in ColVI-Del1 mice and WT littermates and after 10 days inguinal LN mononuclear cells were analyzed: Representative plots (left) and frequencies of pSTAT3⁺ cells in Tfh cells (middle) and pSTAT3 MFI (right). (H) Binding of ICAM-1-Fc to Tfh cells (from LNs of mice subjected to CIA) in the presence of DEL-1 or BSA control (see Methods). (I and J) Using the coculture system described above (A–F) with WT CD4⁺ T cells, the cells were analyzed after 3-day incubation: (I) FACS plots (left), frequencies of pZAP70⁺ cells (middle), and pZAP70 MFI (right) in CD4⁺CXCR5⁺PD-1^hi T cells. (J) FACS plots (left) and frequencies of Ki67⁺ cells in CD4⁺CXCR5⁺PD-1^hi T cells (right). (K and L) CIA was induced in ColVI-Del1 mice and WT littermates and after 10 days, inguinal LN mononuclear cells were analyzed: FACS plots (K and L, left), frequencies of pZAP70⁺ (K, middle), or Ki67⁺ (L, right) cells and pZAP70 MFI (K, right) in Tfh (CD4⁺CXCR5⁺PD-1^hi) cells. Data are the mean ± SD (B, E, F, I, and J n = 6 cocultures/group; D, n = 8 cocultures; G, K, and L n = 6 mice/group, all from 2 independent experiments; H, n = 6 cultures/group. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. One-way ANOVA with Tukey’s (B and D) or Dunnett’s post test (H); Student’s unpaired t test (E, F left, G, I left, J, K, and L); and Mann-Whitney U test (F and I right).