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PubMed2005

Time-resolved fluorescence resonance energy transfer shows that the bacterial multidrug ABC half-transporter BmrA functions as a homodimer.

Members of the ATP-binding cassette (ABC) transporters share the same basic architecture, with a four-core domain made of two transmembrane plus two nucleotide-binding domains. However, a supramolecular organization has been detected in some ABC transporters, which might be relevant to physiological regulation of substrate transport. Here, the oligomerization status of a bacterial half-ABC multidrug transporter, BmrA, was investigated. Each BmrA monomer containing a single cysteine residue introduced close to either the Walker A or the ABC signature motifs was labeled using two probes, 2-(4-maleimidoanilino)naphthalene-6-sulfonic acid (fluorescence donor) or 4-dimethylaminophenylazophenyl-4'-maleimide (fluorescence acceptor). Reconstitution into proteoliposomes of BmrA monomers labeled separately with either the fluorescence donor or the fluorescence acceptor allowed measurement of time-resolved fluorescence resonance energy transfer between the two probes, showing that efficient reassociation of the singly labeled BmrA monomers occurred upon reconstitution. The efficiency of energy transfer studied as a function of increasing concentration of BmrA-labeled with the fluorescence acceptor argues for a dimeric association of BmrA instead of a tetrameric one. Furthermore, the efficiency of energy transfer allowed estimation of the distances between the two bound probes. Results suggest that, in the resting state, BmrA in a lipid bilayer environment preferentially adopts a closed conformation similar to that found in the BtuCD crystal structure and that the presence of different effectors does not substantially modify its global conformation.

ATP-Binding Cassette Transporters↗

PubMed2001

Overview: ABC transporters and human disease.

ABC transporters are found in all known organisms, and approximately 1,100 different transporters belonging to this family have been described in the literature. The family is defined by homology within the ATP-binding cassette (ABC) region, which extends outside of the more typical Walker motifs found in all ATP-binding proteins. Most family members also contain transmembrane domains involved in recognition of substrates, which are transported across, into, and out of cell membranes, but some members utilize ABCs as engines to regulate ion channels. There are approximately 50 known ABC transporters in the human, and there are currently 13 genetic diseases associated with defects in 14 of these transporters. The most common genetic disease conditions include cystic fibrosis, Stargardt disease, age-related macular degeneration, adrenoleukodystrophy, Tangier disease, Dubin-Johnson syndrome and progressive familial intrahepatic cholestasis. At least 8 members of this family are involved in the transport of a variety of amphipathic compounds, including anticancer drugs, and some appear to contribute to the resistance of cancer cells to chemotherapy.

ATP-Binding Cassette Transporters↗

PubMed2003

Heterotopic expression of class B floral homeotic genes supports a modified ABC model for tulip (Tulipa gesneriana).

In higher eudicotyledonous angiosperms the floral organs are typically arranged in four different whorls, containing sepals, petals, stamens and carpels. According to the ABC model, the identity of these organs is specified by floral homeotic genes of class A, A+B, B+C and C, respectively. In contrast to the sepal and petal whorls of eudicots, the perianths of many plants from the Liliaceae family have two outer whorls of almost identical petaloid organs, called tepals. To explain the Liliaceae flower morphology, van Tunen et al. (1993) proposed a modified ABC model, exemplified with tulip. According to this model, class B genes are not only expressed in whorls 2 and 3, but also in whorl 1. Thus the organs of both whorls 1 and 2 express class A plus class B genes and, therefore, get the same petaloid identity. To test this modified ABC model we have cloned and characterized putative class B genes from tulip. Two DEF- and one GLO-like gene were identified, named TGDEFA, TGDEFB and TGGLO. Northern hybridization analysis showed that all of these genes are expressed in whorls 1, 2 and 3 (outer and inner tepals and stamens), thus corroborating the modified ABC model. In addition, these experiments demonstrated that TGGLO is also weakly expressed in carpels, leaves, stems and bracts. Gel retardation assays revealed that TGGLO alone binds to DNA as a homodimer. In contrast, TGDEFA and TGDEFB cannot homodimerize, but make heterodimers with PI. Homodimerization of GLO-like protein has also been reported for lily, suggesting that this phenomenon is conserved within Liliaceae plants or even monocot species.

Amino Acid Sequence↗

PubMed1998

Crystal structure of the ATP-binding subunit of an ABC transporter.

ABC transporters (also known as traffic ATPases) form a large family of proteins responsible for the translocation of a variety of compounds across membranes of both prokaryotes and eukaryotes. The recently completed Escherichia coli genome sequence revealed that the largest family of paralogous E. coli proteins is composed of ABC transporters. Many eukaryotic proteins of medical significance belong to this family, such as the cystic fibrosis transmembrane conductance regulator (CFTR), the P-glycoprotein (or multidrug-resistance protein) and the heterodimeric transporter associated with antigen processing (Tap1-Tap2). Here we report the crystal structure at 1.5 A resolution of HisP, the ATP-binding subunit of the histidine permease, which is an ABC transporter from Salmonella typhimurium. We correlate the details of this structure with the biochemical, genetic and biophysical properties of the wild-type and several mutant HisP proteins. The structure provides a basis for understanding properties of ABC transporters and of defective CFTR proteins.

ATP-Binding Cassette Transporters↗

PubMed2003

Transcriptional regulation of ABC drug transporters.

P-glycoprotein, the founding member of the ATP-binding cassette (ABC) family of drug transporters, was first identified almost three decades ago and shown to confer resistance to multiple chemotherapeutic agents when overexpressed in human tumors. Subsequent years have witnessed a tremendous effort to characterize the function and regulation of P-glycoprotein, initially spurred by the hope that its inhibition was the key to overcoming clinical resistance to multiple anticancer agents. However, the identification of MRP1, another member of the ABC drug transporter family, led to the realization that the multidrug resistance (MDR) phenotype is considerably more complex than initially believed. Indeed, at the present time at least 10 members of the ABC transporter family have been implicated in an MDR phenotype, and it is likely that more will be added to this list as studies progress. With this complexity comes the imperative to improve our understanding of the function of individual transporters, as well as to delineate the mechanisms underlying their expression in normal and tumor cells, particularly those that may be amenable to therapeutic intervention. Several articles within this volume address the structure and function of drug transporters. This review will focus on our current understanding of the regulation of ABC drug transporters at the level of transcription.

ATP-Binding Cassette Transporters↗

PubMed2002

Overexpression and functional characterization of an ABC (ATP-binding cassette) transporter encoded by the genes drrA and drrB of Mycobacterium tuberculosis.

The genes encoding ATP-binding cassette (ABC) transporters occupy 2.5% of the genome of Mycobacterium tuberculosis. However, none of these putative ABC transporters has been characterized so far. We describe the development of expression systems for simultaneous expression of the ATP-binding protein DrrA and the membrane integral protein DrrB which together behave as a functional doxorubicin efflux pump. Doxorubicin uptake in Escherichia coli or Mycobacterium smegmatis expressing DrrAB was inhibited by reserpine, an inhibitor of ABC transporters. The localization of DrrA to the membrane depended on the simultaneous expression of DrrB. ATP binding was positively regulated by doxorubicin and daunorubicin. At the same time, DrrB appeared to be sensitive to proteolysis when expressed alone in the absence of DrrA. Simultaneous expression of the two polypeptides was essential to obtain a functional doxorubicin efflux pump. Expression of DrrAB in E. coli conferred 8-fold increased resistance to ethidium bromide, a cationic compound. 2',7'-bis-(2-Carboxyethyl)-5(6)-carboxyfluorescein (BCECF), a neutral compound, also behaved as a substrate of the reconstituted efflux pump. When expressed in M. smegmatis, DrrAB conferred resistance to a number of clinically relevant, structurally unrelated antibiotics. The resistant phenotype could be reversed by verapamil and reserpine, two potent inhibitors of ABC transporters.

ATP-Binding Cassette Transporters↗

PubMed1999

Two evolutionarily closely related ABC transporters mediate the uptake of choline for synthesis of the osmoprotectant glycine betaine in Bacillus subtilis.

Biosynthesis of the compatible solute glycine betaine in Bacillus subtilis confers a considerable degree of osmotic tolerance and proceeds via a two-step oxidation process of choline, with glycine betaine aldehyde as the intermediate. We have exploited the sensitivity of B. subtilis strains defective in glycine betaine production against glycine betaine aldehyde to select for mutants resistant to this toxic intermediate. These strains were also defective in choline uptake, and genetic analysis proved that two mutations affecting different genetic loci (opuB and opuC) were required for these phenotypes. Molecular analysis allowed us to demonstrate that the opuB and opuC operons each encode a binding protein-dependent ABC transport system that consists of four components. The presumed binding proteins of both ABC transporters were shown to be lipoproteins. Kinetic analysis of [14C]-choline uptake via OpuB (K(m) = 1 microM; Vmax = 21 nmol min-1 mg-1 protein) and OpuC (K(m) = 38 microM; Vmax = 75 nmol min-1 mg-1 protein) revealed that each of these ABC transporters exhibits high affinity and substantial transport capacity. Western blotting experiments with a polyclonal antiserum cross-reacting with the presumed substrate-binding proteins from both the OpuB and OpuC transporter suggested that the expression of the opuB and opuC operons is regulated in response to increasing osmolality of the growth medium. Primer extension analysis confirmed the osmotic control of opuB and allowed the identification of the promoter of this operon. The opuB and opuC operons are located close to each other on the B. subtilis chromosome, and their high sequence identity strongly suggests that these systems have evolved from a duplication event of a primordial gene cluster. Despite the close relatedness of OpuB and OpuC, these systems exhibit a striking difference in substrate specificity for osmoprotectants that would not have been predicted readily for such closely related ABC transporters.

ATP-Binding Cassette Transporters↗

PubMed2002

Functional analysis of a vacuolar ABC transporter in wild-type Candida albicans reveals its involvement in virulence.

ATP-driven transport proteins belonging to the ATP-binding cassette (ABC) superfamily perform important functions in cell metabolism and detoxification. Compounds can be actively transported across membranes, including the plasma membrane or organellar membranes. The vacuole is an important organelle in fungal cells required for compartmentalization of metabolites as well as toxic substances. Sequestration into the vacuole is often energy-dependent. We present the first isolation and molecular analysis of a vacuolar ABC transporter gene in the opportunistic fungal pathogen Candida albicans. The protein encoded by the MLT1 gene is highly similar to Multiple Drug Resistance-associated Protein (MRP)-like transporters of yeast and higher organisms that form the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)/MRP subfamily of ABC transporters, a class of proteins so far not characterized in C. albicans. MLT1 expression is extensively growth phase-regulated, and gene transcripts are inducible by metabolic poisons. Gene replacement mutants generated in wild-type C. albicans with the dominant selection marker MPAR showed a profound reduction in virulence in a mouse peritonitis model that was reversed by complementation with an intact MLT1 gene. Hence, this report provides primary evidence for the involvement of vacuolar ABC transporters in fungal virulence.

ATP-Binding Cassette Transporters↗

PubMed2003

Overexpression of a human and a fungal ABC transporter similarly suppresses the differentiation defects of a fungal peroxisomal mutant but introduces pleiotropic cellular effects.

Among the peroxisome membrane proteins, some are required for peroxisome biogenesis (e.g. PEX2) while others are not, e.g. ABC (ATP-binding cassette) transporters. Unexpectedly, overproduction of the peroxisomal ABC transporter PMP70 was found to be able to restore peroxisome biogenesis in mammalian pex2 mutant cell lines. In the filamentous fungus Podospora anserina, pex2 mutations not only impair peroxisome biogenesis but also cause a precise cell differentiation defect. Here, we show that both defects are partially suppressed by expression of the human cDNA encoding PMP70. In addition, PMP70 expression causes new developmental defects, different from those induced by pex2 mutations. We also show that overexpression of the P. anserina pABC1 gene, which encodes a peroxisomal ABC transporter, leads to similar effects. Taken together, our results demonstrate that: (i) the genetic relationship between PEX2 and PMP70, initially observed in mammals, has been conserved through evolution; (ii) the cell differentiation defect observed in the P. anserina pex2 mutants is indeed linked to impairment in peroxisome biogenesis; and (iii) unexpected detrimental cellular defects result from overproduction of peroxisomal ABC transporters.

ATP-Binding Cassette Transporters↗

PubMed2000

Symmetry and structure in P-glycoprotein and ABC transporters what goes around comes around.

The ABC superfamily of membrane transporters is one of the largest classes of proteins across all species and one of the most intensely researched. ABC proteins are involved in the trafficking of a diverse variety of biological molecules across cell membranes, with some members implicated in medical syndromes such as cystic fibrosis and multidrug resistance to anti-cancer drugs. In the absence of X-ray crystallographic data, structural information has come from spectroscopy, electron microscopy, secondary structure prediction algorithms and residue substitution, epitope labelling and cysteine cross-linking studies. These have generally supported a model for the topology of the transmembrane domains of ABC transporters in which a single aqueous pore is formed by a toroidal ring of 12 alpha helices, deployed in two arcs of six helices each. Although this so-called 6 + 6 helix model can be arranged in either mirror or rotational symmetry configurations, experimental data supports the former. In this review, we put forward arguments against both configurations of this 6 + 6 helix model, based on what is known generally about symmetry relationships in proteins. We relate these arguments to P-glycoprotein, in particular, and discuss alternative models for the structure of ABC transporters in the light of the most recent research.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2004

Ordered microstructures by assembly of ABC 3-miktoarm star terpolymers and linear homopolymers.

Ordered microstructures assembled from the mixture of the ABC 3-miktoarm star terpolymers and the linear homopolymers have been investigated by using dynamic density functional theory. The simulations reveal that completely different ordered microphase pattern is found with addition of a few percent homopolymers that is identical in component to one of the arms on the ABC 3-miktoarm star terpolymer. For example, the original density pattern of ABC 3-miktoarm star terpolymers with parameters of N(A)=N(B)=N(C)=10 and chi(AB)=0.90, chi(BC)=chi(CA)=0.45 is in a perfectly ordered knitting feature. However, with gradual addition of the linear polymer same as block C on ABC 3-miktoarm star terpolymer into the system, the density patterns evolve with the volume fraction of the linear polymer from the ordered knitting patterns into the hexagonal patterns. Furthermore, with addition of linear polymers same as block A, lamellar microstructure has finally resulted. The simulation points out a way for designing and manufacturing nanomaterials with totally different microstructures.

Journal Article↗

PubMed2002

Vanadate-catalyzed photocleavage of the signature motif of an ATP-binding cassette (ABC) transporter.

The maltose transport complex of Escherichia coli, a member of the ATP-binding cassette (ABC) superfamily, is made up of two nucleotide-binding subunits, MalK(2), which hydrolyze ATP with positive cooperativity, and two transmembrane subunits, MalF and MalG. The ABC family is defined in part by the canonical signature motif LSGGQ whose exact function remains controversial. Taking advantage of the dual function of vanadate as a transition state analogue and as a photoactive chemical, we demonstrate that vanadate catalyzes the UV-dependent cleavage of the polypeptide backbone at both the LSGGQ motif and the nucleotide-binding, or Walker A, motif when it is trapped in the nucleotide-binding site of the bacterial maltose transporter. This highly specific cleavage pattern indicates that residues in both motifs are immediately adjacent to ATP during hydrolysis, and are therefore likely to participate directly in ATP-binding and/or hydrolysis. Because the LSGGQ motif is too distant from the nucleotide in the structure of an ABC monomer for cleavage to occur, these data support a model in which the LSGGQ motif contacts the nucleotide across the interface of a MalK dimer, as seen in the crystal structure of Rad50. This architecture provides a basis for the cooperativity observed in the nucleotide-binding domains of ABC transporters and a function for this highly conserved family signature motif.

ATP-Binding Cassette Transporters↗

PubMed1998

ATPase and multidrug transport activities of the overexpressed yeast ABC protein Yor1p.

The Saccharomyces cerevisiae genome encodes 15 full-size ATP binding cassette transporters (ABC), of which PDR5, SNQ2, and YOR1 are known to be regulated by the transcription factors Pdr1p and Pdr3p (pleiotropic drug resistance). We have identified two new ABC transporter-encoding genes, PDR10 and PDR15, which were up-regulated by the PDR1-3 mutation. These genes, as well as four other ABC transporter-encoding genes, were deleted in order to study the properties of Yor1p. The PDR1-3 gain-of-function mutant was then used to overproduce Yor1p up to 10% of the total plasma membrane proteins. Overexpressed Yor1p was photolabeled by [gamma-32P]2', 3'-O-(2,4,6-trinitrophenyl)-8-azido-ATP (K0.5 = 45 microM) and inhibited by ATP (KD = 0.3 mM) in plasma membranes. Solubilization and partial purification on sucrose gradient allowed to detect significant Yor1p ATP hydrolysis activity (approximately 100 nmol of Pi.min-1.mg-1). This activity was phospholipid-dependent and sensitive to low concentrations of vanadate (I50 = 0.3 microM) and oligomycin (I50 = 8.5 microg/ml). In vivo, we observed a correlation between the amount of Yor1p in the plasma membrane and the level of resistance to oligomycin. We also demonstrated that Yor1p drives an energy-dependent, proton uncoupler-insensitive, cellular extrusion of rhodamine B. Furthermore, cells lacking both Yor1p and Pdr5p (but not Snq2p) showed increased accumulation of the fluorescent derivative of 1-myristoyl-2-[6-(NBD)aminocaproyl]phosphatidylethanolamine. Despite their different topologies, both Yor1p and Pdr5p mediated the ATP-dependent translocation of similar drugs and phospholipids across the yeast cell membrane. Both ABC transporters exhibit ATP hydrolysis in vitro, but Pdr5p ATPase activity is about 15 times higher than that of Yor1p, which may indicate mechanistic or regulatory differences between the two enzymes.

ATP-Binding Cassette Transporters↗

PubMed2001

The yeast a-factor transporter Ste6p, a member of the ABC superfamily, couples ATP hydrolysis to pheromone export.

ATP-binding cassette (ABC) proteins transport a diverse collection of substrates. It is presumed that these proteins couple ATP hydrolysis to substrate transport, yet ATPase activity has been demonstrated for only a few. To provide direct evidence for such activity in Ste6p, the yeast ABC protein required for the export of a-factor mating pheromone, we established conditions for purification of Ste6p in biochemical quantities from both yeast and Sf9 insect cells. The basal ATPase activity of purified and reconstituted Ste6p (V(max) = 18 nmol/mg/min; K(m) for MgATP = 0.2 mm) compares favorably with several other ABC proteins and was inhibited by orthovanadate in a profile diagnostic of ABC transporters (apparent K(I) = 12 microm). Modest stimulation (approximately 40%) was observed upon the addition of a-factor either synthetic or in native form. We also used an 8-azido-[alpha-(32)P]ATP binding and vanadate-trapping assay to examine the behavior of wild-type Ste6p and two different double mutants (G392V/G1087V and G509D/G1193D) shown previously to be mating-deficient in vivo. Both mutants displayed a diminished ability to hydrolyze ATP, with the latter uncoupled from pheromone transport. We conclude that Ste6p catalyzes ATP hydrolysis coupled to a-factor transport, which in turn promotes mating.

ATP-Binding Cassette Transporters↗

PubMedDate not supplied

Type 1 protein secretion in bacteria, the ABC-transporter dependent pathway (review).

The relatively simple type 1 secretion system in gram-negative bacteria is nevertheless capable of transporting polypeptides of up to 800 kDa across the cell envelope in a few seconds. The translocator is composed of an ABC-transporter, providing energy through ATP hydrolysis (and perhaps the initial channel across the inner membrane), linked to a multimeric Membrane Fusion Protein (MFP) spanning the initial part of the periplasm and forming a continuous channel to the surface with an outer membrane trimeric protein. Proteins targeted to the translocator carry an (uncleaved), poorly conserved secretion signal of approximately 50 residues. In E. coli the HlyA toxin interacts with both the MFP (HlyD) and the ABC protein HlyB, (a half transporter) triggering, via a conformational change in HlyD, recruitment of the third component, TolC, into the transenvelope complex. In vitro, HlyA, through its secretion signal, binds to the nucleotide binding domain (NBD or ABC-ATPase) of HlyB in a reaction reversible by ATP that may mimic initial movement of HlyA into the translocation channel. HlyA is then transported rapidly, apparently in an unfolded form, to the cell surface, where folding and release takes place. Whilst recent structural studies of TolC and MFP-like proteins are providing atomic detail of much of the transport path, structural analysis of the HlyB NBD and other ABC ATPases, have revealed details of the catalytic cycle within an NBD dimer and a glimpse of how the action of HlyB is coupled to the translocation of HlyA.

ATP-Binding Cassette Transporters↗

PubMedDate not supplied

Trypanosoma brucei glycosomal ABC transporters: identification and membrane targeting.

Trypanosomes contain unique peroxisome-like organelles designated glycosomes which sequester enzymes involved in a variety of metabolic processes including glycolysis. We identified three ABC transporters associated with the glycosomal membrane of Trypanosoma brucei. They were designated GAT1-3 for Glycosomal ABC Transporters. These polypeptides are so-called half-ABC transporters containing only one transmembrane domain and a single nucleotide-binding domain, like their homologues of mammalian and yeast peroxisomes. The glycosomal localization was shown by immunofluorescence microscopy of trypanosomes expressing fusion constructs of the transporters with Green Fluorescent Protein. By expression of fluorescent deletion constructs, the glycosome-targeting determinant of two transporters was mapped to different fragments of their respective primary structures. Interestingly, these fragments share a short sequence motif and contain adjacent to it one--but not the same--of the predicted six transmembrane segments of the transmembrane domain. We also identified the T. brucei homologue of peroxin PEX19, which is considered to act as a chaperonin and/or receptor for cytosolically synthesized proteins destined for insertion into the peroxisomal membrane. By using a bacterial two-hybrid system, it was shown that glycosomal ABC transporter fragments containing an organelle-targeting determinant can interact with both the trypanosomatid and human PEX19, despite their low overall sequence identity. Mutated forms of human PEX19 that lost interaction with human peroxisomal membrane proteins also did not bind anymore to the T. brucei glycosomal transporter. Moreover, fragments of the glycosomal transporter were targeted to the peroxisomal membrane when expressed in mammalian cells. Together these results indicate evolutionary conservation of the glycosomal/peroxisomal membrane protein import mechanism.

ATP-Binding Cassette Transporters↗

PubMed2004

Quantification of CD38 expression in B-cell chronic lymphocytic leukemia (B-CLL): a comparison between antibody binding capacity (ABC) and relative median fluorescence (RMF).

We have previously shown that quantification of CD38 expression using microbeads of specific antibody binding capacity (ABC) improves the prognostic value of CD38 expression in B-cell chronic lymphocytic leukemia, particularly for Binet Stage A patients. Quantification of CD38 expression using beads is expensive, time consuming and could be difficult to implement in a routine clinical laboratory. The calculation of relative median fluorescence (RMF) using the median fluorescence intensities of the test and control samples, is even more simply and cheaply obtained by flow cytometry and could be used as an alternative way of quantifying antigen expression. The present study demonstrates that RMF is an effective prognostic indicator in B-CLL that correlates closely with ABC in predicting disease-specific survival and time to progression for all patients. RMF predicted overall survival and time to progression in all patients (P < 0.0001 for both), in Binet Stage A patients (P < 0.0001 for both) and in Stage A patients under 60 years (P = 0.0299 and P = 0.0143, respectively). ABC predicted overall survival and time to progression in all patients (P < 0.0001 for both) in Stage A patients (P = 0.0024 and P < 0.0001, respectively) and in Stage A patients under 60 (P = 0.0379 and P = 0.0032, respectively). RMF is more effective than percentage CD38 positivity > 30% or > 20% in predicting disease-specific survival in Stage A patients of all ages (CD38 < > 30%: P = 0.0853, CD38 < > 20%: P = 0.0894) and in those under 60 years old (CD38 < > 30%: P = 0.5438, CD38 < > 20%: P = 0.2872). Also, RMF is more effective in predicting time to progression of Binet Stage A patients less than 60 years (P = 0.0143), while percentage CD38 positivity of 30%, 20% or 7% did not achieve statistical significance (P = 0.1103, = 0.0547, = 0.3399, respectively). We suggest that CD38 RMF could be used clinically as an alternative to ABC to identify patients with B-CLL that are likely to progress and require early treatment.

ADP-ribosyl Cyclase↗

PubMed1984

A comparison of indirect immunofluorescence and the avidin-biotin-peroxidase conjugate technic (ABC) in the performance of the antinuclear antibody test.

Antinuclear antibody tests were performed on 19 patients using both the indirect immunofluorescence procedure (FANA) and the avidin-biotin conjugated immunoperoxidase technic (ABC) on HEp-2 cells. Pearson r between the two tests was 0.73. Identical patterns were seen in only 53% of cases, due partially to the chromogen used and partially to positive staining with the ABC method in the face of negative results using the FANA. Reasons are presented to suggest that the ABC method is capable of detecting low-level autoantibodies. Because of the discrepancies seen, the ABC method is currently not recommended as a substitute for the FANA in a clinical setting.

Antibodies, Antinuclear↗