Spatial and temporal variation in macroparasite communities of three-spined stickleback.

Patterns in parasite community structure are often observed in natural systems and an important question in parasite ecology is whether such patterns are repeatable across time and space. Field studies commonly look at spatial or temporal repeatability of patterns, but they are rarely investigated in conjunction. We use a large dataset on the macroparasites of the three-spined stickleback, Gasterosteus aculeatus L., collected from 14 locations on North Uist, Scotland over an 8-year period to investigate: (1) repeatability of patterns in parasite communities among populations and whether variation is consistent across years, (2) whether variation between years can be explained by climatic variation and progression of the season and (3) whether variation in habitat characteristics explain population differences. Differences in relative abundance and prevalence across populations were observed in a number of parasites investigated indicating a lack of consistency across years in numerous parasite community measures; however, differences between populations in the prevalence and abundance of some parasites were consistent throughout the study. Average temperature did not affect parasite community, and progression of the season was only significant for two of 13 community measures. Two of the six habitat characteristics investigated (pH and calcium concentration) significantly affected parasite presence.

Annexin 1-deficient neutrophils exhibit enhanced transmigration in vivo and increased responsiveness in vitro.

The role of the endogenous anti-inflammatory mediator annexin 1 (AnxA1) in controlling polymorphonuclear leukocyte (PMN) trafficking and activation was addressed using the recently generated AnxA1 null mouse. In the zymosan peritonitis model, AnxA1 null mice displayed a higher degree (50-70%) of PMN recruitment compared with wild-type littermate mice, and this was associated with reduced numbers of F4/80+ cells. Intravital microscopy analysis of the cremaster microcirculation inflamed by zymosan (6 h time-point) indicated a greater extent of leukocyte emigration, but not rolling or adhesion, in AnxA1 null mice. Real-time analysis of the cremaster microcirculation did not show spontaneous activation in the absence of AnxA1; however, superfusion with a direct-acting PMN activator (1 nM platelet-activating factor) revealed a subtle yet significant increase in leukocyte emigration, but not rolling or adhesion, in this genotype. Changes in the microcirculation were not secondary to alterations in hemodynamic parameters. The phenotype of the AnxA1 null PMN was investigated in two in vitro assays of cell activation (CD11b membrane expression and chemotaxis): the data obtained indicated a higher degree of cellular responses irrespective of the stimulus used. In conclusion, we have used a combination of inflammatory protocols and in vitro assays to address the specific counter-regulatory role of endogenous AnxA1, demonstrating its inhibitory control on PMN activation and the consequent impact on the inflamed microcirculation.

PECAM-1, alpha6 integrins and neutrophil elastase cooperate in mediating neutrophil transmigration.

The heterogeneous nature of the perivascular basement membrane (composed primarily of laminin and collagen type IV) suggests the existence of an elaborate array of adhesive interactions and possibly proteolytic events in leukocyte migration through this barrier. In this context, blockade of alpha6 integrins (laminin receptors), neutrophil elastase (NE) or both inhibited neutrophil migration through interleukin-1beta (IL-1beta)-stimulated mouse cremasteric venules, as observed by intravital microscopy. Furthermore, analysis of tissues by confocal microscopy indicated a synergistic role for alpha6 integrins and NE in mediating neutrophil migration through the perivascular basement membrane. Using a combined in vitro and in vivo experimental approach, the findings of this study also suggest that alpha6 integrins and NE are mobilized from intracellular stores to the cell surface of transmigrating mouse neutrophils, although these events occur via mechanisms dependent on and independent of platelet/endothelial-cell adhesion molecule 1 (PECAM-1, CD31), respectively. Despite different regulatory mechanisms, blockade of alpha6 integrins or NE inhibited migration of murine neutrophils through laminin-coated filters in vitro. Collectively, the findings suggest that, whereas regulation of the expression of alpha6 integrins and NE occur via different adhesive mechanisms, these molecules might act in a cooperative manner in mediating neutrophil migration through venular walls, in particular the perivascular basement membrane.

Neutrophil elastase (NE)-deficient mice demonstrate a nonredundant role for NE in neutrophil migration, generation of proinflammatory mediators, and phagocytosis in response to zymosan particles in vivo.

Neutrophil elastase (NE) remains a controversial player in the process of leukocyte transmigration and much of this controversy stems from conflicting reports on the effects of NE inhibitors. The availability of NE-deficient mice (NE(-/-)) provides a clean and elegant tool for the study of leukocyte migration in vivo. In this study, NE(-/-) mice were used to investigate the role of NE in leukocyte migration through cremasteric venules, as observed by intravital microscopy, induced by locally administered cytokines IL-1beta and TNF-alpha and the particulate stimulus, zymosan. Although no defects in leukocyte responses induced by the cytokines were observed, zymosan-induced leukocyte firm adhesion and transmigration was suppressed in NE(-/-) mice. These responses were also inhibited in wild-type mice when zymosan was coinjected with a specific NE inhibitor. Quantification of inflammatory mediator levels in homogenates of zymosan-stimulated tissues indicated reductions in levels of IL-1beta, KC, and macrophage inflammatory protein-1alpha in NE(-/-) mice. Furthermore, phagocytosis of fluorescent zymosan particles, as observed by intravital microscopy, was diminished in NE-deficient animals. Collectively, the findings of this study indicate a nonredundant role for NE in zymosan-induced leukocyte firm adhesion and transmigration, and that this defect is associated with impaired generation of proinflammatory mediators as well as phagocytosis of zymosan particles in vivo.

Migration of leukocytes through the vessel wall and beyond.

The migration of leukocytes from the vascular lumen to sites of infection and/or injury in the extravascular tissue involves a series of sequential and coordinated molecular and cellular events with the resultant primary response being that of reduced leukocyte velocity within the blood stream, followed by leukocyte firm adhesion to endothelial cells lining the vessel wall and eventually migration through the vessel wall. Despite the growing knowledge of the mechanisms that mediate initial interaction of leukocytes with the endothelium, very little is known about the mechanisms that mediate and regulate leukocyte migration through the venular wall, the endothelium and its associated perivascular basement membrane. This review, whilst giving a brief outline of the stepwise cascade of molecular interactions involved in this process and the methods employed to investigate leukocyte migration in vivo, focuses primarily on mechanisms of leukocyte transmigration, the final step in the process of leukocyte emigration. Furthermore, special emphasis is placed on discussing the process and the mechanisms involved in leukocyte migration through the basement membrane, a structure that presents significant impedance to transmigrating leukocytes but is seldom investigated in the context of leukocyte transmigration in vivo. The review also discusses the growing evidence supporting the concept that leukocyte transmigration is not only a response that describes the passage of leukocytes through the venular wall, but also acts as a means of regulating leukocyte responsiveness beyond the vessel wall, i.e. within the extravascular tissue.