Lymphocyte migration into cell-mediated immune lesions is inhibited by trypsin

A liver perfusion model for studies of selective adherence and transient halting of portal blood leukocytes in sinusoids

Portal blood leukocytes play an important, but still poorly defined, role in the immune processes of the liver. In our previous studies, we showed that certain leukocyte subsets are selectively halted in the liver. These cells marginate in sinusoids and, together with resident Kupffer and endothelial sinusoidal cells, participate in antiviral and antitumor processes. The molecular mechanisms of margination and cooperation with resident sinusoidal cells require clarification. However, in vivo harvesting of portal blood leukocytes is associated with cumbersome cannulation of portal and hepatic veins and manipulation of the liver, causing major disturbances in splanchnic blood flow and liver blood supply, totally distorting sinusoidal blood perfusion and leukocyte margination. To overcome these difficulties, we have developed an in situ normothermic rat liver perfusion model permitting quantitative observations of blood leukocyte extraction in sinusoids. First, liver was flushed through the portal vein and the effluent leukocytes, named liver-associated leukocytes (LAL1), were collected from hepatic veins. Then, the liver was perfused for 60 min with 50 ml of blood using a semiclosed perfusion system. Upon completion of perfusion, the liver portal vasculature was flushed again to retrieve the leukocytes extracted from the perfusing blood (LAL2). These cells were characterized with respect to their phenotype and cytotoxicity. The mean leukocyte count of the washout before perfusion was 1.04+/-0.2x10(6)/g of liver tissue and 0.9+/-0.1x10(6)/g after 60 min of perfusion, indicating retention by the perfused liver, the live leukocyte extracting capacity. To further evaluate the efficiency of perfusion, FITC-labelled leukocytes were added to the perfusing leukocyte-free blood. Around 95% of the postperfusion washout LALs were FITC(+). Heat-killed leukocytes did not marginate in sinusoids. Preincubation of leukocytes with substances able to lower adhesion capacity, such as lidocaine, trypsin and AAGM1, significantly decreased the postperfusion LAL2 washout population. The numbers of extracted postperfusion LAL2 CD5(+), CD4(+), CD8(+), CD56(+) and class II(+) subsets did not differ statistically from those of preperfusion LAL1. Moreover, the cytotoxicity of LAL2 and LAL1 against CC531 and K562 remained at a similar level. Thus, perfused liver also retained its selective leukocyte extraction capacity. This model shows that the process of selective margination of portal blood cell subsets in the liver can be studied in an artificially perfused liver subject to physiological blood flow parameters, temperature, oxygenation and minimal ischemic time before connection to the perfusion device. Furthermore, it is suitable for studies of the selective recruitment of blood cells in sinusoids in a wide large of situations including liver tumors, infections, rejection after transplantation, graft vs. host disease, as well as in the investigation of the effect of drugs on these processes.

Proteinase-activated receptor 2 is an anti-inflammatory signal for colonic lamina propria lymphocytes in a mouse model of colitis

The proteinase-activated receptor 2 (PAR-2) is a member of a family of G protein-coupled receptors for proteases. Proteases cleave PARs within the extracellular N-terminal domains to expose tethered ligands that bind to and activate the cleaved receptors. PAR-2 is highly expressed in colon in epithelial and neuronal elements. In this study we show that PAR-2 activation prevents the development and induces healing of T helper cell type 1-mediated experimental colitis induced by intrarectal administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) in mice. A role for PAR-2 in the protection against colon inflammation was explored by the use of SLIGRL-NH(2), a synthetic peptide that corresponds to the mouse tethered ligand exposed after PAR-2 cleavage. TNBS-induced colitis was dose-dependently reduced by the administration of SLIGRL-NH(2), whereas the scramble control peptide, LSIGRL-NH(2), was uneffective. This beneficial effect was reflected by increased survival rates, improvement of macroscopic and histologic scores, decrease in mucosal content of T helper cell type 1 cytokines, protein, and mRNA, and a diminished myeloperoxidase activity. SLIGRL-NH(2), but not the scramble peptide, directly inhibited IFN-gamma secretion and CD44 expression on lamina propria T lymphocytes. Protection exerted by PAR-2 in TNBS-treated mice was reverted by injecting mice with a truncated form of calcitonin gene-related peptide and by sensory neurons ablation with the neurotoxin capsaicin. Collectively, these studies show that PAR-2 is an anti-inflammatory receptor in the colon and suggest that PAR-2 ligands might be effective in the treatment of inflammatory bowel diseases.

Functional and morphological changes in post-capillary venules in relation to lymphocytic infiltration into BCG-induced granulomata in rat skin

Vessels identical to lymph node high endothelial venules (HEV) have been described in sites of non-lymphoid tissue lymphocyte accumulation. In this study the function of these (HEV-like) vessels has been investigated in BCG-induced skin lesions in the rat. By following the traffic of radiolabelled lymphocytes from the blood into the lesions the HEV-like vessels have been shown to be the preferred site of migration. The complicated development of the vessels has been studied and an hypothesis advanced to explain their inter-relationship with tissue and circulating lymphocytes.

Some mechanisms of disturbances and recovery of T-lymphocyte migratory properties in irradiated mice

Migration of 51Cr-labelled T cells from irradiated mice into lymph nodes of syngeneic unirradiated recipients decreased in a dose-dependent fashion. Influx of labelled T cells between 4 and 24 hr after injection (secondary migration) is more radiosensitive than lymph-node migration of T cells in the first 4 hr (primary migration). Treatment of T cells from irradiated mice in vitro with Con A or with trypsin does not enhance radiation-induced alteration of their migratory properties, but irradiation enhances the effects of Con A and trypsin on T-cell migration. Recovery of primary migration of irradiated T cells is completed 3 months after irradiation; it is probably caused by T-cell renewal. The defect of T-cell secondary migration is more stable: it remains 6 months after irradiation in a dose of 4 Gy. Post-irradiation defects of the T-cell differentiation process as a cause of long-lasting alteration of T-cell secondary migration are discussed.

Changes in vascular endothelium related to lymphocyte collections in diseased synovia

A population of small blood vessels are described in the synovia of patients with a number of different arthropathies. These vessels are identical to the high endothelial venules (HEV) of lymph node paracortex, known to be the site of lymphocyte diapedesis from blood to tissues. The significance of this finding and its possible role in the pathogenesis of inflammatory arthritides are discussed.