AbstractBackgroundMucosal-associated invariant T (MAIT) cells and Vδ2+γδ T cells are anti-bacterial innate-like lymphocytes (ILLs) that are enriched in blood and mucosa. ILLs have been implicated in control of bacterial infection. However, the role of ILLs in community-acquired pneumonia (CAP) is unknown.MethodsUsing sputum samples from a well-characterised CAP cohort, MAIT cell (Vα7.2-Jα12/20/33) and Vδ2+T cell (Vδ2-Jδ1/2/3/4) abundance was determined by quantitative PCR. Cytokine and chemokine concentrations in sputum were measured. The capacity of bacteria in sputum to produce activating ligands for MAIT cells and Vδ2+T cells was inferred by 16S rRNA sequencing.ResultsMAIT cell abundance in sputum was higher in patients with less severe pneumonia; duration of hospital admission was inversely correlated with both MAIT and Vδ2+T cell abundance. The abundance of both ILLs was higher in patients with a confirmed bacterial aetiology, however there was no correlation with total bacterial load or the predicted capacity of bacteria to produce activating ligands. Sputum MAIT cell abundance was associated with interferon- α, and interferon-γ, and sputum neutrophil abundance, while Vδ2+T cell abundance was associated with CXCL11 and interferon-γ.ConclusionsPulmonary MAIT and Vδ2+T cells can be detected in sputum in CAP, where they may contribute to improved clinical outcome.