Galectins: major signaling modulators inside and outside the cell.

Galectins control cell behavior by acting on different signaling pathways. Most of the biological activities ascribed to these molecules rely upon recognition of extracellular glycoconjugates and establishment of multivalente interactions, which trigger adaptive biological responses. However, galectins are also detected within the cell in different compartments, where their regulatory functions still remain poorly understood. A deeper understanding of the entire galectin signalosome and its impact in cell behavior is therefore essential in order to delineate new strategies to specifically manipulate both galectin expression and function. This review summarizes our current knowledge of the signaling pathways activated by galectins, their glycan dependence and the cellular compartment where they become activated and are biologically relevant.

Nucleosomes inhibit phagocytosis of apoptotic thymocytes by peritoneal macrophages from MRL+/+ lupus-prone mice.

The nucleosome, the basic structure of chromatin and normal product of cell apoptosis, plays a pivotal role both in the induction and the pathogenesis of systemic lupus erythematosus (SLE). Nucleosomes have been found to circulate at high levels in patients with SLE and apoptosis of lymphoid cells is increased during human and murine lupus. In this study, we examined the presence of possible defects in clearance mechanisms of apoptotic cells in murine lupus, and questioned further whether nucleosomes could compromise this phagocytic process. There did not appear to be any intrinsic functional defect of macrophages from young MRL+/+ lupus-prone mice to recognize and phagocytose apoptotic thymocytes. Nucleosomes, as a mimic of increased cell apoptotsis in vivo, induced a strong, dose-dependent, inhibition of phagocytosis of apoptotic thymocytes by young, pre-autoimmune, macrophages of MRL+/+ mice, whereas macrophages of non-autoimmune C3H mice only exhibited a trend to inhibition. The nucleosome-elicited inhibitory effect persisted during the development of the autoimmune response and appeared to be specific for the molecular mechanisms involved in macrophage phagocytosis of apoptotic cells. Our data suggest that nucleosome elicited inhibition of phagocytosis of apoptotic cells by MRL+/+ macrophages before the onset of the autoimmune response contribute, in a positive loop, to sustain and/or augment the levels of circulating (and potentially immunogenic) nucleosomes in lupus.

Isolation and characterization of apoptotic nucleosomes, free and complexed with lupus autoantibody generated during hybridoma B-cell apoptosis.

Increasing evidence suggests that immune complexes made of anti-nuclear antibodies bound to nucleosomes released from dead cells play an important role in the pathogenesis of lupus nephritis. However, the nature and composition of apoptotic nucleosomes still remain elusive. Since large amounts of nucleosomes are released from cells undergoing apoptosis in hybridoma cell cultures, we used hybridomas secreting anti-DNA and anti-nucleosome antibodies grown in protein-free medium to generate nucleosome/anti-DNA and /anti-nucleosome immune complexes, as well as an irrelevant antibody hybridoma to generate free, non-complexed apoptotic nucleosomes. Hybridoma supernatants were fractionated by size-exclusion gel chromatography and eluted fractions with a ratio of A260/A280 >1.2 were pooled and analysed for DNA and histone profiles by gel electrophoresis and immunoblotting. When run on a 'native' gel, 'intact' apoptotic nucleosomes, free or within anti-nucleosome immune complexes, showed a strikingly reduced size compared with 'standard' nucleosomes prepared in vitro by endonuclease digestion of cell nuclei. Nucleosomal DNA (extracted from either free or complexed apoptotic nucleosomes) appeared as a major band of 160-180 bp, and had the size of 'standard' mononucleosome DNA, suggesting degradation of the histone moiety of apoptotic nucleosomes. Histone immunoblotting revealed degradation of histones H3 and H4, which was dramatically enhanced when apoptotic nucleosomes were complexed with an anti-nucleosome antibody. Our results provide direct evidence for abnormal histone composition of apoptotic nucleosomes and suggest that the fine specificity of the complexing antibody has an influence on complexed nucleosome composition.

Trypanosoma cruzi: the major cysteinyl proteinase (cruzipain) is a relevant immunogen of parasite acidic antigens (FIII).

This study examined the immune responses induced by cruzipain, a well-characterized T. cruzi antigen, to determine whether it is a relevant immunogen among the parasite acidic antigens (FIII), for which some biological properties have been studied previously. Humoral and cellular immune responses were investigated in BALB/C mice after immunization with cruzipain or FIII. Skin tests revealed immediate type-hypersensitivity (ITH) and delayed-type hypersensitivity (DTH) reactions to cruzipain in both groups of immunized mice. IgG1 and IgE isotypes against cruzipain were detected by ELISA in both groups and immunoblot studies showed that these antibodies recognized a major protein band of 50 kDa, cruzipain. The antigen-specific proliferative responses of spleen lymphocytes from both groups of immunized mice were also increased. Immunization with cruzipain of FIII antigen significantly enhanced the percentage survival of mice challenged with 10(3) trypomastigotes. The results revealed high cross-reactivity between cruzipain and FIII, suggesting the cruzipain is a relevant immunogen among the parasite acidic antigens.

Trypanosoma cruzi: immunological cross-reactivity of the major cysteinyl proteinase (cruzipain) with a parasite cytosol acidic antigen (FIV).

This paper shows that a polyclonal monospecific rabbit antiserum to cruzipain, the major T. cruzi cystein proteinase, cross-reacts with a cytosol acidic antigen (F IV) isolated from the epimastigote stage of the same parasite. In addition, antibodies specific for F IV purified from chagasic patient sera or murine anti F IV sera, also react with cruzipain. This was demonstrated by ELISA, DOT-ELISA, native and electrophoretic Immunoblot. These findings suggest that F IV contains an antigen immunologically cross-reactive with cruzipain.