Figure 4.

Fnn inhibits CD4⁺ T cell IFN-γ secretion by activating CEACAM1. (A) Schematic representation of the redirected cytokine assay. Mouse mastocytoma P815 cells expressing FcγR were coated with anti-CD3 to enable activation of T cells and subsequent IFN-γ secretion. Cells were incubated with Fnn or the Fnn ∆CbpF mutant at a E:T ratio of 1:600 and IFN-γ secretion was quantified by ELISA after 48 hours of incubation. (B) Flow cytometry staining of primary IL-2 activated human CD4⁺ T cells with anti-CEACAM1 and anti-CD4. Filled grey histograms represent staining with secondary antibody only. (C) Quantification of IFN-γ secretion determined by ELISA. Bars represent means of triplicates ± SD. The graphs represent data collected from two independent experiments. Statistical significance was assessed using a two-tailed unpaired t test. ***p ≤ 0.001. NS, not significant.