Background: A subset of COPD patients (-pts) has eosinophilia, a trait targeted in clinical drug programs. Yet, little is known about the immunological millieu associated with infiltration of eosinophils (EOS) into COPD lungs.

Aim: To compare the T cell profile between COPD-pts with high (EOS^hi) and low (EOS^low) tissue eosinophilia. 

Methods: EOS were detected in tissue sections from surgically removed lungs from 39 COPD-pts (GOLD I-IV) and 15 non-COPD controls using immunohistochemistry. A subset of the samples underwent single cell transcription factor-based CD4 and CD8 T cell profiling using multiplex immunofluorescence and computerized image analysis. We compared different anatomic lung regions: alveolar tissue (ALV), small airways (SAW) and pulmonary blood vessels (BV).

Results: Median total tissue EOS (%) was significantly increased in COPD-pts (0.41 vs. 0.07, p<0.0001), and the EOS infiltration pattern was generally patchy. Both CD4 and CD8 T cells had complex, partly overlapping and microenvironmentally dictated transcription factor profiles. The EOS^hi group tended to have the highest CD4/CD8 ratio in the whole tissue section and BV regions, while the EOS^low group tended to have the highest ratio in the ALV and SAW regions. Both CD4 and CD8 cells commonly expressed the type-2 promoting transcription factor GATA-3. CD4+/GATA-3+ and CD8+/GATA-3+ cells tended to be increased in the EOS^hi when compared to the EOS^low group in the whole tissue and in all regions except for ALV.

Conclusion: EOS infiltration is common in COPD lungs and seemingly linked to complex T cell transcription factor profiles, where variants of GATA-3+ CD4 and CD8 populations may have important regulatory roles.