The present study analyzed the effect of CD4⁺ Forkhead box protein 3 negative (Foxp3⁻) T-cells and Foxp3⁺ CD4⁺ T-cells on infarct size in a mouse myocardial ischemia-reperfusion model.

We examined the infarct size as a fraction of the area-at-risk as primary study endpoint in mice after 30 minutes of coronary ligation followed by 24 hours of reperfusion. CD4⁺ T-cell deficient MHC-II KO mice showed smaller histologically determined infarct size (34.5 ± 4.7% in MHCII KO versus 59.4 ± 4.9% in wildtype (WT)) and better preserved ejection fraction determined by magnetic resonance tomography (56.9 ± 2.8% in MHC II KO versus 39.0 ± 4.2% in WT). MHC-II KO mice also displayed better microvascular perfusion than WT mice after 24 hours of reperfusion. Also CD4⁺ T-cell sufficient OT-II mice, which express an in this context irrelevant T-cell receptor, revealed smaller infarct sizes compared to WT mice. However, MHC-II blocking anti-I-A/I-E antibody treatment was not able to reduce infarct size indicating that autoantigen recognition is not required for the activation of CD4⁺ T-cells during reperfusion. Flow-cytometric analysis also did not detect CD4⁺ T-cell activation in heart draining lymph nodes in response to 24 hours of ischemia-reperfusion. Adoptive transfer of CD4⁺ T-cells in CD4 KO mice increased the infarct size only when including the Foxp3⁺ CD25⁺ subset. Depletion of CD4⁺ Foxp3⁺ T-cells in DEREG mice enabling specific conditional ablation of this subset by treatment with diphtheria toxin attenuated infarct size as compared to diphtheria toxin treated WT mice.

CD4⁺ Foxp3⁺ T-cells enhance myocardial ischemia-reperfusion injury. CD4⁺ T-cells exert injurious effects without the need for prior activation by MHC-II restricted autoantigen recognition.