Runx3 Regulates CD8⁺ T Cell Local Expansion and CD43 Glycosylation in Mice by H1N1 Influenza A Virus Infection

We have recently reported that transcription factor Runx3 is required for pulmonary generation of CD8⁺ cytotoxic T lymphocytes (CTLs) that play a crucial role in the clearance of influenza A virus (IAV). To understand the underlying mechanisms, we determined the effects of Runx3 knockout (KO) on CD8⁺ T cell local expansion and phenotypes using an inducible general Runx3 KO mouse model. We found that in contrast to the lungs, Runx3 general KO promoted enlargement of lung-draining mediastinal lymph node (mLN) and enhanced CD8⁺ and CD4⁺ T cell expansion during H1N1 IAV infection. We further found that Runx3 deficiency greatly inhibited core 2 O-glycosylation of selectin ligand CD43 on activated CD8⁺ T cells but minimally affected the cell surface expression of CD43, activation markers (CD44 and CD69) and cell adhesion molecules (CD11a and CD54). Runx3 KO had a minor effect on lung effector CD8⁺ T cell death by IAV infection. Our findings indicate that Runx3 differently regulates CD8⁺ T cell expansion in mLNs and lungs by H1N1 IAV infection. Runx3 is required for CD43 core 2 O-glycosylation on activated CD8⁺ T cells, and the involved Runx3 signal pathway may mediate CD8⁺ T cell phenotype for pulmonary generation of CTLs.