Attenuation of chronic antiviral T-cell responses through constitutive COX2-dependent prostanoid synthesis by lymph node fibroblasts

Lymphoid T-zone fibroblastic reticular cells (FRCs) actively promote T-cell trafficking, homeostasis, and expansion but can also attenuate excessive T-cell responses via inducible nitric oxide (NO) and constitutive prostanoid release. It remains unclear how these FRC-derived mediators dampen T-cell responses and whether this occurs in vivo. Here, we confirm that murine lymph node (LN) FRCs produce prostaglandin E₂ (PGE₂) in a cyclooxygenase-2 (COX2)-dependent and inflammation-independent fashion. We show that this COX2/PGE₂ pathway is active during both strong and weak T-cell responses, in contrast to NO, which only comes into play during strong T-cell responses. During chronic infections in vivo, PGE₂-receptor signaling in virus-specific cluster of differentiation (CD)8 cytotoxic T cells was shown by others to suppress T-cell survival and function. Using COX2^flox/flox mice crossed to mice expressing Cre recombinase expression under control of the CC chemokine ligand (CCL19) promoter (CCL19cre), we now identify CCL19⁺ FRC as the critical source of this COX2-dependent suppressive factor, suggesting PGE₂-expressing FRCs within lymphoid tissues are an interesting therapeutic target to improve T-cell–mediated pathogen control during chronic infection.