Leukocyte Recruitment to the Inflamed Glomerulus: A Critical Role for Platelet-Derived P-Selectin in the Absence of Rolling

Abstract

The renal glomerulus is one of the few sites within the microvasculature in which leukocyte recruitment occurs in capillaries. However, due to the difficulty of directly visualizing the glomerulus, the mechanisms of leukocyte recruitment to glomerular capillaries are poorly understood. To overcome this, we rendered murine kidneys hydronephrotic to allow the visualization of the functional glomerular microvasculature during an inflammatory response. These experiments demonstrated that following infusion of anti-glomerular basement membrane (GBM) Ab, leukocytes became adherent in glomerular capillaries via a process of immediate arrest, without undergoing prior detectable rolling. However, despite the absence of rolling, this recruitment involved nonredundant roles for the P-selectin/P-selectin glycoprotein ligand-1 and β2 integrin/ICAM-1 pathways, suggesting that a novel form of the multistep leukocyte adhesion cascade occurs in these vessels. Anti-GBM Ab also increased glomerular P-selectin expression and induced a P-selectin-independent increase in platelet accumulation. Moreover, platelet depletion prevented both the increase in glomerular P-selectin, and the leukocyte recruitment induced by anti-GBM Ab. Furthermore, depletion of neutrophils and platelets also prevented the increase in urinary protein excretion induced by anti-GBM Ab, indicating that their accumulation in glomeruli contributed to the development of renal injury. Finally, infusion of wild-type platelets into P-selectin-deficient mice restored the ability of glomeruli in these mice to support leukocyte adhesion. Together, these data indicate that anti-GBM Ab-induced leukocyte adhesion in glomeruli occurs via a novel pathway involving a nonrolling interaction mediated by platelet-derived P-selectin.

Measuring and interpreting platelet-leukocyte aggregates

“…Histochemical and immunofluorescent imaging of frozen or paraffin-embedded tissue sections have provided valuable information about the location of platelet recruitment and PLAs within tissue microenvironments of numerous organs (22,52–55). These techniques, in particular when coupled with advanced confocal or electron microscopy, provide high resolving images to visualise platelet-leukocyte interactions at locations even within opaque tissues of both human and animal origin (Figure 1B).…”

“…Accordingly, some clinical studies (using only a small patient cohort, however) show beneficial effects of anti-platelet therapy in glomerulonephritis patients by reducing circulating platelet aggregates, albuminuria and/or glomerular filtration rate (109–113) and anti-platelet drugs are indeed commonly prescribed in Japanese hospitals to patients with IgA nephropathy (114). The contribution of platelets in the induction of renal inflammation via direct interactions with leukocytes is further supported by the requirement of platelet P-selectin for neutrophil recruitment and/or neutrophil-mediated injury in experimental acute postischemic renal failure (115) and glomerulonephritis (21,22). Neutrophil-depletion on the other hand prevented platelet accumulation within glomerular capillaries in a model of immune-complex-induced glomerulonephritis (22), emphasising the importance of the interplay between platelets and neutrophils during this disease.…”

“…The contribution of platelets in the induction of renal inflammation via direct interactions with leukocytes is further supported by the requirement of platelet P-selectin for neutrophil recruitment and/or neutrophil-mediated injury in experimental acute postischemic renal failure (115) and glomerulonephritis (21,22). Neutrophil-depletion on the other hand prevented platelet accumulation within glomerular capillaries in a model of immune-complex-induced glomerulonephritis (22), emphasising the importance of the interplay between platelets and neutrophils during this disease. Indeed, our unpublished data suggest constitutive on/off interactions between platelets and neutrophils or monocytes in glomerular capillaries (Finsterbusch et al unpublished), leukocyte subsets that both were reported to contribute to renal injury in acute glomerular inflammation (116,117).…”

“…In experimental mouse models and patients with different types of glomerulonephritis platelets accumulate in the kidneys and/or platelet-derived factors are systemically elevated (21,22,105–108). Accordingly, some clinical studies (using only a small patient cohort, however) show beneficial effects of anti-platelet therapy in glomerulonephritis patients by reducing circulating platelet aggregates, albuminuria and/or glomerular filtration rate (109–113) and anti-platelet drugs are indeed commonly prescribed in Japanese hospitals to patients with IgA nephropathy (114).…”

“…Elevated PLA levels are associated with a range of acute and chronic thrombo-inflammatory conditions such as cardiovascular diseases (CVD), acute lung injury (ALI), rheumatoid arthritis, inflammatory bowel disease, stroke, and glomerulonephritis (15–22). Hence, PLAs could become an attractive parameter for diagnostic and/or prognostic analysis.…”