3.6 Neutralizing IL-7 in lung retarded silicosis progression
through disrupting the pathogenic TRM-Teff cell
maintenance.
Now that the CS-induced pathogenic
CD4+TRM cells expandedin situ , we next explored interventions targeting their
maintenance in the lung, in which IL-7 was reported to be essential[34]. Hence, we first examined the IL-7R (CD127)
levels on the CD4+ TRM cells in
silicotic lung. Expectedly, CD4+ TRMcells expressed higher levels of IL-7R compared to those of the naïve T
cells (CD44–). Strikingly, within
CD4+ TRM cells, TRM-
Teff cells but not Tregs expressed a higher level of IL-7R indicating a
high demand for IL-7 of those Teff cells (Fig 6A). We then treated the
silicotic mice with IL-7-neutralizing antibody through intratracheal
(i.t. ) instillation (Fig 6B). To gain insights, we sorted
CD4+ T cells from the lungs and spleens and did qPCR
analysis. Significantly, in the treated pulmonary
CD4+T cells, we observed alleviated Th1 and
Th17-related transcripts (Tbx21 , Ifng , Il2 ,Rorc and Il17a ), as well as decreased mRNA levels
associated with cell activation (Icos , Ctla4 ,Klrg1 , and Pdcd1 ). Additionally, the cell retention
markers (Cxcr6 and Itgae ) were decreased, implying a
reduction of TRM cells (Fig 6C). Strikingly, the
anti-IL-7 treatment augmented Il10 transcripts, suggesting
suppressive inflammatory responses, while markers related to Treg cells,Foxp3, and Areg were unaltered (Fig 6C). However, these
effects were diminished in the splenic CD4+ T cells (Fig 6D), suggesting
that pulmonary local IL-7 neutralization did not affect immune response
in other organs.
To confirm the transcriptional changes, we further did flow cytometric
analysis to the pulmonary CD4+ TRMcells but did not observe reduced TRM cells in the lung
(Fig 6E), while the ratio of CD103– to
CD103+ in
CD69+CD4+ TRM cells
was decreased (Fig 6F), suggesting TRM-Teff cells were
restrained. However, we did not observe a significantly altered ratio of
TRM-Tregs within CD4+TRM (Fig 6G). To ascertain the effects on
TRM-Teff cells, we scrutinized the composition of T cell
subsets. Consistent with the transcript data, pulmonary IL-7
neutralization blunted T-bet+ Th1-type
TRM, but not the ROR-γt+ Th17-type
TRM cells albeit with an increasing trend (Fig 6H).
Additionally, pulmonary IL-7 neutralization decreased Ki67 levels of
TRM-Teff cells (Fig 6I), confirming that IL-7 plays a
positive role in TRM cell proliferation[35].
Last, to gain insight into the profound effect of IL-7 neutralization on
silicosis, lung histological analysis was performed. Expectedly, local
anti-IL-7 treatment in the lung mitigated disease phenotype with reduced
cell accumulation and cellular nodule formation (Fig 6J), as well as
attenuated collagen deposition revealed by Masson’s trichrome staining
(Fig 6K). Consistent with previous sorted cells transcript results, in
the lung tissue, the Th1-related cytokine (Ifng ) and
transcriptional factors (Tbx21 ) transcripts were blunted (Fig
6L). The neutralization decreased the transcripts of Il17adespite exerting no effects on those of Rorc in the lung (Fig
6L), implying that pulmonary IL-7 neutralization alleviated CS
particles-induced inflammatory response. In accordance with alleviated
fibrosis, the declined Col1a1 and Fibronectin transcripts
in the lung further validated the conclusion (Fig 6M). Collectively,
these data demonstrated that the maintenance of TRM-Teff
cells depended on IL-7 in the lung. Targeting IL-7 would be a potential
intervention against CS-induced pulmonary fibrosis.