Lectin-binding Receptors Research Articles

Spleen Tyrosine Kinase Is a Critical Regulator of Neutrophil Responses to Candida Species.

Invasive fungal infections constitute a lethal threat, with patient mortality as high as 90%. The incidence of invasive fungal infections is increasing, especially in the setting of patients receiving immunomodulatory agents, chemotherapy, or immunosuppressive medications following solid-organ or bone marrow transplantation. In addition, inhibitors of spleen tyrosine kinase (Syk) have been recently developed for the treatment of patients with refractory autoimmune and hematologic indications. Neutrophils are the initial innate cellular responders to many types of pathogens, including invasive fungi. A central process governing neutrophil recognition of fungi is through lectin binding receptors, many of which rely on Syk for cellular activation. We previously demonstrated that Syk activation is essential for cellular activation, phagosomal maturation, and elimination of phagocytosed fungal pathogens in macrophages. Here, we used combined genetic and chemical inhibitor approaches to evaluate the importance of Syk in the response of neutrophils to Candida species. We took advantage of a Cas9-expressing neutrophil progenitor cell line to generate isogenic wild-type and Syk-deficient neutrophils. Syk-deficient neutrophils are unable to control the human pathogens Candida albicans, Candida glabrata, and Candida auris Neutrophil responses to Candida species, including the production of reactive oxygen species and of cytokines such as tumor necrosis factor alpha (TNF-α), the formation of neutrophil extracellular traps (NETs), phagocytosis, and neutrophil swarming, appear to be critically dependent on Syk. These results demonstrate an essential role for Syk in neutrophil responses to Candida species and raise concern for increased fungal infections with the development of Syk-modulating therapeutics.IMPORTANCE Neutrophils are recognized to represent significant immune cell mediators for the clearance and elimination of the human-pathogenic fungal pathogen Candida The sensing of fungi by innate cells is performed, in part, through lectin receptor recognition of cell wall components and downstream cellular activation by signaling components, including spleen tyrosine kinase (Syk). While the essential role of Syk in macrophages and dendritic cells is clear, there remains uncertainty with respect to its contribution in neutrophils. In this study, we demonstrated that Syk is critical for multiple cellular functions in neutrophils responding to major human-pathogenic Candida species. These data not only demonstrate the vital nature of Syk with respect to the control of fungi by neutrophils but also warn of the potential infectious complications arising from the recent clinical development of novel Syk inhibitors for hematologic and autoimmune disorders.

Migration of Fasciola hepatica newly excysted juveniles is inhibited by high-mannose and oligomannose-type N-glycan-binding lectins.

Fasciola hepatica has both zoonotic importance and high economic impact in livestock worldwide. After ingestion by the definitive host, the Newly Excysted Juveniles (NEJ) penetrate the intestine before reaching the peritoneal cavity. The role of some NEJ-derived proteins in invasion has been documented, but the role of NEJ glycans or lectin-binding receptors during initial infection in the gut is still unknown. To address these questions, the migration of NEJ through rat intestine was recorded at 30 min intervals up to 150 min by two ex vivo methods. Firstly, jejunal sheets were challenged with NEJ incubated with biotinylated lectins. Secondly, untreated NEJ were incubated with distal jejunum pre-treated with lectins. Both Concanavalin A (ConA) and Galanthus nivalis (GNL), which recognize mannose-type N-glycans, significantly inhibited NEJ migration across the jejunum. Most of the lectins bound to the tegument and oral sucker of the NEJ, but only ConA and GNL maintained this interaction over 150 min. None of the lectins examined significantly reduced NEJ migration when pre-incubated with jejunal sheets, suggesting that host glycans might not be essential for initial binding/recognition of the gut by NEJ. Agents capable of blocking mannose-type N-glycans on the NEJ tegument may have potential for disrupting infection.

Plant‐insect interactions: what can we learn from plant lectins?

Many plant lectins have high anti-insect potential. Although the effects of most lectins are only moderately influencing development or population growth of the insect, some lectins have strong insecticidal properties. In addition, some studies report a deterrent activity towards feeding and oviposition behavior. Transmission of plant lectins to the next trophic level has been investigated for several tritrophic interactions. Effects of lectins with different sugar specificities can vary substantially with the insect species under investigation and with the experimental setup. Lectin binding in the insect is an essential step in exerting a toxic effect. Attempts have been made to study the interactions of lectins in several insect tissues and to identify lectin-binding receptors. Ingested lectins generally bind to parts of the insect gut. Furthermore, some lectins such as the Galanthus nivalus agglutinin (GNA) cross the gut epithelium into the hemolymph and other tissues. Recently, several candidate lectin-binding receptors have been isolated from midgut extracts. To date little is known about the exact mechanism for insecticidal activity of plant lectins. However, insect glycobiology is an emerging research field and the recent technological advances in the analysis of lectin carbohydrate specificities and insect glycobiology will certainly lead to new insights in the interactions between plant lectins and insects, and to a better understanding of the molecular mechanisms involved.

Uterine involution and endometrial function in postpartum pony mares

To determine endometrial regeneration in postpartum mares by analysis of histologic features, apoptosis and cell proliferation markers, lectin binding, cytokines, and progesterone and estrogen receptors in endometrial biopsy specimens. 9 postpartum mares. Mares were examined on postpartum days 1, 9, and 16, and uterine biopsy specimens were obtained for histologic examination. Lectin binding was analyzed histochemically, and expressions of Ki-67 antigen (proliferation marker), lysozyme, and caspase 3 (apoptosis marker) were studied immunohistochemically. Gene expressions for cytokines (interleukin-1beta, -6 and -8 and tumor necrosis factor-alpha), cyclooxygenase 2, prostaglandin-E-synthase, and estrogen and progesterone receptors were determined by use of quantitative real-time PCR assay. On day 1, neutrophils predominated but by day 9 had largely been replaced by lymphocytes and macrophages. High numbers of cells with staining for caspase 3 were found on day 1, but numbers decreased by day 9. In contrast, the number of cells with staining for Kiel 67 antigen increased between days 1 and 9. Lectin binding to the endometrium changed over time. Relative mRNA expressions for cytokines and prostaglandin-E-synthase did not differ among days. Expressions of progesterone and estrogen receptors were minimal on day 1 and increased by day 9. Early postpartum endometrial cells underwent apoptosis, but during the second week, postpartum proliferation of cells predominated. Lectin binding reflected changes in endometrial glycocalyx patterns. Increased expression of estrogen receptors allowed the endometrium to respond to estrogen during foal heat, and in subsequent diestrus, the endometrium was able to respond to progesterone.

Melanosome transfer to and translocation in the keratinocyte.

Complexion coloration in humans is primarily regulated by the amount and type of melanin synthesized by the epidermal melanocyte. However, additional and equally contributing factors consist of (1) efficient transfer of melanin from the melanocytes to the neighboring keratinocytes and (2) distribution and degradation of the transferred melanosomes by the recipient keratinocytes. Once synthesized in the cell body of the epidermal melanocyte, pigmented melanosomes are translocated down the dendrites and captured at the dendritic tips via various cytoskeletal elements. Molecules recently identified that participate in this process consist of Rab27a, myosin-Va and melanophilin. Eventually, these peripherally localized melanosomes are transferred to keratinocytes by a presently undefined mechanism. The protease-activated receptor-2 (PAR-2) and unidentified surface lectins and glycoproteins facilitate this transfer process. Once incorporated into the keratinocytes, melanosomes are distributed individually or as clusters, aggregated towards the apical pole of the nucleus, and degraded as the keratinocytes undergo terminal differentiation and desquamation. Ultraviolet irradiation (UVR) can modulate the process of melanosome transfer from the melanocytes to the keratinocytes. UVR can upregulate expression of PAR-2 and lectin-binding receptors and increase phagocytic activity of cultured keratinocytes. Therefore, many cellular and molecular events that occur after melanogenesis contribute to skin color.

Differential reactivities of the Arachis hypogaea (peanut) and Vicia villosa B4 lectins with human ovarian carcinoma cells, grown either in vitro or in vivo xenograft model

PNA and VVA B4 recognize the tumor-associated T antigen and its immediate precursor Tn, respectively. We found that both lectins are highly reactive in vitro, with human ovarian carcinoma cell lines, but only VVA B4 bound significantly to breast and oral cancer cells. This binding is inhibited by specific monosaccharides. The lectin binding receptors were purified, revealing a glycoprotein of 32 kDa for PNA, and two glycoproteins of 35 and 38 kDa for VVA B4. In vivo localization of PNA was almost exclusive (except for the kidneys) to the ovarian tumor xenografts. VVA B4 showed wider tissue biodistribution being preferentially accumulated in the tumors and ovaries.

Cytochemical study of the germinal membrane of the Echinococcus granulosus cyst

The present cytochemical study was undertaken to provide more information on the localization of enzymatic and glycoconjugates in the germinal membrane of the Echinococcus granulosus cyst. The distinctive distribution of binding sites for two lectins (peanut agglutinin and Dilochos biflorus agglutinin) in the germinal membrane are described. An investigation is made of the distribution and specific activity of adenosine triphhosphate, alkaline phosphatase and acid phosphatase. The results suggest that cells located in the deeper layer of the germinal membrane are intrinsic in the cellular differentiation process. The dissimilares detected in both the enzymatic activity and the lectin-binding receptors could be associated with metacestode development or degeneration.

Lectin-binding receptors, Na +,K +-ATPase, and acetylcholinesterase on immunocyte plasma membrane of Limulus polyphemus

Plasma membrane receptors are crucial for nonself tissue recognition. Using concanavalin A (Con A), wheat germ agglutinin, peanut agglutinin, soybean agglutinin (SBA), and winged pea agglutinin, five lectin-binding receptor molecules have been recognized on the plasma membrane of the granulocyte (immunocyte) of the horseshoe crab, Limulus polyphemus. Only Con A and SBA caused capping of surface receptors. On the basis of the known functions of these lectin-binding receptor molecules in other invertebrates and vertebrates, their roles in phagocytosis, encapsulation, signaling, and possibly in complement pathway activation are postulated. In addition to lectin-binding receptors, Na +,K +-ATPase and acetylcholinesterase were detected on the plasma membrane. Because Limulus dates back to some 200 million years, the antiquity of these molecules is suggested. Furthermore, some of the lectin-binding surface receptors have the potential to be used as markers to separate different kinds of hemocytes in higher arthropods and to distinguish between normal and neoplastic cells in humans.

Electrophoretic characterization of muscarinic receptors under denaturating and nondenaturating conditions: Computer-assisted Ferguson plot analysis

The physical properties of the covalently labeled ([ 3H]propylbenzilylcholine mustard) muscarinic acetylcholine receptor from rat brain were studied by sodium dodecyl sulfate-polyacrylamide electrophoresis and computer-assisted Ferguson plot analysis. No proteolytic degradation or dimerization of the ligand binding subunit was found. No clues for different molecular weight forms or anomalous migration of the muscarinic receptor were detected. The weighted regression analysis of Ferguson plots gave an apparent molecular mass of 64–65 kDa. A new method for the electrophoretic separation of native (quinuclidinyl[ 3H]benzilate labeled) muscarinic receptor-detergent complexes was used for the comparison of wheat germ agglutinin binding, and not lectin binding receptors which were obtained by selective solubilization from porcine striatum. For this purpose, the computer-assisted Ferguson plot analysis is particularly suitable, since it renders possible the statistical assessment of both size and charge differences. Both receptor-detergent complexes were found to differ; statistically significant in their net charge but not in their size. The data support the view that muscarinic receptors from different sources may differ considerably in their glycosylation and that the receptor from porcine striatum can reversibly associate with a low-molecular-mass component which contains sialic acid.

Effect of tinidazole on the cellular immune response.

A single 500 mg dose of tinidazole was given to fourteen healthy volunteers. Cellular immune functions were studied, before and 2 and 24 h after drug ingestion. Blast transformation of lymphocytes to Con-A was significantly lower (P less than 0.01) in samples obtained 2 h after ingestion. No significant changes were found in the other immunological parameters studied. We conclude that these findings could be caused by reversible blockage of lectin binding receptors on the lymphocyte surface.

Lectin binding and steroid receptors in human breast carcinomas.

A series of breast carcinomas of known steroid receptor status have been examined for evidence of binding of the lectins peanut agglutinin, soy bean agglutinin and wheat germ agglutinin. Correlations were found between oestrogen receptor status and reactivity of carcinomas to peanut agglutinin and soy bean agglutinin but these were not absolute. Wheat germ agglutinin binding was unrelated to the presence of oestrogen receptors. No relationship was evident between progestogen receptors and the binding of any lectin. It therefore seems unlikely that lectin histochemistry can replace steroid receptors as markers of hormone dependence in breast carcinomas.

Lectin binding properties of human follicular center lymphocytes and follicular (nodular) lymphomas.

The distribution of lectin binding receptors in normal human lymphoid tissue and follicular (nodular) lymphoma was studied in tissue sections using a panel of lectin-peroxidase and lectin-fluorescein conjugates: Concanavalin A (Con A), Peanut agglutinin (PNA), Lotus tetragonolobus agglutinin (LTA), Soybean agglutinin, Ulex europeus and Bandeiraea simplicifolia. Two lectins studied, PNA and LTA were found to bind selectively to the cell membranes of follicular centre lymphocytes in normal lymphoid tissue, and to the neoplastic cells of follicular (nodular) lymphomas. Con A, in contrast, bound selectively to follicular centre macrophages (tingible body cells) and identified in follicular (nodular) lymphomas a population of dendritic-like cells not otherwise recognized and possibly corresponding to dendritic cells identified ultrastructurally. Follicular (nodular) lymphomas share the lectin binding properties of non-neoplastic follicular centres. The expression of receptors for lectins with blood group activity (PNA T-like, LTA H-like) on follicular lymphocytes may play a role in follicle formation.

Neoplastic cells as targets of spontaneously cytotoxic lymphocytes: studies with natural killer-like cell lines.

Native natural killer (NK) cells comprise a heterogeneous family of lymphocytes distributed among several organs, which display spontaneous cytotoxic reactions directed against a broad range of tumor targets. In these studies, murine cell lines have been established in vitro following the selective expansion of bone marrow- and spleen-derived killer progenitors in culture medium supplemented with interleukin-2. Several clones of independent origin have been characterized in order to determine the extent of their phenotypic and functional diversity. With few exceptions most of them were found to be highly effective in lysing a variety of tumor cell lines, to share common cell surface alloantigens, lectin-binding receptors, and cytochemical markers. The presence of prominent azurophilic cytoplasmic granules is the most characteristic ultrastructural feature of these cells. In attempting to elucidate the nature of membrane components specifically recognized by NK cells we compared several isogenic tumor cell variants selected on the basis of their differential NK susceptibility, immunogenicity, metastatic potential or resistance to cytotoxic plant lectins. Sialylated glycoconjugates exposed on the external face of the tumor cell membrane appear to be essential determinants in the interaction between NK cells and their targets. Permanent cell lines retaining most of the functional attributes of endogenous NK cells may prove instrumental in understanding their role during tumor progression.

Surface properties of extracellular malaria parasites: electrophoretic and lectin-binding characteristics.

The surface charge and lectin-binding capacity of isolated malaria parasites and host erythrocytes were analyzed and compared by chromatographic, electrophoretic, and cytochemical methods. Results indicated that at physiological pH values both freshly prepared and glutaraldehyde-fixed parasites and erythrocytes possess a net negative surface charge. Both cell types were strongly bound to cation-exchange resins and underwent cathode-directed electrophoretic migration. The isoelectric points for erythrocyte-free parasites and uninfected erythrocytes were approximately 3.0 and 4.0, respectively. The different effects of selective enzymatic digestion and solvent extraction on the electrophoretic mobilities of free parasites and erythrocytes suggested that the chemical constituents responsibile for the net negative surface charges on each type of cell are different. The surface charge of the free parasites seemed mainly to be a function of ionized phospholipids rather than of the ionogenic sialic acid moieties, which are the major contributors to the negative charge on erythrocytes. Results of lectin-binding studies indicated that specific glycosidimoieties (i.e., glucose, galactose, mannose, and n-acetyglucosamine), common to the erythrocyte surface, were either absent or in low concentration at the parasite's surface. These observations suggest that the normally intracellular malaria parasites have surface characteristics, differing from those of the host cell, characterized by a scarcity of lectin-binding receptors and sialic acid residues and by the major contribution of lipids to their surface charge.

Biosynthesis in vitro and the pattern of lectin binding receptors in monkey kidney cell surfaces

The glycosyltransferase activities involved in the biosynthesis in vitro of neutral blood group-related glycosphingolipids were measured in African green monkey kidney cells (Vero) grown in culture. The a-fucosyltransferases which catalyzed the reaction between GDP-fucose and corresponding acceptors to form H-active and novel Le a-type glycosphingolipids were characterized in membrane fractions isolated from Vero cells and monkey bone marrow. Using 125I-labeled Ulex europeus and Lotus tetragonolobus lectins the differential binding to Vero cell surface glycoproteins and glycolipids was studied under various conditions.