Use of the avidin-biotin complex for specific staining of biological membranes in electron microscopy

A Rapid and Simplified Method to Isolate Specific Regulators Based on Biotin-Avidin Binding Affinities in Crops

Transcription factors (TFs) are indispensable components of transcriptional regulatory pathways involved in crop growth and development. Herein, we developed a new method for the identification of upstream TFs specific to genes in crops based on the binding affinities of biotin and avidin. First, we constructed and verified the new biotin and avidin system (BAS) by a coprecipitation assay. Subsequently, the feasibility of DNA-based BAS (DBAS) was further proved by in vivo and in vitro assays. Furthermore, we cloned the promoter of rice OsNRT1.1B and the possible regulators were screened and identified. Additionally, partial candidates were validated by the electrophoresis mobility shift assay (EMSA), yeast one-hybrid, and luciferase activity assays. Remarkably, the results showed that the candidates PIP3 and PIP19 both responded to nitrate immediately and overexpression of PIP3 caused retard growth, which indicates that the candidates are functional and the new DBAS method is useful to isolate regulators in crops.

Copper radical oxidases: galactose oxidase, glyoxal oxidase, and beyond!

The copper radical oxidases (CROs) are an evolutionary and functionally diverse group of enzymes established by the historically significant galactose 6-oxidase and glyoxal oxidase from fungi. Inducted in 2013, CROs now constitute Auxiliary Activity Family 5 (AA5) in the Carbohydrate-Active Enzymes (CAZy) classification. CROs catalyse the two-electron oxidation of their substrates using oxygen as the final electron acceptor and are particularly distinguished by a cross-linked tyrosine-cysteine co-factor that is integral to radical stabilization. Recently, there has been a significant increase in the biochemically and structurally characterized CROs, which has revealed an expanded natural diversity of catalytic activities in the family. This review provides a brief historical introduction to CRO biochemistry and structural biology as a foundation for an update on current advances in CRO enzymology, biotechnology, and biology across kingdoms of life.

Active-Site Engineering Switches Carbohydrate Regiospecificity in a Fungal Copper Radical Oxidase

Copper radical oxidases (CROs) from Auxiliary Activity Family 5, Subfamily 2 (AA5_2), are organic cofactor-free biocatalysts for the selective oxidation of alcohols to the corresponding aldehydes. AA5_2 CROs comprise canonical galactose-6-oxidases as well as the more recently discovered general alcohol oxidases and aryl alcohol oxidases. Guided by primary and tertiary protein structural analyses, we targeted a distinct extended loop in the active site of a Colletotrichum graminicola aryl alcohol oxidase (CgrAAO) to explore its effect on catalysis in the broader context of AA5_2. Deletion of this loop, which is bracketed by a conserved disulfide bridge, significantly reduced the inherent activity of the enzyme toward extended galacto-oligosaccharides, as anticipated from molecular modeling. Unexpectedly, kinetic and product analysis on a range of monosaccharides and disaccharides revealed that an altered carbohydrate specificity in CgrAAO-Δloop was accompanied by a complete change in regiospecificity from C-6 to C-1 oxidation, thereby generating aldonic acids. C-1 regiospecificity is unprecedented in AA5 enzymes and is classically associated with flavin-dependent carbohydrate oxidases of Auxiliary Activity Family 3. Thus, this work further highlights the catalytic adaptability of the unique mononuclear copper radical active site and provides a basis for the design of improved biocatalysts for diverse potential applications.

A survey of substrate specificity among Auxiliary Activity Family 5 copper radical oxidases

There is significant contemporary interest in the application of enzymes to replace or augment chemical reagents toward the development of more environmentally sound and sustainable processes. In particular, copper radical oxidases (CRO) from Auxiliary Activity Family 5 Subfamily 2 (AA5_2) are attractive, organic cofactor-free catalysts for the chemoselective oxidation of alcohols to the corresponding aldehydes. These enzymes were first defined by the archetypal galactose-6-oxidase (GalOx, EC 1.1.3.13) from the fungus Fusarium graminearum. The recent discovery of specific alcohol oxidases (EC 1.1.3.7) and aryl alcohol oxidases (EC 1.1.3.47) within AA5_2 has indicated a potentially broad substrate scope among fungal CROs. However, only relatively few AA5_2 members have been characterized to date. Guided by sequence similarity network and phylogenetic analysis, twelve AA5_2 homologs have been recombinantly produced and biochemically characterized in the present study. As defined by their predominant activities, these comprise four galactose 6-oxidases, two raffinose oxidases, four broad-specificity primary alcohol oxidases, and two non-carbohydrate alcohol oxidases. Of particular relevance to applications in biomass valorization, detailed product analysis revealed that two CROs produce the bioplastics monomer furan-2,5-dicarboxylic acid (FDCA) directly from 5-hydroxymethylfurfural (HMF). Furthermore, several CROs could desymmetrize glycerol (a by-product of the biodiesel industry) to D- or L-glyceraldehyde. This study furthers our understanding of CROs by doubling the number of characterized AA5_2 members, which may find future applications as biocatalysts in diverse processes.

Two Fusarium copper radical oxidases with high activity on aryl alcohols

BACKGROUND

Biomass valorization has been suggested as a sustainable alternative to petroleum-based energy and commodities. In this context, the copper radical oxidases (CROs) from Auxiliary Activity Family 5/Subfamily 2 (AA5_2) are attractive biocatalysts for the selective oxidation of primary alcohols to aldehydes. Originally defined by the archetypal galactose 6-oxidase from Fusarium graminearum, fungal AA5_2 members have recently been shown to comprise a wide range of specificities for aromatic, aliphatic and furan-based alcohols. This suggests a broader substrate scope of native CROs for applications. However, only 10% of the annotated AA5_2 members have been characterized to date.

RESULTS

Here, we define two homologues from the filamentous fungi Fusarium graminearum and F. oxysporum as predominant aryl alcohol oxidases (AAOs) through recombinant production in Pichia pastoris, detailed kinetic characterization, and enzyme product analysis. Despite possessing generally similar active-site architectures to the archetypal FgrGalOx, FgrAAO and FoxAAO have weak activity on carbohydrates, but instead efficiently oxidize specific aryl alcohols. Notably, both FgrAAO and FoxAAO oxidize hydroxymethyl furfural (HMF) directly to 5-formyl-2-furoic acid (FFCA), and desymmetrize the bioproduct glycerol to the uncommon L-isomer of glyceraldehyde.

CONCLUSIONS

This work expands understanding of the catalytic diversity of CRO from AA5_2 to include unique representatives from Fusarium species that depart from the well-known galactose 6-oxidase activity of this family. Detailed enzymological analysis highlights the potential biotechnological applications of these orthologs in the production of renewable plastic polymer precursors and other chemicals.

On the ultrastructural localization of cell surface sialyl residues versus anionic sites

Membrane-associated sialic acids(SA) are considered to have an important role in a variety of cell sur ace interactions. Visualization of SA sites and their ultrastructural quantitative evaluation have heverally been based on the coulombic interaction between anionic sites of sialyl carboxyl groups with polycationic,electron dense markers, e.g. colloidal ferric hydroxide or cationized ferritin(CF). We have recently demonstrated an alternative method, whereby periodate-induced biotinylation (PIB) of unfixed cells can be used for specific localization of SA in thin sections by ferritin-conjugated avidin (FAv). It was further shown that PIB does not affect the surface anionic charge, since the latter is still available to CF-staining. In order to determine the role of anionic sites on the distribution and configuration of cell surface sialoglycoproteins and or sialoglycolipids, we have compared the topographic distribution of attached FAv or CF particles on normal and pathological blood cells,following successive treatment with sodium periodate and biotin hydrazide.

Approaches to Resolve False Reporting in Neutralizing Antibody Assays Caused by Reagent Leaching from Affinity Capture Elution Solid Phase

Insufficient drug tolerance presents a major challenge in the development of neutralizing antibody (NAb) assays for biotherapeutics. Sample pre-treatment using solid-phase extraction with acid dissociation (SPEAD) is widely reported to improve drug tolerance. In this paper, a case study is presented in which SPEAD was used in conjunction with a competitive ligand binding NAb assay format. A significant degree of biotin-drug conjugate leaching was observed resulting in the reporting of both false positive and false negative results in NAb assay. Mitigation steps have been evaluated to address drug/biotin-drug conjugate leaching. These steps included assessment of the streptavidin-coated plate in conjunction with biotin-drug conjugates at various biotin molar challenge ratios (MCR). In addition, an alternative method based on covalent capture of the drug on an aldehyde-activated plate was assessed. Both approaches were compared for the degree of drug/biotin-drug conjugate leaching during the second elution step of the SPEAD procedure. Moreover, the impact of various conditions on the assay performance was assessed, including elution pH, sample incubation time, and biotin MCR. For the covalent drug capture method, capture conditions were evaluated. Optimized conditions in both streptavidin capture and covalent capture methods enabled a significant reduction of drug/biotin-drug conjugate leaching. A streptavidin high binding capacity approach using biotin-drug conjugate with a MCR of 50:1 was chosen as the optimal method yielding a NAb assay with a fit for purpose sensitivity (153 ng/mL) and a drug tolerance of up to 50 μg/mL with 500 ng/mL PC.

Effects of salazosulfapyridine on the profile of cell surface proteins, revealed by biotinylation of cell surface proteins and 2-dimentional electrophoresis

OBJECTIVE

We investigated effects of salazosulfapyridine (SASP) on the protein profile of cell surface (CS)-proteins of SW982, a human synovial sarcoma cell line, using biotinylation of CS-proteins and 2-dimensional fluorescence difference gel electrophoresis (2D-DIGE).

METHODS

SW982 cells were treated with SASP and its metabolites, sulfapyridine (SP) and 5-aminosalicylic acid (5ASA). Then the cells were treated with a membrane-impermeable biotinylating reagent. Biotinylated CS-proteins were isolated using NeutrAvidin-bound beads. CS-proteins affected by the drugs were detected by 2D-DIGE and subjected to mass spectrometry.

RESULTS

By the 2D-DIGE analysis, in total 576 spots were detected, 29 out of which showed more than ±1.5-fold different intensity in the SASP-, SP-, and 5ASA-treated cells, compared to non-treated cells (p < 0.05). Interestingly, 7 out of the 29 spots changed their intensity only by SASP and 17 spots changed their intensity only by SP. We identified 9 protein from 15 out of the 29 spots, most of which were evidenced to exist on the cell surface by flow cytometry.

CONCLUSION

We found novel effects of SASP and its metabolites on SW982 cells by the combination of biotinylation of cell surface proteins and 2D-DIGE analysis. These data would help understanding of anti-rheumatic actions of SASP. Furthermore, the combination would be a useful method for the analysis of CS-proteins in various conditions.

Kinetic controlled affinity labeling of target enzyme with thioester chemistry

High specificity has been an important feature in affinity labeling for target profiling. Especially, to label targets via rapidly progressing reactions with consumption of ligand (probe), high specificity of reaction with common functional groups of target protein should be achieved without reactions with similar groups of non-target proteins. Herein, we demonstrate the kinetic controlled affinity labeling of acyl CoA synthetase using a fatty acid analogue containing a phenylthioester linkage. High specificity was attained by accelerating the labeling rate in the binding pocket. This approach could be useful for profiling a series of target enzymes and transporters in signal transduction pathways.

Identification of Receptor Tyrosine Kinase Inhibitors Using Cell Surface Biotinylation and Affinity Isolation

The mammalian vascular endothelial growth factor receptor tyrosine kinases (VEGFRs) bind circulating growth factors and regulate the process of angiogenesis. The discovery of new small molecules that target the enzymatic activity of the VEGFR family as potential antiangiogenic drugs is of much commercial interest in the pharmaceutical sector. Here, we describe the use of a combined cell surface biotinylation and affinity isolation procedure to monitor ligand-stimulated VEGFR trafficking in endothelial cells, in which novel VEGFR inhibitors from chemical libraries can be identified by their ability to inhibit receptor internalization. Unlike a traditional cell-free enzyme activity assay, such a cell-based approach provides a physiologically relevant readout of inhibitor activity. In this example, we use the VEGF-A-VEGFR-2 axis and the well-characterized tyrosine kinase inhibitor sunitinib as a working model; however this technique is highly applicable for the identification of inhibitors to other receptor tyrosine kinases.

Electrical coupling between Aplysia bag cell neurons: characterization and role in synchronous firing

In neuroendocrine cells, hormone release often requires a collective burst of action potentials synchronized by gap junctions. This is the case for the electrically coupled bag cell neurons in the reproductive system of the marine snail, Aplysia californica. These neuroendocrine cells are found in two clusters, and fire a synchronous burst, called the afterdischarge, resulting in neuropeptide secretion and the triggering of ovulation. However, the physiology and pharmacology of the bag cell neuron electrical synapse are not completely understood. As such, we made dual whole cell recordings from pairs of electrically coupled cultured bag cell neurons. The junctional current was nonrectifying and not influenced by postsynaptic voltage. Furthermore, junctional conductance was voltage independent and, not surprisingly, strongly correlated with coupling coefficient magnitude. The electrical synapse also acted as a low-pass filter, although under certain conditions, electrotonic potentials evoked by presynaptic action potentials could drive postsynaptic spikes. If coupled neurons were stimulated to spike simultaneously, they presented a high degree of action potential synchrony compared with not-coupled neurons. The electrical synapse failed to pass various intracellular dyes, but was permeable to Cs(+), and could be inhibited by niflumic acid, meclofenamic acid, or 5-nitro-2-(3-phenylpropylamino)benzoic acid. Finally, extracellular and sharp-electrode recording from the intact bag cell neuron cluster showed that these pharmacological uncouplers disrupted both electrical coupling and afterdischarge generation in situ. Thus electrical synapses promote bag cell neuron firing synchrony and may allow for electrotonic spread of the burst through the network, ultimately contributing to propagation of the species.

Antibodies biotinylated using a synthetic Z-domain from protein A provide stringent in situ protein detection

Antibody-based protein profiling on a global scale using immunohistochemistry constitutes an emerging strategy for mapping of the human proteome, which is crucial for an increased understanding of biological processes in the cell. Immunohistochemistry is often performed indirectly using secondary antibodies for detection, with the benefit of signal amplification. Direct immunohistochemistry instead brings the advantage of multiplexing; however, it requires labeling of the primary antibody. Many antibody-labeling kits do not specifically target IgG and may therefore cause labeling of stabilizing proteins present in the antibody solution. A new conjugation method has been developed that utilizes a modified Z-domain of protein A (ZBPA) to specifically target the Fc part of antibodies. The aim of the present study was to compare the ZBPA conjugation method and a commercially available labeling kit, Lightning-Link, for in situ protein detection. Fourteen antibodies were biotinylated with each method and stained using immunohistochemistry. For all antibodies tested, ZBPA biotinylation resulted in distinct immunoreactivity without off-target staining, regardless of the presence of stabilizing proteins in the buffer, whereas the majority of the Lightning-Link biotinylated antibodies displayed a characteristic pattern of nonspecific staining. We conclude that biotinylated ZBPA domain provides a stringent method for antibody biotinylation, advantageous for in situ protein detection in tissues.

α-Oxo aldehyde or glyoxylyl group chemistry in peptide bioconjugation

Since the 1990s, α-oxo aldehyde or glyoxylic acid chemistry has inspired a vast array of synthetic tools for tailoring peptide or protein structures, for developing peptides endowed with novel physicochemical properties or biological functions, for assembling a large diversity of bioconjugates or hybrid materials, or for designing peptide-based micro or nanosystems. This past decade, important developments have enriched the α-oxo aldehyde synthetic tool box in peptide bioconjugation chemistry and explored novel applications. The aim of this review is to give a large overview of this creative field.

Glycoproteomics enabled by tagging sialic acid- or galactose-terminated glycans

In this paper, we present two complementary strategies for enrichment of glycoproteins on living cells that combine the desirable attributes of "robust enrichment" afforded by covalent-labeling techniques and "specificity for glycoproteins" typically provided by lectin or antibody affinity reagents. Our strategy involves the selective introduction of aldehydes either into sialic acids by periodate oxidation (periodate oxidation and aniline-catalyzed oxime ligation (PAL)) or into terminal galactose and N-acetylgalactosamine residues by galactose oxidase (galactose oxidase and aniline-catalyzed oxime ligation (GAL)), followed by aniline-catalyzed oxime ligation with aminooxy-biotin to biotinylate the glycans of glycoprotein subpopulations with high efficiency and cell viability. As expected, the two methods exhibit reciprocal tagging efficiencies when applied to fully sialylated cells compared with sialic acid-deficient cells. To assess the utility of these labeling methods for glycoproteomics, we enriched the PAL- and GAL-labeled (biotinylated) glycoproteome by adsorption onto immobilized streptavidin. Glycoprotein identities (IDs) and N-glycosylation site information were then obtained by liquid chromatography-tandem mass spectrometry on total tryptic peptides and on peptides subsequently released from N-glycans still bound to the beads using peptide N-glycosidase F. A total of 175 unique N-glycosylation sites were identified, belonging to 108 nonredundant glycoproteins. Of the 108 glycoproteins, 48 were identified by both methods of labeling and the remainder was identified using PAL on sialylated cells (40) or GAL on sialic acid-deficient cells (20). Our results demonstrate that PAL and GAL can be employed as complementary methods of chemical tagging for targeted proteomics of glycoprotein subpopulations and identification of glycosylation sites of proteins on cells with an altered sialylation status.

Immunolocalization of nitric oxide synthase isoforms in human archival and rat tissues, and cultured cells

Nitric oxide (NO) exerts important physiological and pathological roles in humans. The study of NO requires the immunolocalization of its synthesizing enzymes, neuronal, endothelial and inducible NO synthases (NOS). NOS are labile to formalin-fixation and paraffin-embedding, which are used to prepare human archival tissues. This lability has made NOS immunohistochemical studies difficult, and a detailed protocol is not yet available. We describe here a protocol for the immunolocalization of NOS isoforms in human archival cerebellum and non-nervous tissues, and in rat tissues and cultured cells. Neuronal NOS antigenicity in human archival and rat nervous tissue sections was microwave-retrieved in 50 mM Tris-HCl buffer, pH 9.5, for 20 min at 900 W. Neuronal NOS was expressed in stellate, basket, Purkinje and granule cells in human and rat cerebellum. Archival and frozen human cerebellar sections showed the same neuronal NOS staining pattern. Archival cerebellar sections not subjected to antigen retrieval stained weakly. Antigenicity of inducible NOS in human lung was best retrieved in 10 mM sodium citrate buffer, pH 6.0, for 15 min at 900 W. Inflammatory cells in a human lung tuberculoma were strongly stained by anti-inducible NOS antibody. Anti-endothelial NOS strongly stained kidney glomeruli. Cultured PC12 cells were strongly stained by anti-neuronal NOS without antigen retrieving. The present immunohistochemistry protocol is easy to perform, timeless, and suitable for the localization of NOS isoforms in nervous and non-nervous tissues, in human archival and rat tissues. It has been extensively used in our laboratory, and is also appropriate for other antigens.

Chemoselective ligation techniques: modern applications of time-honored chemistry

Chemoselective ligation techniques enable the selective modification of proteins and other biomolecules in dilute aqueous solution. Importantly, these reactions occur at or near physiological pH and are compatible with the complex array of functional groups commonly found in biological macromolecules including proteins, nucleotides, and carbohydrates, allowing conjugation reactions to be carried out on unprotected substrates. Recently, a growing number of reactions with established utility in synthetic organic chemistry have been shown to have surprising utility in the context of biological molecules in aqueous media. In this review we highlight several promising reactions that may have widespread applicability in the generation of new materials based on biological macromolecules.

Biotinylation of antibodies

Using the characteristic of a high-affinity complex between avidin and biotin, biotinylated antibodies have wide applications in various immunochemical assays, especially where signal amplification is required. A method is described here for the biotinylation of immunoglobulins. The procedure utilizes water-soluble succinimidyl ester of biotin that reacts with primary amines of the lysine residues or the amino terminus on the antibody to form amide bonds. The method is simple and specific and results in stable conjugates retaining full immunologic activity.

Immunoglobulin G receptors of intestinal brush borders from neonatal rats

Intestinal absorptive cells of the neonatal rat display on their brush border membranes receptors for immunoglobulin G (IgG) which function in selective transfer of maternal IgG. Our Scatchard analysis of [125I]IgG binding to isolated brush borders has corroborated the presence of two classes of specific binding sites (KA1 = 2.4 X 10(7) M-1 and KA2 = 3.7 X 10(5) M-1) and the increase in overall binding with decreased buffer concentration, as shown by Wallace & Rees 1980. However, our Scatchard analysis of binding at different buffer concentrations indicates that the only significant effect of lowered buffer concentration is to increase the number of low-affinity sites. Neither the number nor the affinity of the high-affinity sites is affected. Furthermore, brush borders from rats at 21 days have only the low-affinity sites and at this age the selective transfer of IgG has ceased. Morphological experiments with tracers for both light and electron microscopy suggest that the high-affinity sites correspond to the specific IgG receptors on the apical membrane. The majority of the low-affinity sites are found within the terminal web and are likely not to be involved in selective transport of IgG.

Detection of antigen specific B-cells in tissues

The role of B-cells and autoantibodies in tissue destructive events of autoimmune diseases is emerging, and thereby increasing interest in identifying the presence and location of autoreactive B-cells and autoantibody secreting plasma cells. For visualization and analysis of the autoreactive B-cells, the antigen of interest is selected and produced and purified from native or recombinant sources. Biotinylation of the purified antigen and subsequent use in immunohistochemistry with sections from tissue under analysis permits detection of the autoreactive B-cells and plasma cells. Double staining with cell-specific markers or for the presence of intracellular Ig allows characterization of the cell or determination of Ig isotype of the autoantibody produced by the individual autoreactive B -cell, leading to better understanding of the role of the particular antibody in the inflammatory cascade of the organ. With this technique, identification as well as quantification of autoreactive cells within tissues may be performed; it is also possible to analyze the spatial relation to residual cells or other infiltrating cells of the target organ.

One-step biotinylation procedure for carbohydrates to study carbohydrate–protein interactions

Protein-carbohydrate interactions play crucial roles in numerous biological processes. To study these interactions, we developed a simple and fast procedure for the biotinylation of carbohydrates based on reductive amination. The method allows complete and stable biotinylation of small quantities of oligosaccharides and includes a rapid and simple procedure to remove excess labeling reagent. After biotinylation, the structural and biological integrity of the glycans was intact as determined by HPLC, mass spectrometry, and a plant lectin assay. By using the human C-type lectin DC-SIGN (dendritic cell-specific ICAM-3-grabbing nonintegrin), we demonstrate that the biotinylated glycans can be used in a glycan array to determine binding specificities of lectins. Moreover, we show that fluorescent beads coated with selected biotinylated glycans bind to DC-SIGN-expressing dendritic cells in vitro. Finally, by using biotinylated high-mannose N-glycans, we could visualize DC-SIGN-expressing cells in lymph node tissue. The availability of easy biotinylation methods for oligosaccharides such as those described here greatly facilitates the functional analysis of lectins. In addition, the biotinylated glycans will be great tools for investigating functional lectin receptors in situ.

Cytoplasmic melanoma-associated antigen (CYT-MAA) serum level in patients with melanoma: a potential marker of response to immunotherapy?

Simple, noninvasive methods are needed to follow effectiveness of new treatments in patients with melanoma. In our study, we examined cytoplasmic melanoma-associated antigen (CYT-MAA) serum level in melanoma patients during immunotherapy. Sera of 117 patients were assayed for CYT-MAA by double-sandwich ELISA before and during treatment with a polyvalent, shed antigen, melanoma vaccine. Vaccine-treated patients included 30 with American Joint Committee on Cancer (AJCC) stage IIb or IIIa, 30 with stage IIc, IIIb or IIIc, 30 with resected stage IV and 27 with measurable stage IV disease. Prior to vaccine therapy, 63% of patients had elevated serum CYT-MAA with high levels of antigen in all disease stages. After initiation of therapy, the level declined in more than 90% of the positive patients and fell below the positive cut-off in 56% of these patients within 5 months. By contrast, there was no decline in CYT-MAA serum level in 11 patients who served as untreated controls with melanoma. Multivariate analysis of the treated patients using accelerated failure time Weibull models adjusted for stage and age showed that patients whose CYT-MAA serum level remained elevated during treatment were approximately 3 times more likely to recur or progress than patients who were consistently below the positive cut-off (hazard ratio = 3.42, 95% CI [1.38, 8.47], p = 0.0079). Measurement of CYT-MAA serum level appears to show potential as an early marker of prognosis in patients with stages IIb to IV melanoma. Measurement of CYT-MAA serum level during therapy could provide an intermediate marker of response in these patients.

Freshly prepared immune complexes with intermittent microwave irradiation result in rapid and high-quality immunostaining

We have previously reported that intermittent microwave irradiation shortened the primary or secondary antibody incubation time to 10 min in a special moist chamber. To achieve precise immunostaining within 1h, we attempted to generate a novel procedure, "freshly prepared immune complex with intermittent microwave irradiation (f-IC-M)". The advantage of this immunostaining procedure lies in a one-step incubation instead of primary and then secondary antibody application. In this study, we employed five primary antibodies to examine the efficiency and quality of this procedure. As expected, every primary antibody examined brought about precise immunostaining within 45 min for formalin-fixed, paraffin-embedded sections, and within 15 min for frozen sections. In addition, this procedure is able to generate double-immunoenzymatic staining with different enzyme-labeled primary antibodies if desired. As any combination of primary and secondary antibodies is possible by this one-step application, f-IC-M increases the efficiency of immunostaining without losing quality. Therefore, this procedure is able to rapidly provide diagnostic information to the pathologists.

Presence and prognostic significance of melanoma-associated antigens CYT-MAA and HMW-MAA in serum of patients with melanoma

With the goal of finding serological markers to monitor patients with early- as well as late-stage melanoma, we compared the levels of the cytoplasmic melanoma-associated antigens (CYT-MAA) and high-molecular-weight melanoma-associated antigen (HMW-MAA) in the sera of melanoma patients and controls. Using double-sandwich ELISA, we measured levels of both antigens in 117 patients and in 62 age- and sex-matched controls. Patients were stratified into four risk group based on stage of the disease. Serum levels of both markers were significantly higher in melanoma patients than in controls. CYT-MAA was the more sensitive marker, with 61% of patients showing elevated levels regardless of the stage of disease. HMW-MAA was elevated in 29%. Elevated CYT-MAA was also significantly correlated with poorer clinical outcome. By multivariate analysis (adjusting for stage and age), patients who had elevated CYT-MAA were 81% more likely to recur than patients with undetectable levels (hazard ratio=1.81, 95% CI=[1.07, 3.06], p-value=0.03). Elevated levels of HMW-MAA did not correlate with poor prognosis. These results suggest that both CYT-MAA and HMW-MAA are serum markers for residual melanoma in patients with resected disease. Furthermore, CYT-MAA appears to be a prognostic marker of clinical outcome in melanoma vaccine-treated patients.

Differential expression of chemokine receptors on human IgA+ and IgG+ B cells

Organ-specific lymphocyte homing is dependent on the expression of tissue-specific homing receptors and selected chemokine receptors. During the effector phase of an immune response, IgA and IgG antibody-secreting cells (ASC) are differently distributed in the body. Still, B cell expression of L-selectin and the mucosal homing receptor integrin alpha4beta7 is not related to the isotype produced, but only to the site of antigen encounter. In this study, we examined if differences in chemokine responsiveness between IgA+ and IgG+ B cells could explain their different tissue localization. Circulating CD19+ B cells were isolated and their expression of IgA, IgG, and selected chemokine receptors was determined by flow cytometry. Few Ig+ cells expressed CCR2, CCR3, or CCR9, and there was no difference in the expression of these receptors between IgA+ and IgG+ cells. In contrast, CCR4, CCR5, and CXCR3 was expressed on significantly more IgG+ than IgA+ cells. The function of chemokine receptors on memory B cells and ASC was then tested in the transwell system. IgG+ memory cells migrated to a higher extent than IgA+ cells towards the CXCR3 ligand CXCL11/I-TAC, while there was only a small migration towards the CCR4 ligand CCL17/TARC and the CCR9 ligand CCL25/TECK. ASC migrated poorly to all chemokines tested. In conclusion, this study shows that IgG+ and IgA+ memory B cells have a differential expression of the Th1 associated chemokine receptor CXCR3, as well as of CCR4 and CCR5. In contrast, none of the studied chemokine receptors was preferentially expressed by IgA+ cells.

A new immunofluorostaining method using red fluorescence of PerCP on formalin-fixed paraffin-embedded tissues

Immunofluorostaining, a versatile tissue staining method, is used in biomedical research because of its clear contrast and precise quantification of positive signals. However, its application in clinical diagnosis has been limited. A major obstacle is high fluorescent background of formalin-fixed, paraffin-embedded tissue sections (paraffin sections). On paraffin sections, strong and broad fluorescence of the section overlapping that of conventional fluorescent dyes such as fluorescein isothiocyanate (FITC) prevents detection of target immunofluorescence. To circumvent the background, we selected an albuminous dye, peridinin chlorophyll a protein (PerCP), for immunostaining of human tumor sections with tumor-reactive monoclonal antibodies. Red fluorescence of PerCP clearly distinguished the tumor region within the yellow-green autofluorescence of the section. Furthermore, it was possible to observe tissue morphology simultaneously without any counterstaining; autofluorescence served as counterstaining in this method. Digital quantification of PerCP-stained image intensity correlated (r2>0.99) well with extracted PerCP amount, indicating the usefulness of image quantification. We conclude that this new and simple immunofluorostaining method can be applied to pathological diagnosis of a wide range of conditions, including cancer.

Improved 1-h rapid immunostaining method using intermittent microwave irradiation: practicability based on 5 years application in Toyama Medical and Pharmaceutical University Hospital

Immunostaining depending on antigen-antibody specificity is the commonest approach for determining the localization of specific antigens in tissue sections. This procedure is applicable not only with frozen or specially fixed samples, but also has proved reliable with formalin-fixed paraffin-embedded tissue sections through improvement of antigen-retrieval. Immunostaining is thus firmly established as a tool for diagnostic pathology and in our institute multiple antibodies are applied for 13-15% of the cases examined, as well as H and E staining. With the standard approach, approximately 3 h is necessary from the beginning of deparaffinization till covering sections with the Envision system. We utilized intermittent microwave irradiation for 10 min during hybridization with primary and secondary antibodies in a special moist-chamber, to achieve all immunostaining steps within 1 h in 178 primary antibodies frequently used for diagnostic pathology. According to our 5 years experience, such microwave irradiation not only obtained significant specific staining for enhancing the specificity of antigen-antibody reactions, but also inhibited nonspecific binding. We present herein the details of the methodology and recommendations for its application with particular primary antibodies. This method can contribute to savings in time and energy, allowing pathologists to rapidly obtain diagnostic information.

How biotinylation can interfere with recognition: a surface plasmon resonance study of peptide-antibody interactions

Biotinylation is one of the most frequently used labelling procedures in biochemistry and molecular biology. To study the influence of biotinylation on peptide antigenicity, we selected a peptide derived from the second extracellular loop of the beta(2)-adrenergic receptor. Interactions between different biotinylated and nonbiotinylated analogs and a monoclonal antibody directed against an epitope present within the N-terminal end of this peptide were studied in detail. Taking advantage of the BIACORE 3000 surface plasmon resonance equipment, we were able to compare antibody interactions with the immobilised peptides and with the same peptides in solution. While the nonbiotinylated peptide, immobilised by its N-terminus, was not recognised by the antibody, it was recognised either after immobilisation by means of the thiol group of the C-terminal cysteine residue or as a free peptide tested as analyte with the monoclonal antibody immobilised on the chip. The N-terminal biotinylated forms were well recognised when immobilised on streptavidin but poorly (for the aminocaproyl-biotin derivative) or not at all (for the biotinylated derivative) when they were allowed to react with immobilised monoclonal antibody. These results indicate that the biotinyl moiety interacts with residues that are important for antibody recognition in solution but such interactions are abrogated when it is bound to the streptavidin. Molecular modeling confirmed that the N-terminus of the peptide mimicked to some extent the streptavidin binding site.

Development and effects of immunoliposomes carrying an antisense oligonucleotide against DHFR RNA and directed toward human breast cancer cells overexpressing HER2

The development and the effect of immunoliposomes directed against human breast cancer cells overexpressing p185/HER2 are described. These immunoliposomes carry an antisense oligonucleotide directed toward the translational start site of dihydrofalate reductase (DHFR) RNA, which causes high cytotoxicity. To prepare the immunoliposomes, we followed two methodologies based on the high affinity between streptavidin and biotin and the use of biotinylated antibodies. In the first approach, the streptavidin molecule is covalently attached to the phospholipid DOPE, which is mixed with the cationic liposome DOTAP complexed with the antisense oligonucleotide. The second approach, which is much easier to perform, involves the binding of streptavidin to antibody and oligonucleotide, both biotinylated, and the latter complexed with DOTAP. The formation of the intermediary complexes of this immunoliposome was studied sequentially by gel electrophoresis. The uptake of the oligonucleotide carried by the immunoliposome was monitored by flow cytometry and confocal microscopy. As a model, we used SKBR3 cells that overexpress p185. The full immunoliposomes were more toxic than the antisense oligonucleotide in the absence of the antibody, thus increasing the sensitivity of the treatment.

Endogenous biotin staining in a subset of spinal neuronal cell bodies: a potential confounding factor for neuroanatomical studies

Biotinylated compounds are commonly used to label neuronal cell bodies via intracellular filling or retrograde tracing. Endogenous concentrations of biotin within a subset of neuronal cell bodies would pose a problem for interpreting such experiments. Here I report that a subset of turtle spinal cord neuronal cell bodies strongly stains for biotin, using the avidin-biotin-horseradish peroxidase (ABC) reaction, in the absence of any exogenous biotinylated compound.

Single-molecule imaging of interaction between dextran and glucosyltransferase from Streptococcus sobrinus

Using total internal reflection fluorescence microscopy, we directly observed the interaction between dextran and glucosyltransferase I (GTF) of Streptococcus sobrinus. Tetramethylrhodamine (TMR)-labeled GTF molecules were individually imaged as they were associating with and then dissociating from the dextran fixed on the glass surface in the evanescent field. Similarly dynamic behavior of TMR-labeled dextran molecules was also observed on the GTF-fixed surface. The duration of the stay on the surface (dwell time) was measured for each of these molecules by counting the number of video frames that had recorded the image. A histogram of dwell time for a population of several hundred molecules indicated that the GTF-dextran interaction obeyed an apparent first-order kinetics. The rate constraints estimated for TMR-labeled GTF at pH 6.8 and 25 degrees C in the absence and presence of sucrose were 9.2 and 13.3 s(-1), respectively, indicating that sucrose accelerated the dissociation of GTF from dextran. However, the accelerated rate was still much lower than the catalytic center activity of GTF (> or = 25 s(-1)) under comparable conditions.

Comparative electrochemical behaviour of biotin hydrazide and photobiotin. Importance in the development of biosensors

The cyclic voltammetric behaviour of biotin hydrazide and photobiotin on carbon paste electrodes has been studied. Biotin hydrazide presents an anodic and irreversible process, meanwhile photobiotin presents two, adsorptive in nature. This characteristic makes photobiotin desirable for following the interaction between biotin and streptavidin, being possible to detect a streptavidin concentration of 10(-12) M. The evidence of this reaction has been shown either directly in solution or on the electrode surface. Photobiotin as the molecule portable of analytical information and carbon paste as the solid support could be applied to the development of sensors based on the oxidation of this molecule.

Infectivity and arthritis induction of Borrelia japonica on SCID mice and immune competent mice: possible role of galactosylceramide binding activity on initiation of infection

We investigated the relationship between the binding activity to galactosylceramide (GalCer) and the arthritis induction activity of Borrelia japonica. The B. japonica strains maintained the ability to induce arthritis in inbred C3H/HeN and immunodeficient SCID mice, but the ability was lower than that of Borrelia burgdorferi sensu stricto virulent strain 297. Histopathological changes were restricted to the joints, and a marked effusion of polymorphonuclear neutrophils into the joint space was found. The binding activity of B. japonica strains to GalCer was lower than that of the virulent strain 297 but higher than that of the high-passage strain 297. The lower infectivity and virulence of B. japonica may explain its lower binding ability to GalCer.

Biotin and digoxigenin as labels for light and electron microscopy in situ hybridization probes: where do we stand?

Biotin was recently applied to detect cellular DNA or RNA. In combination with avidin, streptavidin or antibody, it can be conjugated with fluorescent dye, enzyme, ferritin, or gold. However, emphasis has recently been placed on the false-positive results that are obtained when this probe is used, because endogenous biotin may sometimes interfere with specific signals. Digoxigenin appears to be an interesting alternative because it is present exclusively in Digitalis plants as a secondary metabolite. We discuss in this review the efficiency and the respective advantages and disavantages of these two probes for in situ hybridization, mainly at the electron microscopic level.

Endothelial Gi protein expression is markedly low in human coronary microvessels

Gi protein functionally mediates endothelium-dependent relaxations in large epicardial coronary arteries but not in small coronary arteries, which suggests a different involvement of Gi protein in the endothelium-dependent relaxations between large and small coronary arteries. We previously showed that endothelial Gi protein is present in human epicardial coronary artery. In the present study, we examined the expression of endothelial Gi protein in human coronary microvessels. Immunohistochemical staining with a specific antibody against human Gi protein was performed in intramyocardial coronary microvessels and vasa vasorum from 34 autopsy cases. The immunoreactive levels of the endothelial Gi protein were semiquantitated into four grades (none, 0; slight, +1; moderate, +2; high, +3), and the mean value of the ratings of all endothelial cells was then used as an index of the endothelial Gi protein expression of the vessel. The immunoreactive levels of the endothelial Gi protein were extremely low in intramyocardial coronary microvessels and in vasa vasorum, irrespective of the age of the patients, the presence or absence of coronary risk factors, or the influence of medical treatments. These results may therefore explain in part why endothelium-dependent relaxations in coronary microvessels are not functionally mediated by Gi protein.

Unprotected peptides as building blocks for branched peptides and peptide dendrimers

We describe two new site-specific ligation methods for preparing branched peptide dendrimers such as multiple antigen peptide (MAP). Both methods are based on the general approach of exploiting the specific reaction between a weak base and an aldehyde under acidic conditions so that unprotected peptides can be used as building blocks. A weak base such as benzoyl hydrazine or 1,2-amino thiol of cysteine was attached to the N-terminal of an unprotected peptide as nucleophile to react with the alkyl aldehyde on the core matrix of MAP to form a stable hydrazone linkage or a five-membered thiazolidine ring, respectively. Two synthetic peptides rich in basic amino acids such as lysine and arginine were used as models in the ligation reactions in solution to give peptide dendrimers containing four or eight copies of peptide immunogens. The resulting macromolecules with the MW ranging from 5 to 16 kDa were unambiguously characterized by laser-desorption mass spectrometry. Furthermore, we also optimized the conditions of these ligation reactions using elevated temperature and a water-miscible organic co-solvent to give a combination of rate enhancement about 10 fold. These optimizations allowed the ligation reactions to be completed in < 4 h instead of 2-3 days. Our ligation approach also has the advantages of flexibility so that peptides can be attached through the amino or carboxyl terminus to the core matrix. The phenyl hydrazone linkage and the five-membered ring were found to be stable at physiological pH suitable for immunization. Thus our results provide two practical and useful methods for the synthesis of macromolecular peptide dendrimers for vaccines, artificial proteins, and enzymes.

Preclinical pharmacology of cholera toxin

Cholera toxin was selected for pharmacologic evaluation by the National Cancer Institute on the basis of antiproliferative activity against small-cell and non-small-cell lung-cancer cell lines. A feature common to the sensitive cell lines was abundant expression of GM1 ganglioside, the cellular receptor for cholera toxin. A sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantitate cholera toxin in biological fluids. A sigmoidal relationship was observed between the cholera toxin plasma concentration and the absorbance at 490 nm (OD490) of the product of horseradish peroxidase-catalyzed oxidation of o-phenylenediamine over the range of 6.25-1,600 ng/ml. Logit transformation of the OD490 data was linear over the entire concentration range and assay variability was less than 25%. Cholera toxin was stable in murine and human whole blood and plasma. Following i.v. administration of 1,500 micrograms/kg to male CD2F1 mice, cholera toxin plasma elimination was described by a two-compartment open model. The half-lives (t1/2 alpha, t1/2 beta), plasma clearance, and steady-state volume of distribution were 0.7 min, 49 min, 24 ml min-1 kg-1 912 ml/kg, respectively. Cholera toxin was not detected in plasma following an s.c. dose of 1,500 micrograms/kg. Urinary recovery following intravenous drug administration was less than 0.1%.

Biotin staining in the giant fiber systems of the lobster

The avidin-biotin-complex method is a popular immunocytochemical technique. This method labels consistently a group of neurons in the lobster ventral nerve cord in the absence of primary antibodies. The specific staining is due to a relatively high level of endogenous biotin (or biocytin) in these neurons. These biotin-positive neurons are located in the supraesophageal, thoracic, and abdominal ganglia. Intraaxonal injection of Lucifer yellow followed by Texas red-conjugated streptavidin staining reveals that the neurons are members of the medial giant (MG) and lateral giant (LG) systems, which are important in mediating rapid tail flipping during escape maneuvers. In neuronal somata, staining is restricted to the cytoplasm. Within MG axons, staining appears as punctate, subaxolemmal structures. Preincubating nerve cords in biocytin or direct intraaxonal injection of biocytin enhances staining of these punctate organelles. In LG axons, staining is localized to fragments of braided filamentous structures that also appear to be associated with the axolemma. Preincubation of ventral nerve cords in various concentrations of biocytin results in the appearance of additional groups of stained neurons, suggesting that there are subsets of neurons with specific biocytin-uptake or -retention mechanisms. In the crayfish, biotin-positive staining is confined to the MG neurons; the LG neurons are not stained. In the earthworm, no staining is observed in the MG and LG axon escape systems. In the goldfish, no biotin-staining is seen in the Mauthner neurons and their axons. The significance of specific localization of biotin or biocytin to subsets of neurons is unclear. It may reflect the presence of high levels of biocytin moieties on biotin-dependent enzymes. Biotin is an important cofactor in the catalytic functions of several decarboxylases crucial in energy production and lipogenesis. Axons of the giant fiber systems in lobsters and crayfish may have high energy and fatty acid synthesis requirements. Increased levels of biotin accumulation may also be related to other functions of the giant axon systems, such as the formation of electrical synapses among themselves and with phasic motoneurons.

Staining of endothelial cells and macrophages in atherosclerotic lesions with human heat-shock protein-reactive antisera

Our previous epidemiological studies have shown that levels of serum antibodies against mycobacterial heat-shock protein (hsp) 65 correlate positively with carotid atherosclerosis in subjects aged 40 to 79 years. To determine whether these high-titer sera also react with homologous human hsp60 and/or cell components of atherosclerotic lesions, we selected 15 human sera samples, each with high or low titers to recombinant mycobacterial hsp65, and investigated their reactivity with human arterial lesion components by immunoblotting and immunofluorescence techniques. All five higher-titer sera against hsp65 reacted with a 60-kDa band of atherosclerotic lesion proteins and human recombinant hsp60 on Western blots. Pooled sera with low antibody titers to hsp65 diluted similarly as high-titer sera did not show reactivity with atherosclerotic lesion and media proteins. By immunohistochemistry and immunofluorescence with human immunoglobulin G isolated from different sera, labeled with biotin, and visualized with a streptavidin conjugate, positive staining was observed in sections of fatty streaks and atherosclerotic plaques of carotid arteries, and weak staining was observed in the normal intima. Double immunofluorescence identified the majority of positively stained cells as macrophages, endothelial cells, and a few smooth muscle cells. In summary, serum antibodies against hsp65 cross-react with the human 60-kDa homologue present in high levels in atherosclerotic lesions and are mainly reacting with macrophages and endothelial cells, supporting our concept of a possible involvement of humoral-mediated immune reaction against hsp60 in atherogenesis.

Suppression of B cell differentiation by ligation of membrane-bound IgM

Using B cells from the transgenic mouse line B6-Sp6 and control littermates, stimulated by lipopolysaccharide (LPS) under novel culture conditions that provide for the response of all B cells, we show here that specific ligation of the surface IgM molecules always results in inhibition of terminal differentiation and immunoglobulin secretion by activated cells, regardless of the ligand. Thus, monoclonal antibodies to (a) the CH region of Ig (anti-mu and anti-allotype), (b) the C kappa region, (c) the V region (anti-idiotype) of surface IgM, as well as (d) multivalent antigen (2,4,6-trinitrophenyl-bovine serum albumin), all show similar effects and dose-response curves. IgD-negative transgenic B cells are equally sensitive to IgM ligation-dependent inhibition, as control (IgD-positive) B cells. The allotype specificity of this inhibition, assessed by using anti-mu allotype reagents to inhibit and assay the responses, suggests that B cells expressing transgenic or endogenous IgM in transgenic B6-Sp6 mice are largely independent populations. These observations establish that anti-IgM antibodies in conjunction with appropriate LPS stimulation, provide a universal model system for functional characterization of B cell responses.

Increased expression of heat shock protein 65 coincides with a population of infiltrating T lymphocytes in atherosclerotic lesions of rabbits specifically responding to heat shock protein 65

We have shown previously that atherosclerotic lesions can be induced in normocholesterolemic rabbits by immunization with mycobacterial heat shock protein 65 (hsp65), which has a high degree of sequence homology with mammalian hsp60. To investigate a possible relationship between hsp60 expression and the antigenic specificities of infiltrating T cells in the lesion, 38 New Zealand White rabbits were treated either by immunization with recombinant mycobacterial hsp65 or by administration of a 0.2% cholesterol diet. Atherosclerotic lesions were observed after 16 wk, particularly in the aortic arch and arterial bifurcations of rabbits immunized with hsp65 or fed with a cholesterol-rich diet. Hsp65 staining of aortas showed a heterogeneous distribution, and significantly increased staining intensity in atherosclerotic lesions compared to aortic media or adventitia. This abundantly expressed hsp65 was observed in atherosclerotic lesions induced by hsp65 immunization as well as those induced by cholesterol-rich diet alone. Interestingly, a population of the T lymphocytes isolated from all forms of atherosclerotic lesions specifically responded to hsp65 in vitro. IL-2-expanded T cell lines derived from atherosclerotic lesions showed a significantly higher hsp65 reactivity than those developed from peripheral blood of the same donor. Furthermore, levels of circulating antibodies and numbers of spleen cells specifically reacting against hsp65 were elevated in all experimental animals. Flow cytometric analysis of spleen cells showed elevated immune response-associated antigen expression in treated animals. In conclusion, increased hsp65 expression in intimal cells and the presence of hsp65-specific T cells in blood and in atherosclerotic lesions may be important in initiating the development of atherosclerosis and perpetuating the lesions.

Induction of arteriosclerosis in normocholesterolemic rabbits by immunization with heat shock protein 65

Previous studies have established the presence of high numbers of activated T lymphocytes and "aberrant" expression of major histocompatibility complex class II antigens by endothelial and smooth muscle cells in human atherosclerotic lesions, implicating the involvement of a local cellular immune response. The identity of the antigen(s) eliciting this immune response, the extent of their effect, and the atherogenic stage at which they occur remain to be determined. In the present studies, 120 normocholesterolemic New Zealand White rabbits were immunized one or more times with various antigens, with or without adjuvants. The antigens and adjuvants included human or rabbit atherosclerotic lesion proteins, ovalbumin, Freund's complete and/or incomplete adjuvants, recombinant mycobacterial heat shock protein 65 (hsp65), and two hsp-free adjuvants, Ribi complete adjuvant and lipopeptide. In addition, some groups received a high-cholesterol diet. Sixteen weeks after the first immunization the animals were killed, and arteriosclerotic lesions in the intima of the aortic arch were found to have developed only in those animals immunized with antigenic preparations containing hsp, either in the form of whole mycobacteria or as purified recombinant hsp65, although their serum cholesterol levels were normal. No arteriosclerotic changes exceeding those of controls were found in the other groups, irrespective of the antigen used. Immunohistopathologic examination revealed that the lesions contained 20% T cells, 10-30% macrophages, and 10-40% smooth muscle cells. Analysis of the peripheral blood T-lymphocyte proliferative responses revealed that the occurrence of lesions was positively correlated with the presence of hsp65-reactive T cells, suggesting that hsp65 is involved in the induction of arteriosclerotic lesions. Furthermore, combined immunization with hsp-containing material and a cholesterol-rich diet provoked development of significantly more severe atherosclerosis and the appearance of characteristic foam cells. We conclude that an (auto)immune response to hsp may initiate the development of atherosclerosis and that a high blood cholesterol level is only one albeit a very important risk factor.

Multiple ICAM-1 (CD54) epitopes are involved in homotypic B-cell adhesion

Two monoclonal antibodies (MoAbs), F10.2 and F10.3, were selected for their ability to interfere in homotypic adhesion of human B cells. Precipitation studies and binding to intercellular adhesion molecule 1 (ICAM-1, CD54) cDNA transfected COS cells revealed that both MoAbs are directed against ICAM-1. The binding of MoAb F10.2 was inhibited by LB-2, a MoAb recognizing the NH2-terminal immunoglobulin-like domain of ICAM-1. This suggests that the epitope recognized by F10.2 is located on the first domain of the ICAM-1 molecule. Binding of the other MoAb, F10.3, was not inhibited by F10.2 nor by two other MoAbs mapping to the first domain of the ICAM-1 molecule. The ability of F10.3 to bind to ICAM-1 is influenced by glycosylation, suggesting that this epitope is located on one of the domains carrying possible glycosylation sites, i.e. domain 2, 3 or 4. The ICAM-1 epitopes recognized by F10.3 and LB-2 or F10.2 co-operated in homotypic adhesion of cells from the EBV cell line ML1. These results suggest that in addition to an epitope located on domain 1 of the ICAM-1 molecule, another epitope whose exposure can be regulated by glycosylation is involved in homotypic B-cell adhesion of cell line ML1.

Mechanisms of serum-enhanced adhesion of human alveolar macrophages to epithelial cells

Adhesive interactions between macrophages and epithelial cells in the pulmonary alveoli may be important in the pathogenesis of inflammatory lung diseases, such as those induced by cigarette smoking. Potential mechanisms controlling the interactions between these cells were investigated using human alveolar macrophages (AM) and MDCK or A549 epithelial cells. Five percent human serum enhanced the adhesion of AM to MDCK cells by approximately 6-fold and to A549 cells by approximately 1.7-fold. This enhancement was reduced by heating the serum for 30 min at 55 degrees C. Treating normal human serum with methylamine to inactivate C3, substituting C3-deficient serum, or pretreating serum-exposed MDCK cells with anti-C3 F(ab')2 all significantly diminished the adhesion of AM, suggesting that complement is involved. With the use of flow cytometry to examine complement receptors on AM, both CD11b/CD18 and CD11c/CD18 were detected but CR1 was not evident. Preincubating AM with a monoclonal antibody to CD18 reduced the adhesion of AM to MDCK cells by 40% while a significant reduction could not be demonstrated after preincubation with antibodies to either CD11b or CD11c. These data suggest that in the presence of serum C3bi is deposited on the surface of MDCK cells and that AM may attach to these cells, at least in part, through interactions between C3bi and one or more receptors in the CD11/CD18 family, which are present on AM.