Fig 2.

ICOS⁺ CXCR5⁺ T_FH coexpressing CXCR4 are induced in response to infection. MedLN isolated from BALB/c mice (n = 4) at 10 days postinfection with influenza virus A/Mem71 were analyzed by 8- to 10-color flow cytometry. Shown are 5% contour plots with outliers of a representative sample from one of at least two repeat experiments (n = 4 each). (A) Gates used to identify CD4⁺ ICOS⁺ T cells expressing CXCR5 and/or CXCR4. SSC, side scatter; FSC, forward scatter. (B) CD4⁺ T cells were further analyzed to display the frequency of ICOS⁺ CXCR5⁺ cells coexpressing CXCR4 (left) and ICOS⁺ CXCR4⁺ cells coexpressing CXCR5 (right). (C) Expression levels of ICOS and CCR7 were examined on CD4⁺ T cells (left). The bar chart indicates mean fluorescent intensities (MFI) ± SD for CCR7 on the indicated CD4⁺ T cell populations. (D) ICOS, CXCR5, and CXCR4 expression levels in CD4⁺ CD62L⁻ PSGL-1^low cells were analyzed. The bar chart represents the mean frequencies ± SD for the four ICOS⁺ populations identified by CXCR5 and CXCR4 expression among cells indicated on the x axis.