Hepatocyte Growth Factor Receptor c-Met Instructs T Cell Cardiotropism and Promotes T Cell Migration to the Heart via Autocrine Chemokine Release.

Effector-T-cell-mediated immunity depends on the efficient localization of antigen-primed lymphocytes to antigen-rich non-lymphoid tissue, which is facilitated by the expression of a unique set of "homing" receptors acquired by memory T cells. We report that engagement of the hepatocyte growth factor (HGF) receptor c-Met by heart-produced HGF during priming in the lymph nodes instructs T cell cardiotropism, which was associated with a specialized homing "signature" (c-Met(+)CCR4(+)CXCR3(+)). c-Met signals facilitated T cell recruitment to the heart via the chemokine receptor CCR5 by inducing autocrine CCR5 ligand release. c-Met triggering was sufficient to support cardiotropic T cell recirculation, while CCR4 and CXCR3 sustained recruitment during heart inflammation. Transient pharmacological blockade of c-Met during T cell priming led to enhanced survival of heart, but not skin, allografts associated with impaired localization of alloreactive T cells to heart grafts. These findings suggest c-Met as a target for development of organ-selective immunosuppressive therapies.

Self-recognition of the endothelium enables regulatory T-cell trafficking and defines the kinetics of immune regulation.

Localization of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells to lymphoid and non-lymphoid tissue is instrumental for the effective control of immune responses. Compared with conventional T cells, Treg cells constitute a minute fraction of the T-cell repertoire. Despite this numeric disadvantage, Tregs efficiently migrate to sites of immune responses reaching an optimal number for the regulation of T effector (Teff) cells. The array and levels of adhesion and chemokine receptor expression by Tregs do not explain their powerful migratory capacity. Here we show that recognition of self-antigens expressed by endothelial cells in target tissue is instrumental for efficient Treg recruitment in vivo. This event relies upon IFN-γ-mediated induction of MHC-class-II molecule expression by the endothelium and requires optimal PI3K p110δ activation by the T-cell receptor. We also show that, once in the tissue, Tregs inhibit Teff recruitment, further enabling a Teff:Treg ratio optimal for regulation.

Normal physiological and pathophysiological effects of trypan blue on the retinas of albino rabbits.

PURPOSE: To determine whether intravitreal injection of trypan blue is toxic to the retina of the albino rabbit. METHODS: Sixteen albino rabbits were studied for the effects of intravitreal trypan blue (eight with 0.06% solution and eight with 0.15% solution). Saline was injected into the fellow control eye of all rabbits. The electroretinogram and visual evoked potentials were recorded from each rabbit at different time intervals after injection. The rabbits were killed at the termination of the follow-up period, and their retinas were prepared for histologic examination under light microscopy. RESULTS: In all rabbits, short-term follow-up showed significant reduction of ERG responses in the experimental eye, with the b-wave more affected than the a-wave. Partial to complete recovery was observed during follow-up. After 4 weeks, negligible ERG deficit was observed in the rabbits treated with 0.06% trypan blue, whereas significant ERG deficit was measured in rabbits tested by the 0.15% trypan blue. No differences in flash VEP responses between experimental and control rabbit eyes were found. Light microscopy showed no significant histologic effects in the retinas exposed to the 0.06% solution. Marked disorganization of all retinal layers was observed in areas close to the site of injection in the rabbits injected with the 0.15% solution. CONCLUSIONS: Trypan blue exerts transient physiological effects on the distal retina of the rabbit, but in concentrations of 0.15% it can induce permanent toxic effects. Therefore, caution should be used when using this dye in vitreoretinal surgery.

Retinal toxicity of commercially available intravitreal ketorolac in albino rabbits.

PURPOSE: To determine whether intravitreal injection of a commercially available ketorolac tromethamine preparation causes retinal toxicity in albino rabbits. METHODS: Nine albino rabbits were injected intravitreally with ketorolac tromethamine (3 mg; 0.1 mL) in one eye and saline (0.1 mL) in the fellow eye. Six of the rabbits received a single injection of ketorolac, and the other three rabbits underwent biweekly injection for a total of four injections. Electroretinography testing was performed on both eyes at different time intervals during 4 weeks of follow-up in the single injection group, and during 12 weeks of follow-up in the multiple injection group. Visual evoked potentials were recorded from each rabbit using monocular and binocular stimulation at the end of the follow-up period. Animals were then killed, and the retinas were prepared for morphologic examination at the light microscope level and for immunostaining for glial fibrillary acidic protein, as a marker of retinal damage. RESULTS: The electroretinography responses from the control and experimental eyes were similar throughout the follow-up period in all rabbits of both experimental groups. There were no differences in the flash visual evoked potential responses between experimental and control eyes in the single injection group, while in the repeated injection group, statistically significant differences were found. Light microscopy did not identify significant histologic differences between the retinas from control and experimental eyes after a single dose. However, after repeated dosing, two of three eyes showed histologic evidence of local toxicity. Immunocytochemical analysis showed no glial fibrillary acidic protein staining in Muller (glial) cells throughout the retina in the single injection group. Slight glial fibrillary acidic protein staining was detected in only one of the three retinas from rabbits in the repeated injection group. CONCLUSIONS: Commercially available ketorolac tromethamine was found to be toxic to the retinas of albino rabbits following multiple intravitreal injections at a dose of 3 mg while no electrophysiologic toxicity was found. Therefore, the use of commercially available ketorolac containing alcohol, for intravitreal injection is not recommended.