Detection and chromatographic removal of lipopolysaccharide in preparations of multifunctional galectins.

The functional spectrum of human galectins is currently explored, with a wide range of activities being described. The role of galectin-3 as adhesin for bacteria is based on its strong binding to lipopolysaccharides (LPSs), which brings the possibility of such a contamination in galectin preparations to awareness. This assumption was verified in three independent functional assay systems using polymyxin B as inhibitor of LPS-dependent effects. Moreover, a commercial LPS quantification kit also revealed LPS in galectin preparations. Chromatography was effective in removing LPS, suggesting that such a technique needs to be applied to prevent assigning cellular responses to galectins rather than LPS.

Human galectins as sensors for apoptosis/necrosis-associated surface changes of granulocytes and lymphocytes.

Changes in the glycomic profile can significantly affect the cells' communication with the environment. Plant lectins have so far been used to address the issue as to whether the courses of apoptosis or necrosis are associated with such alterations. We, here, initiate the study of members of the family of functionally pleiotropic human galectins in this respect. Established protocols for the induction of apoptosis/necrosis of blood cells and for flow cytometry using annexin V/propidium iodide were combined with cell surface staining using biotinylated galectins at a nontoxic concentration. The galectin panel covered members from all three subfamilies. Flow cytometry revealed specific binding of galectins to viable control cells and conspicuous staining differences when testing apoptotic or necrotic cells. Onset and especially progression of cell death led to pronounced reactivity with the proto-type galectins-1, -2, and -7 and tandem-repeat-type galectin-4. Extent of staining depended on the nature and stage of cell death, type of dying cell, and type of galectin. Galectins act as sensors for cell-death-associated surface changes. Staining of late-apoptotic polymorphonuclear cells was particularly strong. Examining the functional significance of this result may reveal a new aspect within the surveillance system to protect against autoinflammation.

Sweet clearance: involvement of cell surface glycans in the recognition of apoptotic cells.

Glycans cover the surfaces of all mammalian cells. Their structural variety provides enormous potential for information storage and transfer. According to the concept of the sugar code, they act as biochemical signals decoded by a large number of lectins which are defined as sugar binding proteins. The importance of glycan-lectin interaction in diverse immune system functions becomes increasingly apparent. Here, we review apoptotic cell clearance and especially focus on modifications of glycans on apoptotic cells.

Autoimmunity and chronic inflammation - two clearance-related steps in the etiopathogenesis of SLE.

Systemic lupus erythematosus (SLE) is an autoimmune disease with very prominent chronic inflammatory aspects that render into multiple symptoms and clinical signs. The precise etiology of SLE remains elusive; however, it is known that its etiopathogenesis is of multifactorial nature. The production of autoantibodies (AAb) targeting double stranded DNA (dsDNA) and other nuclear autoantigens is the main characteristic of this disease. These target antigens are often modified and/or translocated when apoptotic cells undergo secondary necrosis as a consequence of the clearance deficiency in patients with SLE. In healthy individuals, dead and dying cells are rapidly removed by macrophages in an anti-inflammatory context; this does not elicit immune responses. In SLE, apoptotic cells are often not properly cleared; autoantigens leak out, and are subsequently presented to B cells by follicular dendritic cells (FDC) in secondary lymphoid tissues. This defect challenges the peripheral self-tolerance. Autoreactive B cell activation and production of anti-nuclear AAb result as the first step in the etiopathogenesis of SLE. The second step is the formation of immune complexes (IC) with apoptotic cell-derived nuclear remnants either in situ or deposited in various tissues. Nucleic acid-containing IC may also be ingested by phagocytes, which subsequently produce pro-inflammatory cytokines. Both processes result in chronic organ and tissue damage, development and maintenance of the systemic autoimmune disease. In conclusion, clearance deficiency may contribute to SLE in two ways: first, in germinal centres it enables the affinity maturation of autoreactive B cells and second, in peripheral tissues it leads to the accumulation of accessible nuclear autoantigens. Chronic inflammation in SLE is consequently promoted by the persistently binding of AAb with their cognate autoantigens forming a binary weapon: the nucleic acid-containing IC.

Sodium and potassium urate crystals differ in their inflammatory potential.

Uric acid (UA) is identified as a danger signal released from dying cells. It precipitates in sodium-rich extracellular fluid and in potassium-rich intracellular fluid as monosodium urate (MSU) and monopotassium urate (MPU), respectively. Here, we examined the structural and functional features of these crystals. In contrast to MPU MSU crystals induced reactive oxygen species production and release of pro-inflammatory cytokines in whole blood ex vivo assays. These results show that the cation of urate crystals determines the response of innate immune cells, indicating that the micromilieu at the site of crystal formation is important for their inflammatory potential.

Role of apoptosis failure in etiopathogenesis of systemic lupus erythematosus and murine lupus.

Apoptosis serves many functions in the homeostasis of multicellular organisms. Defects in apoptosis may lead to clonal expansion and accumulation of autoreactive lymphocytes, which may result in the rare human autoimmune lymphoproliferative syndrome, a mild autoimmune reaction against cells in the blood. Defects in the clearance of apoptotic cells lead to accumulation of dying cells, which may enter later stages of cell death and release their contents, thereby critically contributing to the etiopathogenesis of the autoimmune disease systemic lupus erythematosus. For an efficient therapy of systemic lupus erythematosus, it is necessary to analyze apoptosis and clearance defects and to unravel factors leading to its onset.