GL7 ligand expression defines a novel subset of CD4+TRMcells in lungs recovered from pneumococcus

Streptococcus pneumoniaeis the most common etiology of bacterial pneumonia, one of the leading causes of death in children and the elderly worldwide. During non-lethal infections with S. pneumoniae, lymphocytes accumulate in the lungs and protect against reinfection with serotype-mismatched strains. Cluster of differentiation CD4+resident memory T (TRM) cells are known to be crucial for this protection, but the diversity of lung CD4+TRMcells has yet to be fully delineated. We aimed to identify unique subsets and their contributions to lung immunity. After recovery from pneumococcal infections, we identified a distinct subset of CD4+T cells defined by the phenotype CD11ahiCD69+GL7+in mouse lungs. Phenotypic analyses for markers of lymphocyte memory and residence demonstrated that GL7+T cells are a subset of CD4+TRMcells. Functional studies revealed that unlike GL7−TRMsubsets that were mostly (RAR-related Orphan Receptor gamma T) RORγT+, GL7+TRMcells exhibited higher levels of (T-box expressed in T cells) T-bet and Gata-3, corresponding with increased synthesis of interferon-γ, interleukin-13, and interleukin-5, inherent to both T helper 1 (TH1) and TH2 functions. Thus, we propose that these cells provide novel contributions during pneumococcal pneumonia, serving as important determinants of lung immunity.