During viral infections, chemokines guide activated effector T cells to infection sites. However, the cells responsible for producing these chemokines and how such chemokines recruit T cells is unknown. Here, we show that the early recruitment of neutrophils into influenza-infected trachea is essential for CD8+ T cell-mediated immune protection in mice. We observed that migrating neutrophils leave behind long-lasting trails that are enriched in the chemokine CXCL12. Experiments with granulocyte-specific CXCL12 conditional knock-out mice and a CXCR4 antagonist revealed that CXCL12 derived from neutrophil trails is critical for virus-specific CD8+ T cell recruitment and effector functions. Collectively, these results suggest neutrophils deposit long-lasting, chemokine-containing trails, which may provide both chemotactic and haptotactic cues for efficient CD8+ T cell migration and localization in influenza-infected tissues.

Opening of the mitochondrial permeability transition pore (MPTP) is thought to be a critical event in mediating the damage to hearts that accompanies their reperfusion following prolonged ischaemia. Protection from reperfusion injury occurs if the prolonged ischaemic period is preceded by short ischaemic periods followed by recovery. Here we investigate whether such ischaemic preconditioning (IPC) is accompanied by inhibition of MPTP opening. MPTP opening in Langendorff-perfused rat hearts was determined by perfusion with 2-deoxy[ We demonstrate that IPC inhibits initial MPTP opening in hearts reperfused after 30 min global ischaemia, and subsequently enhances pore closure as hearts recover. However, MPTP opening in mitochondria isolated from IPC hearts occurred more readily than control mitochondria, implying that MPTP inhibition by IPC in situ was secondary to other factors such as decreased calcium overload and oxidative stress. Hearts perfused with cyclosporin A or sanglifehrin A, powerful inhibitors of the MPTP, also recovered better from ischaemia than controls (improved haemodynamic function and less lactate dehydrogenase release). However, the mitochondrial DOG entrapment technique showed these agents to be less effective than IPC at preventing MPTP opening. Our data suggest that protection from reperfusion injury is better achieved by reducing factors that induce MPTP opening than by inhibiting the MPTP directly.

Studies with different ATP-sensitive potassium (K ATP ) channel openers and blockers have implicated opening of mitochondrial K ATP (mitoK ATP ) channels in ischaemic preconditioning (IPC). It would be predicted that this should increase mitochondrial matrix volume and hence respiratory chain activity. Here we confirm this directly using mitochondria rapidly isolated from Langendorffperfused hearts. Pre-ischaemic matrix volumes for control and IPC hearts (expressed in ml per mg protein ± S.E.M., n = 6), determined with 3 H 2 O and [14 C]sucrose, were 0.67 ± 0.02 and 0.83 ± 0.04 (P < 0.01), respectively, increasing to 1.01 ± 0.05 and 1.18 ± 0.02 following 30 min ischaemia (P < 0.01) and to 1.21 ± 0.13 and 1.26 ± 0.25 after 30 min reperfusion. Rates of ADP-stimulated (State 3) and uncoupled 2-oxoglutarate and succinate oxidation increased in parallel with matrix volume until maximum rates were reached at volumes of 1.1 ml ml _1 or greater. The mitoK ATP channel opener, diazoxide (50 mM), caused a similar increase in matrix volume, but with inhibition rather than activation of succinate and 2-oxoglutarate oxidation. Direct addition of diazoxide (50 mM) to isolated mitochondria also inhibited State 3 succinate and 2-oxoglutarate oxidation by 30 %, but not that of palmitoyl carnitine. Unexpectedly, treatment of hearts with the mitoK ATP channel blocker 5-hydroxydecanoate (5HD) at 100 or 300 mM, also increased mitochondrial volume and inhibited respiration. In isolated mitochondria, 5HD was rapidly converted to 5HD-CoA by mitochondrial fatty acyl CoA synthetase and acted as a weak substrate or inhibitor of respiration depending on the conditions employed. These data highlight the dangers of using 5HD and diazoxide as specific modulators of mitoK ATP channels in the heart.

Significance Precise regulation of chemokine signal is critical for directional migration of cells. In the study of complex cell behavior, it remains difficult to manipulate chemokine activity at precise times and places within living animals, and it is not possible to study different chemokine effects on defined cell types over a range of timescales. Furthermore, a given chemokine can activate multiple chemokine receptors and vice versa. Here we developed a photoactivatable chemokine receptor that can induce highly specific chemokine signals and guide cell migration toward the light stimulation. This work will advance our understanding of the cell migration process with a number of previously unidentified findings. Clinically, our photoactivatable chemokine receptor approach may have broad applications for adoptive cell transfer therapy.

No abstract