Immune escape through C-type lectins on dendritic cells

Dendritic cells (DCs) detect different pathogens and elicit tailored anti-microbial immune responses. They express C-type lectins that recognise carbohydrate profiles on microorganisms, resulting in internalisation, processing and presentation. Intracellular sequences of distinct DC-specific lectins point to differences in intracellular routing that influence antigen presentation. Moreover, putative signalling motifs hint to the activation of DCs on carbohydrate recognition. Recent evidence shows that not only pathogens, but also tumour antigens, exploit C-type lectins to escape intracellular degradation resulting in abortive immunity. More insight into ligand specificity, intracellular targeting and signalling will reveal the pathways by which pathogens modulate immunity through C-type lectins.     

Carbohydrate specificities of the murine DC-SIGN homologue mSIGNR1

C-type lectins are important receptors expressed by antigen presenting cells that are involved in cellular communications as well as in pathogen uptake. An important C-type lectin family is represented by DC-SIGN and its homologues in human and mouse. Here we have investigated the carbohydrate specificity of cellular mSIGNR1 and compared it with DC-SIGN and L-SIGN. mSIGNR1 has a similar specificity as human DC-SIGN for high mannose-containing ligands present on both cellular and pathogen ligands. However, the DC-SIGN molecules differ in their recognition of Lewis antigens; mSIGNR1 interacts not only with Le(x/y) and Le(a/b) antigens similar to DC-SIGN, but also with sialylated Lex, a ligand for selectins. The differential recognition of Lewis antigens suggests differences between mSIGNR1 and DC-SIGN in the recognition of cellular ligands and pathogens that express Lewis epitopes.     

Identification of the reactive subunits of Aspergillus umbrosus involved in the antigenic response in farmer's lung

Background Farmer's lung (FL) is the most common form of extrinsic allergic alveolitis and the fungus Aspergillus umbrosus has frequently been associated with FL among Finnish farmers. IgG and IgA class antibodies against Aspergillus umbrosus are found in the serum of FL patients and healthy exposed farmers. So far the immunologically reactive subunits of Aspergillus umbrosus are unknown. Objectives The purpose of the study was to identify and localize the reactive subunits of Aspergillus umbrosus that are involved in the antigenic response in FL. Methods The distribution of the primary antibody on the outer wall layers of 4- and 11 day-old fungi Aspergillus umbrosus was studied by pre-embedding immunolabelling with fluorescein isothiocyanate (FITC)- and gold-conjugated antibodies. The surface carbohydrates of the outer wall layers were studied using FITC-conjugated lectins. Results FITC-conjugated antibodies from FL patient sera reacted with spores (conidia), phialides and hyphae, whereas the fruiting body, cleistothecia, remained unstainable. Immunofluorescence labelling was confirmed by immunolabelling electron microscopy, and gold-conjugated IgG antibodies were found on the outer cell walls of spinulose conidia, and in a less degree on the outer cell walls of hyphae and phialides. Only single gold particles were found scattered on the surfaces of cleistothecia. The surface carbohydrates of Aspergillus umbrosus conidia. vesicles, phialides and hyphae had a high affinity to GlcNAcβl- and Manαl-/Glcαl- specific lectins and only GlcNAcβl-specific lectins also reacted with the outer cell walls of cleistothecia. Blocking of the antigenic sites of Aspergillus umbrosus by preincubating antigen-coated enzyme linked immunosorbent assay (FLISA) plates with lectins caused some inhibition, indicating that sites with the highest affinity for lectins were not always antigenic sites. Conclusion Gold- and FITC-conjugated antibodies were distributed mostly on the outer wall layers of conidia, hyphae and phialides of Aspergillus umbrosus and GlcN Acβl -linked lectins had the strongest affinity to the outer wall layers.     

The target antigens of naturally occurring human anti-beta-galactose IgG are cryptic on porcine aortic endothelial cells

Abstract: The identification of the xeno‐antigens/xeno‐antibodies combinations involved in pig‐to‐human xenograft rejection is an essential step for understanding this process and for the development of procedures to prevent it. Although it is widely accepted that the terminal disaccharide Galα1,3Gal‐R is by far the major epitope recognized by human natural antibodies reactive with pig tissues, there is also evidence that other carbohydrates epitopes might be important in xenograft rejection.
In an attempt to further improve our knowledge of the repertoire of human natural antibodies with anti‐pig specificity we sought to determine whether naturally occurring human anti‐β‐galactose IgG could interact with porcine aortic endothelial cells (PAEC). Histochemical analysis of porcine aorta sections revealed that the carbohydrate structures recognized by the anti‐β‐galalactose IgG are present on endothelial cells but in a cryptic form that can be unmasked by sialidase treatment. These structures were also found to be cryptic in cultured PAEC. In addition we demonstrated that PAEC may adsorb fetal calf serum (FCS) glycoproteins when cultured in FCS‐supplemented medium, a process susceptible to generating artifactual observations in carbohydrate antigens analysis.
In conclusion, despite their abundance, human anti‐β‐galactose IgG do not represent a primary concern in pig‐to‐human xenotransplantation as the carbohydrate structures to which they bind are normally masked by sialic acid residues on porcine endothelial cells. However, whether these cryptic epitopes might be exposed on endothelial cells from genetically engineered animals should be further investigated because, if so, additional approaches will be needed to suppress their interaction with human anti‐β‐galactose IgG.     

SPECIFICITY OF HEMATOPOIETIC STEM CELL HOMING

Homing of hematopoietic stem cells (HSC) may be defined as the cells’ ability to seek marrow stroma selectively, to interact with it and subsequently to lodge within it to initiate hematopoiesis. This complex process is no doubt mediated through multiple recognition/adhesion events. Homing may proceed through one of several alternative mechanisms, however, such as through physical trapping of stem cells by marrow ultrastructural elements or through the providing of a selective survival and/or proliferative advantage by marrow. A third alternative that provides for the central element of stem cell homing—its high degree of specificity—is through the action of a specific homing protein in HSC. There are data to support this latter mechanism of stem cell homing as the correct one, and the nature of this protein may be similar to that of the lymphocyte homing receptors that are lectin-like molecules. Lectin–carbohydrate interactions are known to provide enormous specificity to cell recognition processes and to participate in cellular targeting. Leukemic cells have recently been demonstrated to home to marrow stroma and proliferate in the same way as normal stem cells. Thus, identification of proteins or other adhesion molecules that participate in normal and malignant cell homing could lead to more specific recruitment regimens for tumour-free collections.     

豆类凝集素FRIL通过调控细胞周期分子的表达维持造血干/祖细胞的静息

目的从细胞周期角度探讨豆类凝集素 FRIL(Flt3 receptor-interacting lectin)体外维持造血干/祖细胞静息的分子机制。方法以添加 FRIL、Flt3配体(FL)和不添加因子的培养基分别培养脐血 CD34~ 细胞,采用 RT-PCR 和 Western blot 法分别从 mRNA 和蛋白水平检测细胞周期相关分子的表达。结果新分离的 CD34~ 细胞中未检测到 G_0/G_1期相关 Cyclin 和 CDK 蛋白的表达,培养3d 时FRIL 组 CyclinD3、CDK6蛋白相对表达量(分别为483±63、553±39)低于两个对照组(FL 组:2437±52、3209±98;空白对照组:914±105、1497±55);培养3 d 时 FRIL 组 P27蛋白相对表达量(0.312±0.030)低于对照组(FL 组:0.787±0.024;空白对照组:0.616±0.029),但表达较高的 P53蛋白(FRIL组、FL 组、空白对照组分别为4.476±0.159、0.581±0.099、2.167±0.114)。FRIL 组细胞周期正向调节因子的 mRNA 相对表达量低于或相当于 FL 组和空白对照组。结论 FRIL 通过抑制参与造血细胞周期调控的 CyclinD3和 CDK6的表达,延迟了造血干/祖细胞的细胞周期,P27在 FRIL 抑制造血干/祖细胞分化中发挥了重要作用,P53也参与了 FRIL 对造血干/祖细胞的维持作用。     

胆囊癌内分泌细胞嗜银染色及免疫组化研究

应用嗜银染色和免疫组化技术研究胆囊癌组织中内分泌细胞及其意义。４０例胆囊癌嗜银染色阳性者１０例，均为女性，７例发生癌转移，７例伴胆囊结石。免疫组化结果表明：嗜银染色阳性者，免疫组化多为阳性，其中ＥＭＡ，ＣＥＡ，ＨＣＧ阳性各７例；ＰＮＡ，ＣｏｎＡ，ＳＭ各５例；ＧＮ４例。结果提示部分胆囊癌病例内分泌细胞染色阳性，且阳性病例可能预后不良。