Molecular identification of the lobster muscle protein tropomyosin as a seafood allergen

Crustaceans are a major cause of seafood allergy. Recent studies have identified tropomyosin as the major allergen in shrimp. However, such data are lacking in other crustaceans. In the present study lobster allergens were identified and characterized by molecular cloning, sequencing, and expression. An IgE-reactive complementary DNA clone of 2 kilobase pairs (kb) was identified by screening an expression library of the spiny lobster Panulirus stimpsoni using sera from subjects with crustacean allergy. Expression and sequencing of this clone showed that it has an opening reading frame of 274 amino acids, coding for a 34-kDa protein designated as Pan s I. In addition, we expressed the fast muscle tropomyosin from the American lobster Homarus americanus and found that this protein, coined Hom a I, was also recognized by IgE from patients with crustacean allergies. The deduced amino acid sequences of Pan s I and Hom a I, which are the first identified lobster allergens, show significant homology to shrimp tropomyosin. Sera from subjects with crustacean allergies, when preabsorbed with recombinant proteins Pan s I or Hom a I, lost their IgE reactivity to muscle extract of P. stimpsoni and H. americanus. Preincubation of crustacean allergy sera with the recombinant shrimp tropomyosin Met e I also removed their IgE reactivity to lobster muscle extracts. The results suggest that patients with allergic reactions to crustaceans have common and possibly cross-reactive IgE-reactive epitopes in lobster and shrimp.

Differential gene expression of angiotensin II receptor subtypes in the epididymides of mature and immature rats

Previous studies have suggested that epididymal and sperm functions are subject to control by a local renin-angiotensin II system (RAS) in the rat epididymis. Type-1 angiotensin II receptor, AT1 and type-2 receptor, AT2 were localized in epididymal epithelium, indicating that RAS may act in a paracrine or autocrine fashion to regulate fluid secretion, probably through the basally placed membrane-bound AT1 protein as revealed by immunocytochemical and electrophysiological studies. In the present work, the expression of the angiotensin II receptor subtypes in the rat epididymis was showed by western blot analysis and reverse-transcription polymerase chain reaction (RT-PCR) using specific primers for the angiotensin II receptor subtypes. Western blot analysis showed the expression of AT1 receptor in the rat epididymis. Results from RT-PCR, using specific primers based on the corresponding angiotensin II receptor subtype genes for AT1a, AT1b and AT2 , demonstrated the differential expression of mRNAs from these receptor subtypes in the epididymides of mature and immature rats. Both the genes for AT1a and AT1b, but not that for AT2, are predominantly expressed in the epididymides of mature rat. In contrast, only AT1a and AT2 were highly expressed in the epididymides of immature rat. These results suggest that the expression of type-1 and type-2 angiotensin II receptor subtypes are developmentally regulated. Type-1 subtype may play a role in regulation of electrolyte and fluid transport in mature rat whereas type-2 subtype may be important in growth and development in the immature rat.

Immunohistochemical localization of angiotensin II in the mouse pancreas

Previous studies have suggested the presence of a tissue renin-angiotensin II system in the pancreas. These studies were based on the observation of several key components of the renin-angiotensin II system using molecular biological, biochemical and pharmacological approaches. In the present study, angiotensin II was localized immunohistochemically in the mouse pancreas using an indirect immunoperoxidase-staining technique. The results showed that angiotensin II-like immunoreactivity was localized predominantly in the endothelial cells of pancreatic blood vessels and the epithelial cells of pancreatic ducts from a subgroup of the vessels and ducts. Compared with those found in the pancreatic blood vessels and ductal system, a less pronounced immunoreactivity for angiotensin II was also observed in the acinar cells and in the smooth muscle layers overlying the pancreatic ducts as well as the blood vessels. However, no angiotensin II-like immunoreactivity was detected in the islet cells. Taken together with previous findings, the present results suggest a local angiotensin II-forming system in the mouse pancreas, which may be a significant autocrine or paracrine modulator of diverse pancreatic functions, including regulation of pancreatic blood flow and pancreatic anion secretion.

Clinicopathological study of primary biliary cirrhosis negative for antimitochondrial antibodies

Primary biliary cirrhosis (PBC) is characterized by the occurrence of antimitochondrial antibodies (AMA) and the progressive destruction of intrahepatic bile ducts, followed by biliary cirrhosis. However, there are about 5% of PBC patients who show clinicopathological features of PBC but are negative for AMA. In this study, clinicopathological features, as well as antibody reactivity against recombinant (r)-mitochondrial polypeptides, were examined in 30 AMA negative PBC patients and 38 AMA positive PBC patients, in whom the presence of AMA had been determined by indirect immunofluorescence (IF). There were few differences in the clinical and serological features between both groups. Histopathologic features, including staging, bile duct lesions and granuloma, were also similar in both groups. Among the 30 IF-tested AMA negative patients, 29 were also negative against beef heart mitochondrial proteins, but 24 reacted to one or more of the following r-polypeptides, as determined by immunoblotting: E1 alpha of pyruvate dehydrogenase complex, the E2 subunit of pyruvate dehydrogenase complex, and the branched-chain 2-oxo-acid dehydrogenase complex. The remaining six AMA-negative patients were asymptomatic, and histologically resembled having stage 1 of the disease, with relatively mild lymphocytic piecemeal necrosis. One case was positive for anti-smooth muscle antibody. The other clinicopathological features of these patients were similar to those of other AMA negative patients. The present study found that a majority of the AMA-negative patients fulfilling other clinicopathological criteria of PBC, had features similar to the AMA-positive PBC patients, and that a majority of IF AMA-negative patients were positive for r-polypeptides of the 2-oxo-acid dehydrogenase complex. It seems that nearly all the AMA negative patients possess a broad spectrum of antibody profile of AMA, in addition to clinicopathological and serological features.

Persistence of autoantibodies against recombinant mitochondrial and nuclear pore proteins after orthotopic liver transplantation for primary biliary cirrhosis

Primary biliary cirrhosis is an autoimmune disease characterized by high titer autoantibodies predominantly against mitochondrial antigens PDC-E2, BCOADC-E2 and OGDC-E2. Currently orthotopic liver transplant (OLT) is the major form of treatment for end-stage primary biliary cirrhosis (PBC), but it is still unclear whether the autoimmune response continues post-transplantation. In this study we took advantage of a well-defined collection of sera collected serially before and after liver transplantation. We assayed these sera for quantitative and isotype-specific titers of antibodies against a set of recombinant mitochondrial autoantigens. We also studied reactivity to gp210. Serum samples were taken before transplantation and at intervals of 6 months, 1, 2, and 3 years after OLT. Before OLT 24/35 patients were AMA-positive, including seven out of the 35 to PDC-E2 alone, eight to both PDC-E2 and OGDC-E2, six to both PDC-E2 and BCOADC-E2, two to BCOADC-E2 alone and one to OGDC-E2. Following OLT, the frequency of sera that responded to PDC-E2 alone increased from seven to 12/35. Similarly, reactivity to BCOADC-E2 slightly increased from two to four out of 35. However, there was an overall decrease in sera that responded to more than one antigen. Neither Ig isotype nor subclass of the autoimmune response changed following OLT. Findings with gp210 were similar, in that reactivity to gp210 was found in nine out of 35 patients pre-OLT; following OLT the frequency decreased to seven out of 35 patients. Overall, the titers of AMAs decline slightly during the first year post-OLT, but are equivalent to pre-OLT values by 6 months. Moreover, the antibody subclass/ isotype remained unchanged. These data suggest that the removal of a diseased PBC liver has little, if any, impact on the serological characteristics of PBC. Moreover, it provides information regarding the natural history of PBC, particularly on the long latency time for disease development.

Local regulation of epididymal anion secretion by pituitary adenylate cyclase-activating polypeptide

The present study investigated the role of pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of electrogenic anion secretion by the rat cauda epididymal epithelium. PACAP38, which has been shown to affect secretory function in various exocrine and endocrine tissues, gave rise to a concentration-dependent increase in the short-circuit current (Isc). The PACAP38 effect was restricted to the apical aspect of the epididymal cells. The Isc response to PACAP38 was abolished in Cl-(-)free solution and completely inhibited by the Cl- channel blocker, diphenylamine-dicarboxylic acid. The Isc response to PACAP38 was also suppressed by pretreatment of the cells with the adenylate cyclase inhibitor, MDL12330A. The localization of PACAP38 was further investigated using an immunohistochemical technique. PACAP38 immunoreactivity was observed in the cauda epididymal tubules as well as in the cultured epithelium, indicating its epithelial origin. The present results suggest that Cl- secretion in the epididymis may be regulated by PACAP38, which could be locally synthesized and released by the epithelial cells, in a paracrine or autocrine fashion.

Angiotensin II receptors, AT1 and AT2 in the rat epididymis. Immunocytochemical and electrophysiological studies

Previous work from our laboratory has provided evidence for the presence of a tissue renin-angiotensin system in the rat epididymis. In the current investigation, the regional localization of angiotensin II receptors, type I (AT1) and type II (AT2) was studied immunocytochemically using specific anti-peptide antibodies against the second extracellular loops of AT1 and AT2 receptors, and pharmacologically using specific receptor antagonists in conjunction with the short-circuit current technique. The immunocytochemical results showed that AT1 and AT2 immunoreactivities were predominantly localized in the basal region of the epididymal epithelium. Electrophysiological studies using the short-circuit current technique demonstrated a stimulatory effect of basolaterally applied angiotensin II on the epididymal electrogenic ion transport. This effect was inhibitable by the addition of AT1 antagonist, losartan but not by AT2 antagonist, PD123177, indicating a functional role of AT1 in epididymal electrolyte transport. The present finding suggests that angiotensin II receptors may play an important role in the regulation of epididymal function.

Localization of angiotensin II receptor subtypes AT1 and AT2 in the pancreas of rodents

Previous studies have demonstrated the existence of several key components of the renin-angiotensin system in the pancreas. In the present study, the localization of angiotensin II receptor subtypes, type I (AT1) and type II (AT2), in the mouse and the rat pancreas was studied by immunocytochemistry using specific antipeptide antibodies against the second extracellular loops of AT1 and AT2 receptors in conjunction with confocal laser scanning microscopy. In the mouse, immunoreactivity for AT1 and AT2 was observed predominantly in the endothelia of the blood vessels and the epithelia of the pancreatic ductal system. Similar distribution of immunoreactivity for AT1 and AT2 was also observed. However, the intensity of immunoreactivity for AT1 and AT2 was stronger in the rat than that found in the mouse pancreas. Much weaker immunostaining for both AT1 and AT2, as compared with that found in ductal regions, was also found in the acini of the rodent pancreas. Together with the previous findings, the present results suggest that AT1 and/or AT2 receptors may play a role in regulating pancreatic functions in the rodent.

Angiotensin II receptors: localization of type I and type II in rat epididymides of different developmental stages

Previous studies from our laboratory have provided evidence for the existence of a local renin-angiotensin system in the rat epididymis. Evidence has also accumulated, indicating that locally formed angiotensin II from the rat epididymis may play a paracrine and/or autocrine role in regulating epididymal electrolyte and fluid transport. In the present study, specific anti-peptide antibodies against the second extracellular loops of angiotensin II type I (AT1) and type II (AT2) receptors were used to localize immunocytochemically these receptors in the rat cauda epididymides of three developmental stages, namely, immature (2-week), early mature (6-week) and fully mature (10-week). The immunostaining intensity for AT1 receptors was found to be stronger than that for AT2 receptors throughout rat epididymides of all stages. However, the immunostaining for both AT1 and AT2 receptors observed in the fully mature rat epididymis was much more intense than that observed in the epididymides of the two younger stages. While the immunostaining for both AT1 and AT2 receptors in the younger rat epididymides appeared to be distributed in both basal and apical regions, the immunostaining in the fully mature epididymis was predominantly localized in the basal region. The present finding of the differential patterns of angiotensin II receptor immunoreactivity in three different stages of the rat epididymis may reflect the fine tuning of rat epididymal function by angiotensin II, acting as a paracrine or autocrine agent, during the course of development.

Comparative studies of antimitochondrial autoantibodies in sera and bile in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by destruction of intrahepatic bile ducts. Although the pathogenesis of this disease is still unknown, high titers of antimitochondrial autoantibodies (AMA) have long been recognized in patient sera. However, little is known about the presence of AMA in bile. In this study, we investigated bile and sera from patients with PBC and healthy controls for the presence of AMA and mitochondrial autoantigens. AMA were detected in the bile of 17 of 19 patients (89.4%) with PBC; they were specifically directed against the pyruvate dehydrogenase complex (PDC-E2) in 15 of 19 patients (78.9%), to the branched-chain 2-oxo-acid dehydrogenase complex E2 (BCOADC-E2) in 6 of 19 patients (31.6%), and to the 2-oxoglutarate dehydrogenase complex E2 (OGDC-E2) in 1 of 19 patients (5.3%). In a comparative study of sera from the same patients, anti-PDC-E2 antibodies were found in 19 of 19 patients (100%), anti-BCOADC in 9 of 19 patients (47.3%), and anti-OGDC-E2 in 4 of 19 patients (21.1%) patients. AMA in bile were always found together with antibodies of corresponding specificities in the serum from the same patient. Immunoglobulin (Ig)A AMA were found in the bile of 9 of 19 patients (47.7%) with PBC; they were specifically directed against PDC-E2 in 8 of 19 patients (42.1%) and to BCOADC in 2 of 19 patients (10.5%). Epitope mapping of IgA anti-PDC-E2 antibodies indicated that, like serum autoantibodies, the immunodominant epitope is directed against the inner lipoyl domain of PDC-E2. The prevalence and antigen reactivity of IgA AMA in sera correlated completely with IgA AMA in bile. Autoantibodies against nuclear envelope pore proteins (gp210) were found in 1 of 8 (12.5%) sera of patients with PBC, but not in bile. Furthermore, and of particular interest, we detected the autoantigens, PDC-E2, OGDC-E2, and BCOADC-E2, in the bile of 12 of 19 patients (63.2%), 9 of 19 patients (47.4%), and 9 of 19 patients (47.4%), respectively; PDC-E2 was found in only 1 of 17 (5.9%) disease controls. Although the presence of AMA in bile may merely reflect the presence of these antibodies in sera, the simultaneous detection of mitochondrial autoantigens in bile suggests an increase of mitochondrial autoantigens at inflammatory sites. Such autoantigens, coupled with AMA, may augment the local immune response and disease progression.

Electrogenic ion transport in the mouse endometrium: functional aspects of the cultured epithelium

A primary culture of mouse endometrial epithelium grown on permeable supports was established and the electrogenic ion transport across the endometrial epithelium was studied using the short-circuit current (I(SC)) technique. Enzymatically isolated mouse endometrial cells were immunostained with epithelial cells markers, cytokeratins, indicating an epithelial origin of the culture. Mouse endometrial epithelial cells grown on Millipore filters formed polarized monolayers with junctional complexes as revealed by light and electron microscopy. The cultured monolayers exhibited an average basal I(SC) of 4.6 +/- 0.3 microA/cm2, transepithelial voltage of 2.7 +/- 0.2 mV and transepithelial resistance of 599 +/- 30 omega cm2. The basal current was reduced by 85% in Na+-free solution and 13% in Cl(-)-free solution. The basal current could also be substantially (57.7%) blocked by an apical Na+ channel blocker, amiloride (10 microM), suggesting that Na+ absorption largely contributed to the basal current. Apical addition of Cl- channel blocker, DPC (2 mM), also exhibited an inhibitory effect, 19.4%, on the basal I(SC), indicating minor involvement of Cl- secretion as compared to that of Na+ absorption. The cultured endometrial epithelium also responded to a number of secretagogues including adrenaline and forskolin with increases in the I(SC), which could involve substantial Cl- secretion. The present study has established a culture of mouse endometrial epithelium exhibiting predominantly Na+ absorption under unstimulated condition, and Cl- secretion in response to various secretagogues. This culture may be useful for studying various regulatory mechanisms of electrogenic ion transport across the endometrial epithelium.

Angiotensin II receptor type I-regulated anion secretion in cystic fibrosis pancreatic duct cells

The beta-adrenergic (cAMP-dependent) regulation of Cl- conductance is defective in cystic fibrosis (CF). The present study explored alternative regulation of anion secretion in CF pancreatic ductal cells (CFPAC-1) by angiotensin II (AII) using the short-circuit current (ISC) technique. An increase in ISC could be induced in CFPAC-1 cells by basolateral or apical application of AII in a concentration-dependent manner (EC50 at 3 microm and 100 nm, respectively). Angiotensin receptor subtypes were identified using specific antagonists, losartan and PD123177, for AT1 and AT2 receptors, respectively. It was found that losartan (1 microm) could completely inhibit the AII-induced ISC, whereas, PD123177 exerted insignificant effect on the ISC, indicating predominant involvement of AT1 receptors. The presence of AT1 receptors in CFPAC-1 cells was also demonstrated by immunohistochemical studies using specific antibodies against AT1 receptors. Confocal microscopic study demonstrated a rise in intracellular Ca2+ upon stimulation by AII indicating a role of intracellular Ca2+ in mediating the AII response. Depletion of intracellular but not extracellular pool of Ca2+ diminished the AII-induced ISC. Treatment of the monolayers with a Cl- channel blocker, DIDS, markedly reduced the ISC, indicating that a large portion of the AII-activated ISC was Cl--dependent. AII-induced ISC was also observed in monolayers whose basolateral membranes had been permeabilized by nystatin, suggesting that the ISC was mediated by apical Cl- channels. Our study indicates an AT1-mediated Ca2+-dependent regulatory mechanism for anion secretion in CF pancreatic duct cells which may be important for the physiology and pathophysiology of the pancreas.

In situ nucleic acid hybridization of cytokines in primary biliary cirrhosis: predominance of the Th1 subset

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by destruction of the intrahepatic bile ducts. It is generally believed that cellular immune mechanisms, particularly involving T cells, result in this bile duct damage. The relative strength of Th1 and Th2 responses has recently been proposed to be an important factor in the pathophysiology of various autoimmune diseases. In this study, we have attempted to identify the Th subset balance in PBC, by detection of cytokines specific to the two T-cell subsets, i.e., interferon gamma (IFN-gamma) for Th1 cells and interleukin-4 (IL-4) for Th2 cells. We analyzed IFN-gamma and IL-4 messenger RNA (mRNA) positive cells in liver sections from 18 patients with PBC and 35 disease controls including chronic active hepatitis C, extrahepatic biliary obstruction (EBO), and normal liver, using nonisotopic in situ hybridization and immunohistochemistry. Mononuclear cells expressing IFN-gamma and IL-4 mRNA were aggregated in inflamed portal tracts in PBC livers, but were rarely present in extrahepatic biliary obstruction, alcoholic fibrosis, or normal liver sections. The IFN-gamma and IL-4 mRNA positive cells in PBC livers were detected in significantly higher numbers than in control livers (P < .01). Moreover, IFN-gamma mRNA expression was more commonly detected than IL-4 expression in PBC livers, and the levels of IFN-gamma mRNA expression were highly correlated with the degree of portal inflammatory activity. IFN-gamma mRNA-positive cells were detected primarily around damaged bile ducts that were surrounded by lymphoid aggregates. The data indicate that Th1 cells are the more prominent T-cell subset in the lymphoid infiltrates in PBC.

Antimitochondrial antibodies in primary biliary cirrhosis

In the last decade, the cloning and biochemical identification of mitochondrial autoantigens in primary biliary cirrhosis (PBC) as members of the 2-oxoacid dehydrogenase complex has greatly advanced the detection of antimitochondrial antibodies (AMA) and the understanding of the immunobiology of the disease. Here, we discuss the methods of detecting AMA and its isotypes, methods of epitope mapping, and using these methods in PBC liver immunohistochemistry and Ig gene usage. Increasing evidence, including the specific association of AMA with PBC, the unique similar but noncross-reactive conformational epitope of the lipoyl domains of the mitochondrial autoantigens, the specific binding of anti-PDC-E2 monoclonal antibodies and human combinatorial antibodies derived from PBC patients to the apical area of bile duct epithelial cells in PBC livers, and Ig gene usage of AMA, suggests that AMA is not an epiphenomenon of the disease but plays a significant role in the pathogenesis of PBC.

In situ nucleic acid hybridization of pyruvate dehydrogenase complex-E2 in primary biliary cirrhosis: pyruvate dehydrogenase complex-E2 messenger RNA is expressed in hepatocytes but not in biliary epithelium

Pyruvate dehydrogenase-E2, or a cross-reactive molecule, has been shown by a variety of immunohistochemical methods to be present in increased amounts in biliary epithelial cells (BEC) in primary biliary cirrhosis (PBC). In this study, to further understand the nature of the immunoreactive molecule in BEC, we examined the expression of pyruvate dehydrogenase complex-E2 (PDC-E2) messenger RNA (mRNA) and PDC-E2 protein in sections of livers from patients and controls to help identify the molecule found in BEC. We performed in situ hybridization using an antisense probe against the major epitope of PDC-E2. The data were very striking and suggested that there was no increased production of PDC-E2 in BEC. For example, in livers from patients with PBC, PDC-E2 mRNA was found in periportal hepatocytes in 16 of 17 cases (94%). In contrast, interlobular bile ducts and septal bile ducts had detectable levels of PDC-E2 mRNA in only 1 of 17 (6%) and 3 of 8 (38%) cases, respectively. Interestingly, proliferating bile ductules contained detectable levels of mRNA in 12 of 15 cases (80%). In control liver, periportal hepatocytes were positive in 15 of 17 cases (88%). Interlobular bile ducts, septal bile ducts, and proliferating bile ductules expressed mRNA signals in 4 of 17 (24%), 2 of 10 (20%), and 14 of 16 (88%), respectively. When formalin-fixed, paraffin-embedded sections were examined by immunohistochemical staining with anti-PDC-E2 monoclonal antibody (mAb) C355.1, the interlobular bile ducts showed typical aberrant apical staining in all 10 PBC cases, but 0 of 9 liver controls. Periportal hepatocytes, proliferating bile ductules and infiltrating mononuclear cells stained with C355.1 but in a characteristic mitochondrial staining pattern. The presence of a PDC-E2-like molecule recognized by C355.1 is not reflected by the expression levels of PDC-E2 mRNA in the BEC of patients with PBC.

Quantitative measurement of autoantibodies to recombinant mitochondrial antigens in patients with primary biliary cirrhosis: relationship of levels of autoantibodies to disease progression

We examined the clinical usefulness of measurements of antimitochondrial autoantibodies (AMA) in predicting disease progression in patients with primary biliary cirrhosis (PBC). We determined the relationships between AMA levels measured by indirect immunofluorescence (IF) and those measured by quantitative enzyme immunoassays (EIAs) using recombinant 2-oxo-acid dehydrogenase complex (2-OADC) proteins and the Mayo Risk Score, an established indicator of disease progression in primary biliary cirrhosis (PBC). Results of tests for AMA by either method correlated weakly (r = .24 to .30) with disease progression as indicated by Mayo Risk Scores. The levels of AMA to 2-OADC proteins varied by more than 200-fold between patients but remained relatively constant over time in individual patients. Despite being positively correlated with Mayo Risk Score results, the levels of AMA to 2-OADC proteins were not useful for predicting disease progression in individual patients with PBC. In addition, we found no significant differences in the levels of autoantibodies to 2-OADC proteins among patients with different histological stages of disease. Our results show that measurements of AMA by IF or by quantitative EIA methods with recombinant 2-OADC proteins are not useful parameters for predicting disease progression in patients with PBC.

Inhibition of PDC-E2 human combinatorial autoantibodies by peptide mimotopes

Immunohistochemical studies have shown that a unique immunoreactive molecule is present near the apical region of human biliary epithelial (BE) cells in patients with primary biliary cirrhosis (PBC). This can be visualized by confocal microscopy in PBC livers using a number of unique monoclonal antibodies to the E2 component of pyruvate dehydrogenase complex (PDC-E2), the autoantigen most commonly recognized by antimitochondrial antibodies (AMA). One such antibody, the murine mAb C355.1 was used to identify peptide mimotopes of PDC-E2 by screening a random dodecapeptide phage library ON 159.2 to identify the possible biochemical nature of this apical staining molecule. Out of 36 independent clones, 29 showed a common sequence and seven other sequences were singly represented. Three common amino acid motifs (SYP, TYVS and VRH) were found among these eight sequences. Similar to C355.1, the human combinatorial antibodies derived from a patient with PBC, SP1 and SP4, recognize the inner lipoyl domain of PDC-E2. However, when these antibodies are used to stain PBC BE cells, SP4 stains the apical region of PBC BE cells with high intensity whereas SP1 produces only cytoplasmic staining. Competitive inhibition of immunohistochemical staining using PDC-E2 specific human combinatorial antibodies SP1 and SP4 was performed using five of the above dodecapeptides. Interestingly, the peptides selected with C355.1 differentially inhibited the binding of SP1 and SP4 to PBC BE cells. Finally, rabbit sera raised against one such peptide (WMSYPDRTLRTS) stained BE cells from patients with PBC with a higher intensity than controls. Comparable data was obtained with immunoelectronmicroscopy. These data suggest that a molecular mimic of PDC-E2 is present at the external aspect of PBC BE cells.

IgE reactivity against a cross-reactive allergen in crustacea and mollusca: evidence for tropomyosin as the common allergen

BACKGROUND

Although cross-reactivity between mollusks and other crustaceans in shrimp-sensitive subjects has been reported, the mechanism of this allergenic cross-reactivity has not been studied in detail.

OBJECTIVE

To investigate this cross-reactivity in vitro, we have taken advantage of a complementary DNA that expresses tropomyosin, the immunodominant shrimp allergen.

METHODS

Serum IgE from nine patients with known anaphylaxis to shrimp and five normal volunteers were analyzed by immunoblotting against 13 distinct crustaceans and mollusks. As additional antigens, muscle preparations were isolated from grasshopper, cockroach, fruit fly, chicken, and mouse.

RESULTS

Sera from all patients, but not control subjects, reacted specifically with a 38 kd protein in all crustaceans and mollusks studied. In addition, 8 of 9 sera from patients, but from none of the normal control subjects, recognized proteins of various other molecular weights among the mollusk extracts studied. The 38 kd protein was identified as tropomyosin and was shown to share immunodominant epitopes among all species of crustaceans and mollusks tested by specific absorption studies. Moreover, sera from all nine subjects with shrimp allergy demonstrated IgE reactivities against grasshopper, cockroach, and fruit fly but not chicken or murine muscle.

CONCLUSION

The allergic epitopes on tropomyosin are conserved among invertebrates including not only shellfish but also insects. This latter observation suggests that persons sensitive to shrimp should undergo further study for potential cross-reactive inhalant or ingested insect sensitivity.

Random phage mimotopes recognized by monoclonal antibodies against the pyruvate dehydrogenase complex-E2 (PDC-E2)

Dihydrolipoamide acetyltransferase, the E2 component of the pyruvate dehydrogenase complex (PDC-E2), is the autoantigen most commonly recognized by autoantibodies in primary biliary cirrhosis (PBC). We identified a peptide mimotope(s) of PDC-E2 by screening a phage-epitope library expressing random dodecapeptides in the pIII coat protein of fd phage using C355.1, a murine monoclonal antibody (mAb) that recognizes a conformation-dependent epitope in the inner lipoyl domain of PDC-E2 and uniquely stains the apical region of bile duct epithelium (BDE) only in patients with PBC. Eight different sequences were identified in 36 phage clones. WMSYPDRTLRTS was present in 29 clones; WESYPFRVGTSL, APKTYVSVSGMV, LTYVSLQGRQGH, LDYVPLKHRHRH, AALWGVKVRHVS, KVLNRIMAGVRH and GNVALVSSRVNA were singly represented. Three common amino acid motifs (W-SYP, TYVS, and VRH) were shared among all peptide sequences. Competitive inhibition of the immunohistochemical staining of PBC BDE was performed by incubating the peptides WMSYPDRTLRTS, WESYPDRTLRTS, APKTYVSVSGMV, and AALWGVKVRHVS with either C355.1 or a second PDC-E2-specific mAb, C150.1. Both mAbs were originally generated to PDC-E2 but map to distinct regions of PDC-E2. Two of the peptides, although selected by reaction with C355.1, strongly inhibited the staining of BDE by C150.1, whereas the peptide APKTYVSVSGMV consistently inhibited the staining of C355.1 on biliary duct epithelium more strongly than the typical mitochondrial staining of hepatocytes. Rabbit sera raised against the peptide WMSYPDRTLRTS stained BDE of livers and isolated bile duct epithelial cells of PBC patients more intensively than controls. The rabbit sera stained all size ducts in normals, but only small/medium-sized ductules in PBC livers. These studies provide evidence that the antigen present in BDE is a molecular mimic of PDC-E2, and not PDC-E2 itself.

Use of a designer triple expression hybrid clone for three different lipoyl domain for the detection of antimitochondrial autoantibodies

The detection of antimitochondrial autoantibodies (AMAs) is critical in the diagnosis of primary biliary cirrhosis (PBC). However, conventional laboratory assays to detect AMA are dependent on the time-consuming method of immunofluorescence microscopy, a method often plagued by problems of nonspecificity. AMAs react against mitochondrial autoantigens including the E2 components of the pyruvate dehydrogenase complex (PDC-E2), the branched-chain 2-oxo-acid dehydrogenase complex (BCOADC-E2), and the 2-oxo-glutarate dehydrogenase complex (OGDC-E2). Interestingly, the immunodominant epitopes of PDC-E2, BCOADC-E2, and OGDC-E2 are all conformational lipoate binding sites, but antibodies against them do not cross-react. Although 80% to 90% of sera from patients with PBC react to PDC-E2, approximately 10% patients with PBC react only to BCOADC-E2 and/or OGDC-E2. We have taken advantage of our epitope-mapping studies of the E2 components of PDC, BCOADC, and OGDC, and constructed a "designer" hybrid clone, designated as pML-MIT3, that coexpresses the immunodominant epitopes within the three distinct lipoyl domains. We examined a total of 321 sera, including 186 sera from patients with PBC, to test the immunoreactivity of pMIT3. Of 186 sera from patients with PBC, 152 sera (81.7%) reacted with recombinant fusion protein of PDC-E2, whereas 171 sera (91.9%) showed positive reactivities when probed by immunoblotting against the recombinant fusion protein expressed from the pML-MIT3 clone. Of 34 PBC sera that did not react with recombinant PDC-E2, 18 sera contained BCOADC-E2-specific AMA and 1 serum possessed only OGDC-E2-specific AMA. We also developed an enzyme-linked immunosorbent assay (ELISA), using affinity-purified recombinant fusion protein of pML-MIT3 clone as the antigen source, to quantify specific AMAs in patients with PBC. None of the 135 control sera from patients with primary sclerosing cholangitis (PSC), chronic autoimmune hepatitis (CAH), systemic lupus erythematosus (SLE), or healthy volunteers showed significant reactivity against pML-MIT3 recombinant fusion protein in the ELISA assay. Our results indicate that an ELISA using recombinant, cloned autoantigen of pML-MIT3 is a powerful and very specific method for the detection of AMA.

Molecular aspects and the pathological basis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) has been considered to be a 'model auto-immune disease' for more than two decades. However, the underlying pathophysiology of PBC and the relationship with the associated serological abnormalities have been hitherto elusive. Beginning in 1987 with the cloning and subsequent identification of the mitochondrial autoantigens of PBC, progress has come rapidly and we can now sketch several potential pathogenic pathways through which disease occurs. More than 90% of patients with PBC produce autoantibodies to mitochondria, and the antoantigens involved have been identified as related components of the 2-oxo-acid dehydrogenase complexes (OADC), including the E2 subunits of the pyruvate dehydrogenase complex (PDC-E2), the branched chain 2-oxo-acid dehdrogenase complex and 2-oxo-glutarate dehydrogenase complex, Protein X and E1 alpha. The cDNAs of each of the E2 subunits of OADC have been cloned and characterized. Moreover, the epitopes of the antimitochondrial antibodies (AMA) have been mapped at the highly conserved lipoyl domain E2 subunits. The use of recombinant peptides produced by these clones has greatly facilitated the detection of AMA. In addition, nucleotide sequence analysis of PDC-E2 specific human monoclonals and combinatorial Fabs strongly suggests that these autoantibodies are derived from clonal selection of a restricted set of somatically mutated immunoglobulin germline genes. Most interestingly, however, the use of monoclonal reagents to PDC-E2 has demonstrated that there is an increased expression of either PDC-E2, or a cross-reactive molecule, on the luminal surface of biliary epithelial cells in patients with PBC. These data provide a scenario to explain the tissue specific pathology associated with PBC and several interesting underlying pathophysiological mechanisms.

Epitope mapping and reactivity of autoantibodies to the E2 component of 2-oxoglutarate dehydrogenase complex in primary biliary cirrhosis using recombinant 2-oxoglutarate dehydrogenase complex

Five different target mitochondrial autoantigens recognized by sera from patients with primary biliary cirrhosis (PBC) have been identified as subunits of the following 2-oxo acid dehydrogenase complexes: the pyruvate dehydrogenase complex (PDC), the branched chain 2-oxo acid dehydrogenase complex (BCOADC), and the 2-oxoglutarate dehydrogenase complex (OGDC). Unlike the E2 subunits of PDC (PDC-E2) and BCOADC (BCOADC-E2), the E2 subunits of OGDC (OGDC-E2) reactivity of PBC sera and the reactive epitope of OGDC-D2 have not hitherto been studied in detail. In this report, we took advantage of a recombinant fusion protein for OGDC-E2 to address these issues. Eighty of 268 (29.9%) PBC patient sera but none of the 45 controls reacted with recombinant OGDC-E2. The recombinant OGDC-E2 was judged to express the immunodominant epitope, because when sera from patients with PBC were preabsorbed with the recombinant fusion protein, such sera were depleted of reactivity against 48 kD OGDC-E2 when probed on beef heart mitochondria (BHM) but retained reactivity toward PDC-E2 and/or BCOADC-E2. Furthermore, affinity-purified PBC sera against recombinant OGDC-E2 reacted only with native OGDC-E2 and not with any other enzyme components of the 2-oxo acid dehydrogenase complex. Antimitochondrial autoantibodies (AMA) against OGDC-E2 included immunoglobulin (Ig)G2, IgG3 and IgM and the relative titers were as follows: IgG2 > IgG3 > IgM. Finally, using overlapping recombinant polypeptides, it was determined that a minimum of 81 amino acids (residues 67-147) corresponding to the lipoyl domain of OGDC-E2 are necessary for reactivity, suggesting that a conformational autoepitope is recognized by AMA. These data suggest that each of the 2-oxo acid dehydrogenase enzymes has distinct antigenicity despite their similarities in structure and function. The availability of recombinant OGDC-E2 autoantigen will allow the design of additional studies to further our understanding of the role of mitochondrial autoantigens in the pathogenesis of PBC.

Molecular biology of autoantigens in rheumatic diseases

The advent of molecular biologic techniques has provided new approaches that are of great utility to the study of autoimmune-mediated responses. In the past few years, there has been a remarkable accumulation of knowledge concerning the molecular identity and function of autoantigens, and further consolidation for the use of autoantibodies as diagnostic markers in clinical rheumatology. The understanding of basis methodologies in molecular biology applied to the study of autoantigens, in particular, techniques for cloning and analyzing genes that are important in rheumatic diseases, is valuable for both basic scientists and clinicians interested in diagnostic and prognostic markers of various connective tissue diseases.

Autoantibodies to BCOADC-E2 in patients with primary biliary cirrhosis recognize a conformational epitope

Primary biliary cirrhosis (PBC) is an autoimmune disease of liver associated with a unique serologic response to mitochondrial autoantigens. Many of the autoantigens recognized by autoantibodies in PBC are members of the 2-oxo-acid dehydrogenase complex. The two major autoantigens are the E2 component of the pyruvate dehydrogenase complex (PDC-E2) and the E2 component of the branched chain 2-oxo-acid dehydrogenase complex (BCOADC-E2). The autoantibody response to PDC-E2 has been mapped to one immunodominant epitope, which consists of both linear and conformational components. The presence of a single immunodominant epitope in PDC-E2 is unusual when contrasted to the immune response to autoantigens in other human autoimmune diseases. We have mapped the epitope recognized by antimitochondrial autoantibodies (AMA) specific to BCOADC-E2 in patients with PBC by taking advantage of the full-length bovine BCOADC-E2 complementary DNA (cDNA) and a series of expression clones spanning the entire molecule. Reactivity to the various expression clones was studied by immunoblotting, enzyme-linked immunosorbent assay (ELISA), as well as selective absorption of patient sera by expressed protein fragments. Autoantibodies to BCOADC-E2 map within peptides spanning amino acid residues 1 to 227 of the mature protein; our data demonstrate that the epitope is dependent on conformation and includes the lipoic acid binding region. However, only the full-length clone (amino acid residue 1 to 421) is sufficient to remove all detectable BCOADC-E2 reactivity. Moreover, the absence of lipoic acid on the recombinant polypeptides used in this study indicates that antibody binding to BCOADC-E2 is not dependent on the presence of lipoic acid.

Autoantibodies to BCOADC-E2 in patients with primary biliary cirrhosis recognize a conformational epitope

Primary biliary cirrhosis (PBC) is an autoimmune disease of liver associated with a unique serologic response to mitochondrial autoantigens. Many of the autoantigens recognized by autoantibodies in PBC are members of the 2-oxo-acid dehydrogenase complex. The two major autoantigens are the E2 component of the pyruvate dehydrogenase complex (PDC-E2) and the E2 component of the branched chain 2-oxo-acid dehydrogenase complex (BCOADC-E2). The autoantibody response to PDC-E2 has been mapped to one immunodominant epitope, which consists of both linear and conformational components. The presence of a single immunodominant epitope in PDC-E2 is unusual when contrasted to the immune response to autoantigens in other human autoimmune diseases. We have mapped the epitope recognized by antimitochondrial autoantibodies (AMA) specific to BCOADC-E2 in patients with PBC by taking advantage of the full-length bovine BCOADC-E2 complementary DNA (cDNA) and a series of expression clones spanning the entire molecule. Reactivity to the various expression clones was studied by immunoblotting, enzyme-linked immunosorbent assay (ELISA), as well as selective absorption of patient sera by expressed protein fragments. Autoantibodies to BCOADC-E2 map within peptides spanning amino acid residues 1 to 227 of the mature protein; our data demonstrate that the epitope is dependent on conformation and includes the lipoic acid binding region. However, only the full-length clone (amino acid residue 1 to 421) is sufficient to remove all detectable BCOADC-E2 reactivity. Moreover, the absence of lipoic acid on the recombinant polypeptides used in this study indicates that antibody binding to BCOADC-E2 is not dependent on the presence of lipoic acid.

Abnormal expression of the E2 component of the pyruvate dehydrogenase complex on the luminal surface of biliary epithelium occurs before major histocompatibility complex class II and BB1/B7 expression

Primary biliary cirrhosis (PBC) is a chronic autoimmune liver disease characterized histologically by nonsuppurative destructive cholangitis. Sera from patients with PBC react with a series of intramitochondrial enzymes with the immunodominant response directed against the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Recently, using tissue sections of late-stage PBC, we showed that there is increased expression in biliary epithelial cells of patients with PDC-E2 or a molecule cross-reactive with PDC-E2. Previous work has shown that biliary epithelial cells of patients with PBC express an increased amount of class II. To address the sequence of events in the evolution of PBC, we have focused our attention in this study on early biliary epithelial lesions. In particular, we have studied the liver of 22 female patients with PBC that was diagnosed as either stage I or stage II using both a mouse monoclonal antibody that has reactivity similar to human autoantibodies as well as a human Fab combinatorial prepared from the lymph node of a PBC patient. Tissues were simultaneously stained using antibodies to PDC-E2, class II, and BB1/B7. As a positive control, tissues from late-stage PBC were studied concurrently. By determining the order of expression among the three molecules, PDC-E2, class II, and BB1/B7, we report that the expression of PDC-E2 or a PDC-E2-like molecule on biliary duct epithelium of patients with PBC precedes the expression of BB1/B7 and major histocompatibility complex (MHC) class II molecules. The alteration of an autoantigen in biliary duct epithelium may be the earliest lesion in PBC.

Cadmium-induced DNA fragmentation is inhibitable by zinc in porcine kidney LLC-PK1 cells

DNA fragmentation was induced by the addition of cadmium (10 microM) to cultured LLC-PK1 cells, resulting in cell death. The cells were able to survive exposures of 10 microM cadmium without change in morphology, but most had rounded by 40 microM. Other metals tested such as Cu2+, Co2+, Ni2+, and Pb2+ had much lower ability to induce DNA fragmentation in LLC-PK1 cells under the same conditions as used for cadmium, indicating that the fragmentation seen in kidney cells is cadmium-specific. DNA fragmentation induced by 10 microM cadmium was completely inhibited using an equimolar concentration of a cell-permeant chelator specific for heavy metals, N,N,N',N'-tetrakis (2-pyridylmethyl)ethylenediamine. Furthermore, the apoptotic mechanism evoked by 10 microM cadmium was blocked by 50 microM zinc which when used alone has no capacity for DNA fragmentation.

Cloning, expression, and primary structure of Metapenaeus ensis tropomyosin, the major heat-stable shrimp allergen

Shrimp is a common cause of seafood hypersensitivity. To study the mechanism of seafood hypersensitivity at the molecular level, we have determined the primary structure of the major heat-stable allergen of shrimp by cloning, expression, nucleotide sequencing, and amino acid sequence determination of an IgE-reactive cDNA clone, Met e I, isolated from a Metapenaeus ensis expression library in lambda gt 11. We first constructed a cDNA library from the shrimp M. ensis in lambda gt 11. We then screened the library with sera from patients with hypersensitivity reactions to shrimp and identified a positive IgE-reactive clone, designated as Met e I. This cDNA was purified to homogeneity and subsequently expressed in the plasmid pGEX. Serum antibodies from patients with shrimp allergy demonstrated positive IgE reactivity by immunoblotting to a protein encoded by the clone Met e I; sera from nonallergic control subjects were not reactive. The nucleotide sequence of this cDNA clone revealed an open reading frame of 281 amino acid residues, coding for a protein of 34 kd. Comparison of the Met e I amino acid sequence with the Genbank database showed that Met e I is highly homologous to multiple isoforms of tropomyosin.

Heterogeneity of combinatorial human autoantibodies against PDC-E2 and biliary epithelial cells in patients with primary biliary cirrhosis

The polyclonal nature of antimitochondrial autoantibodies and the limited success of generating human monoclonal antibodies have made analysis of fine specificity and antibody heterogeneity difficult to define. The major autoantigen of primary biliary cirrhosis is the E2 component of the pyruvate dehydrogenase pathway (PDC-E2). To address the relative importance of the region(s) in the PDC-E2 inner lipoyl domain to antibody binding, we report herein detailed profiles of 12 PDC-E2-specific antigen-binding fragments, SP1 through SP12, derived by screening of a combinatorial immunoglobulin library (derived from a primary biliary cirrhosis patient) with full-length native PDC-E2. All antigen-binding fragments are IgG isotypes and include a similar number of lambda- and kappa-chains. The antigen-binding fragments react specifically to PDC-E2 with high affinity (kappa a = 10(-7) to 10(-10) mol/L-1) and recognize a conformational epitope in the inner lipoyl domain of PDC-E2. Furthermore, the antibodies demonstrate substantial heterogeneity in recognition of different recombinant PDC-E2 fragments and differential recognition patterns against mutant constructs of the human PDC-E2 inner lipoyl domain (amino acid residues 91 to 227). In addition, five of the antigen-binding fragment clones (SP1, 3, 4, 8 and 12) demonstrate different staining patterns on biliary epithelial cells of patients with primary biliary cirrhosis but not control liver disease; some antigen-binding fragments specifically stained the apical region of biliary epithelium, a pattern distinct from that of typical mitochondrial staining. The response to the inner lipoyl domain is not, however, monospecific, and there is much more heterogeneity in fine specificity than could be accounted for by arbitrary reshuffling of variable immunoglobulin heavy and light chains into unnatural combinations.

Nucleotide sequence analysis of natural and combinatorial anti-PDC-E2 antibodies in patients with primary biliary cirrhosis. Recapitulating immune selection with molecular biology

We have analyzed at the nucleotide level the variable region gene sequences of five human mAbs and five recombinant Fab fragments derived from the mesenteric lymph nodes of patients with primary biliary cirrhosis. Both mAbs and Fabs were monospecific for dihydrolipoamide acetyltransferase, the E2 subunit of the pyruvate dehydrogenase complex, which has been shown to be the major autoantigen of primary biliary cirrhosis. We found that although the mAbs, mainly of the IgM isotype, were encoded by a diverse array of VH and VL gene segments either as direct copies of germline genes or somatically mutated, the recombinant IgG Fabs expressed clonally related heavy chains displaying a high number of somatic mutations that very likely occurred in the context of Ag selection. Combinatorial pairing of clonally related heavy chains with highly homologous light chains suggests that the IgG anti-pyruvate dehydrogenase complex repertoire of primary biliary cirrhosis patients is the result of the clonal expansion of a restricted set of B cells.

Nucleotide sequence analysis of natural and combinatorial anti-PDC-E2 antibodies in patients with primary biliary cirrhosis. Recapitulating immune selection with molecular biology

We have analyzed at the nucleotide level the variable region gene sequences of five human mAbs and five recombinant Fab fragments derived from the mesenteric lymph nodes of patients with primary biliary cirrhosis. Both mAbs and Fabs were monospecific for dihydrolipoamide acetyltransferase, the E2 subunit of the pyruvate dehydrogenase complex, which has been shown to be the major autoantigen of primary biliary cirrhosis. We found that although the mAbs, mainly of the IgM isotype, were encoded by a diverse array of VH and VL gene segments either as direct copies of germline genes or somatically mutated, the recombinant IgG Fabs expressed clonally related heavy chains displaying a high number of somatic mutations that very likely occurred in the context of Ag selection. Combinatorial pairing of clonally related heavy chains with highly homologous light chains suggests that the IgG anti-pyruvate dehydrogenase complex repertoire of primary biliary cirrhosis patients is the result of the clonal expansion of a restricted set of B cells.

Immunocytochemical localization of neuropeptide F-immunoreactivity in the circumoesophageal ganglia of the gastropod mollusc, Helix aspersa using electron microscopy

Neuropeptide F (NPF)-immunoreactivity has been localized by electron microscopy in the central nervous system of the gastropod mollusc, Helix aspersa using a region-specific antiserum in conjunction with post-embedding immunogold labelling. The specific antiserum employed, designated NPF3, was raised to a synthetic N-terminal fragment of H. aspersa NPF. Gold-labelling revealed that NPF-immunoreactivity was found almost exclusively over the contents of dense-cored secretory vesicles within nerve axons in both cerebral and subesophageal ganglia. Double-labelling of NPF and FMRFamide demonstrated no apparent co-localization in the paired cerebral ganglia. Instead, immunoreactivities of the two neuropeptides were found to have distinct locations within the ganglia. These findings suggest that NPF may be an important neuroregulator in H. aspersa and that in the cerebral ganglia it may be anatomically-distinct from FMRFamide and related peptides.

Immunocytochemical distribution of neuropeptide F (NPF) in the gastropod mollusc, Helix aspersa, and in several other invertebrates

The distribution of neuropeptide F (NPF) immunoreactivity in the snail, Helix aspersa, has been demonstrated by immunocytochemistry using 2 region-specific antisera. One, designated NPF3, was raised against a synthetic N-terminal fragment of Helix aspersa NPF; the other, designated PP221, was raised against the C-terminal hexapeptide amide of mammalian pancreatic polypeptide (PP) but cross-reacts fully with the analogous C-terminal region of Helix aspersa NPF. The distribution of NPF immunoreactivity has also been compared with that of FMRFamide using alternate serial sections of Helix aspersa ganglia. Results showed that NPF immunoreactivity was abundant and widespread in the central and peripheral nervous systems and the pattern of immunostaining obtained using both region-specific antisera was similar. Likewise, immunocytochemistry of neural tissues of a congeneric species, Helix pomatia, and 2 prosobranch gastropods, Buccinum undatum and Littorina littorea, produced similar staining patterns with both antisera. However, in the cephalopod mollusc, Loligo vulgaris, and the cestode, Moniezia expansa, positive immunostaining was only obtained with the C-terminal PP antiserum. Immunostaining of alternate serial sections of Helix aspersa ganglia with NPF3, and an antiserum raised to FMRFamide, showed that while a few neurones were immunoreactive with one antiserum only, in the majority, both immunoreactivities were co-localised. NPF thus appears to be an important neuropeptide of widespread distribution in Helix aspersa and the differential immunocytochemical staining obtained using the 2 region-specific antisera would suggest a high degree of primary structural conservation within the gastropod molluscs, but lack of conservation of the N-terminal region of the peptide in other invertebrate groups.

Quantitation and chromatographic characterisation of neuropeptide F(NPF) immunoreactivity in molluscan nervous tissue using region-specific antisera

Neuropeptide F (NPF) immunoreactivity has been quantified in extracts of the central nervous system from four gastropod (Helix aspersa, Buccinum undatum, Littorina littorea, and Patella vulgaris) and two bivalve (Mytilus edulis and Pecten maximum) molluscs using two region-specific radioimmunoassays. The first employed an antiserum, NPF3, raised to a synthetic N-terminal fragment of H. aspersa NPF and the second employed an antiserum, PP221, raised to the synthetic C-terminal hexapeptide amide of mammalian pancreatic polypeptide which fully cross-reacts with the analogous region of H. aspersa NPF. NPF immunoreactivity was detected in acidified ethanolic brain extracts of the four gastropod molluscs by both antisera. However, only the C-terminally directed antiserum detected immunoreactivity in brain extracts of the two bivalve molluscs. Reverse-phase HPLC analysis of brain extracts from B. undatum and L. littorea resolved a single NPF immunoreactive peptide which was more hydrophobic than natural H. aspersa NPF chromatographed under the same conditions. Gel permeation chromatography of these NPF immunoreactive peptides indicated that they were of a similar molecular mass to that of H. aspersa NPF. These data suggest that NPF is widely distributed in molluscs with a high degree of structural conservation of N- and C-terminal regions within the gastropod molluscs but significant structural differences within the N-terminal regions of analogous peptides in bivalves.

Evaluation of possible histamine release from human peripheral blood cells using an enzyme immunoassay (HRT) with components of intravenous catheters

The HRT Assay was evaluated for its capacity to measure histamine release from blood basophils following the introduction of extracts from catheters made of Aquavene or silicone. Blood samples were collected from twenty-one volunteers of the University of California, Davis campus and from seven individual who had experienced a systemic event during the insertion of catheters made from Aquavene. None of the blood samples released histamine in quantities that would be anticipated in an anaphylactic or anaphylactoid reaction when challenged with the extracts; all released histamine when challenged with polymyxin B, used as a positive control. Based upon these results, none of the components of either the Aquavene-based or silicone-based catheters are thought to cause a histamine-associated reaction in subjects. This assay proved to be both expedient and reliable in its determination of the release of histamine from blood basophils.

Comparative metabolism and structure of BCKD-E2 in primary biliary cirrhosis

The identification and cloning of the mitochondrial autoantigens in primary biliary cirrhosis (PBC) have provided new clues in disease pathogenesis. The two major autoantigens are the E2 subunits of pyruvate dehydrogenase and branched-chain ketoacid dehydrogenase (BCKD). Interestingly, one of these complexes, BCKD-E2, is already well known to clinical medicine based on its association with genetic mutations in maple syrup urine disease (MSUD). Patients with this disease have an inability to metabolize branched-chain amino acids. In the present study, we have taken advantage of the known sequence of BCKD-E2 from normal humans, and addressed the issue of whether there is an altered autoantigen sequence in hepatocytes of individuals with primary biliary cirrhosis. In particular, we examined both the leader sequence and the B-cell immunodominant epitope, the lipoic acid domain. In addition, because patients with PBC have autoantibodies to the BCKD-E2 complex, we have quantitated plasma levels of alpha-ketoacids potentially affected in maple syrup urine disease. These include pyruvic acid (PY), phenylpyruvic acid (PP), alpha-ketoisocaproic acid (KIC) alpha-ketoisovalerate (KIV) and alpha-keto-beta-methylvaleric acid (KMV). The levels of these alpha-ketoacids were compared in patients with primary sclerosing cholangitis and normal volunteers. The sequence of BCKD-E2 obtained from PBC hepatocytes showed homology with normal BCKD. Further studies of autoantigen structure and sequence are clearly indicated, including those involved in mitochondrial transport and localization. Finally, we noted a statistically significant increase in all plasma alpha-ketoacids except alpha-keto-beta-methylvaleric acid in PBC patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular mimicry in primary biliary cirrhosis. Evidence for biliary epithelial expression of a molecule cross-reactive with pyruvate dehydrogenase complex-E2

Sera from patients with primary biliary cirrhosis (PBC) react with enzymes of the 2-oxo dehydrogenase pathways, particularly PDC-E2. These enzymes are present in all nucleated cells, yet autoimmune damage is confined to biliary epithelial cells. Using a panel of eight mouse monoclonal antibodies and a human combinatorial antibody specific for PDC-E2, we examined by indirect immunofluorescence and confocal microscopy sections of liver from patients with PBC, progressive sclerosing cholangitis, and hepatocarcinoma. The monoclonal antibodies gave typical mitochondrial immunofluorescence on biliary epithelium and on hepatocytes from patients with either PBC, progressive sclerosing cholangitis, or hepatocarcinoma. However, one of eight mouse monoclonal antibodies (C355.1) and the human combinatorial antibody reacted with great intensity and specificity with the luminal region of biliary epithelial cells from patients with PBC. Simultaneous examination of these sections with an antiisotype reagent for human IgA revealed high IgA staining in the luminal region of biliary epithelial cells in patients with PBC. IgG and IgA antibodies to PDC-E2 were detected in the bile of patients with PBC but not normal controls. We believe that this data may be interpreted as indicating that a molecule cross-reactive with PDC-E2 is expressed at high levels in the luminal region of biliary epithelial cells in PBC.

Combinatorial autoantibodies to dihydrolipoamide acetyltransferase, the major autoantigen of primary biliary cirrhosis

mRNA from a regional lymph node of a patient with primary biliary cirrhosis (PBC) was used to construct a combinatorial immunoglobulin library in the lambda phage vector system. Six human monoclonal IgG Fab clones (LC1-LC6) specific for the major autoantigen of PBC--dihydrolipoamide acetyltransferase, the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2)--were isolated, appearing at a frequency of 0.01% in the combinatorial immunoglobulin library. These Fab clones recognize human PDC-E2 with high affinity (Ka = 10(-7)-10(-9) M-1). Using both immunoblotting and ELISA, LC1-LC6 showed little cross-reactivity to any of the other autoantigens commonly recognized by PBC sera or to other antigens commonly recognized by PBC sera or to other antigens such as histone, calf thymus DNA, and bovine serum albumin. The Fab monoclonal antibodies show a typical anti-mitochondrial staining pattern in HEp-2 cells but react strongly with the luminal aspect of biliary epithelial cells of patients with PBC. Our results demonstrate that a recombinant combinatorial immunoglobulin library can be used to isolate high-affinity Fabs against a specific autoantigen. Such reagents will facilitate the analysis of immunoglobulin gene structure, idiotype, and antigen-antibody interactions in autoimmune disease.

Chromosome localization and RFLP analysis of PDC-E2: the major autoantigen of primary biliary cirrhosis

Patients with primary biliary cirrhosis are well known for the presence of titer antibodies against dihydrolipoamide acetyltransferase, the E2 subunit of the pyruvate dehydrogenase complex. We have taken advantage of a cDNA probe for dihydrolipoamide acetyltransferase to explore the possibility of polymorphism of the E2 subunit by probing genomic DNA from 38 patients with primary biliary cirrhosis and 26 healthy controls. To detect restriction fragment length polymorphism, DNA was digested with ten specific restriction enzymes that often detect polymorphism, including Bam HI, Bgl II, Eco RI, Hind III, Hinf I, Msp I, Pst I, Pvu II, Rsa I and Taq I. A Taq I polymorphism was found in 19 of 38 patients with PBC and 6 of 26 normal controls. In addition, using fluorescence in situ hybridization, the gene for dihydrolipoamide acetyltransferase was mapped on human chromosome 11 band q23.1. Interestingly, this region of the long arm of chromosome 11 is often associated with cytogenetic abnormalities, including translocations.

Immunoglobulin genes in autoimmunity

The contribution of V germline genes and somatic mutation as well as the mechanism governing expression of the various V family genes in response to self-antigens are still unknown. Thus, we are still far from understanding the contribution and role of the B cell repertoire in human autoimmunity. Much of our current data on autoantibody gene repertoire are derived from laboratory generated hybridomas or animal model of autoimmune diseases. These may not reflect the human situation. In contrast, very few human autoantibodies with defined specificities have been structurally and genetically analyzed. In the future, meaningful data, perhaps from direct cloning and sequencing of autoantibodies derived from patients with autoimmune diseases, will be necessary to resolve issues in autoantibody repertoire usage. In this article, the prominent features of the human Ig repertoire, the usage of germline genes in autoantibodies, identifications of somatic mutations among autoantibodies and current data supporting either restricted or nonrestricted Ig gene usage and idiotypic expression among autoantibodies in several well-studied autoimmune diseases including systemic lupus erythematosus and rheumatoid arthritis are discussed.

Characterization and epitope mapping of human monoclonal antibodies to PDC-E2, the immunodominant autoantigen of primary biliary cirrhosis

Further to define the epitopes of PDC-E2, the major autoantigen in primary biliary cirrhosis (PBC), we have developed and characterized five human monoclonal antibodies. These antibodies were derived by fusing a regional hepatic lymph node from a patient with PBC with the mouse human heterohybrid cell line F3B6. Previous studies of epitope mapping of PDC-E2 have relied on whole sera and have suggested that the immunodominant epitope lies within the inner lipoyl domain of the molecule. However, selective absorption studies using whole sera and a series of overlapping recombinant peptides of PDC-E2 have suggested that the epitope may also include a large conformational component. Moreover, several laboratories have suggested that autoantibodies against the 2-oxo acids dehydrogenase autoantigens are cross-reactive. The five monoclonal antibodies generated included three IgG2a and two IgM antibodies and were studied for antigen specificity using recombinant PDC-E2, recombinant BCKD-E2, histone, dsDNA, IgG (Fc), collagen and a recombinant irrelevant liver specific control, the F alloantigen. The antibodies were also used to probe blots of human, bovine, mouse and rat mitochondria. Finally, fine specificity was studied by selective ELISA and absorption against overlapping expressing fragments of PDC-E2. All five monoclonals, but none of the other mitochondrial autoantigens were specific for PDC-E2. In fact, although affinity purified antibodies to PDC-E2 from patients with PBC cross-reacted with protein X, the human monoclonals did not, suggesting that protein X contains an epitope distinct from that found on PDC-E2. Additionally, all three IgG2 monoclonals recognized distinct epitopes within the inner lipoyl domain of PDC-E2.

Antimitochondrial antibodies in kindreds of patients with primary biliary cirrhosis: antimitochondrial antibodies are unique to clinical disease and are absent in asymptomatic family members

The 2-oxo-acid dehydrogenase family of enzymes have been identified as the major mitochondrial autoantigens of primary biliary cirrhosis. Using immunoblotting, enzyme-linked immunosorbent assay and enzyme inhibition with both purified mitochondrial proteins and recombinant autoantigens, we have studied family members and spouses of patients with primary biliary cirrhosis for the presence of antimitochondrial antibodies. Antimitochondrial antibodies and other common autoantigens were also tested for by indirect immunofluorescence. This study included 27 index patients with primary biliary cirrhosis, 15 spouses and 48 first- and second-degree relatives. Overall, 7 relatives (11%) were positive for autoantibodies to nuclear and cytoplasmic antigens by indirect immunofluorescence against mouse liver and stomach sections. However, with immunofluorescence, the reactivity strictly paralleled that of antimitochondrial antibodies in only one of these (1:640)--a sibling with mild pruritus and a liver biopsy specimen diagnostic of primary biliary cirrhosis despite normal levels of serum alkaline phosphatase. In addition, one of the mothers, who had a history of sarcoidosis, was positive by immunoblotting for antibodies to the E2 subunit of the pyruvate dehydrogenase complex and protein X. All other relatives were negative for all of the assays. Antibodies to neither the 2-oxo-acid dehydrogenase enzymes nor the recently proposed family of naturally occurring mitochondrial antibodies were found in spouses or healthy relatives. Three other first-degree relatives suffered from liver disease: two died (one from primary biliary cirrhosis and the other from an unknown type of liver disease) and one (a sibling with primary biliary cirrhosis) was unavailable for testing. Our results are consistent with a familial predisposition to primary biliary cirrhosis.(ABSTRACT TRUNCATED AT 250 WORDS)

The primary structure of neuropeptide F (NPF) from the garden snail, Helix aspersa

Neuropeptide F (NPF), originally isolated from the sheep tapeworm, Moniezia expansa, consists of 39 amino acid residues terminating in a phenylalaninamide. An analogous neuropeptide has been isolated and sequenced from extracts of circumoesophageal ganglia of the garden snail, Helix aspersa. This neuropeptide exhibits partial primary structural similarity to members of the vertebrate neuropeptide Y (NPY)/pancreatic polypeptide (PP) superfamily. NPF is thus of widespread occurrence in the nervous systems of invertebrates from different phyla and may represent the phylogenetic precursor of the vertebrate NPY/PP superfamily.

Immunochemical characterisation of tachykinin immunoreactivity in the nervous system of the garden snail, Helix aspersa

1. Circumoesophageal ganglia and foot muscle of the garden snail, Helix aspersa, were subjected to immunocytochemistry using antisera to the tachykinins, substance P (SP), neurokinin A (NKA), kassinin (KAS) and eledoisin (ELE). 2. Immunoreactivity in neuronal somata and fibres was detected only with the SP antiserum. 3. SP and NKA radioimmunoassays were performed on extracts of circumoesophageal ganglia. In common with immunocytochemistry, immunoreactivity was only detected with the SP antiserum. 4. Gel permeation chromatography of extracts resolved a single peak of immunoreactivity eluting slightly later than synthetic mammalian SP. Reverse-phase HPLC of immunoreactive fractions resolved two immunoreactive peptides representing oxidised and reduced forms of a single peptide. 5. These data suggest that the nervous system of H. aspersa contains a single tachykinin with C-terminal structural characteristics similar to mammalian SP.

Use of designer recombinant mitochondrial antigens in the diagnosis of primary biliary cirrhosis

The appearance of autoantibodies against mitochondria in patients with primary biliary cirrhosis has been known for more than 25 yr. In the past, based on the biochemical complexity of the mitochondrion and the use of crude extracts for immunodiagnosis, a degree of nonspecificity in assaying for antibodies to mitochondria has been present. This problem has been largely circumvented by the cloning of the mitochondrial antigens and the identification of the E2 subunits of the pyruvate dehydrogenase complex and the branched chain 2-oxo-acid dehydrogenase complex as the major and immunodominant autoantigens of primary biliary cirrhosis. More than 90% of patients with primary biliary cirrhosis have been shown to react with one or both of these enzymes using either recombinant antigen or purified native protein. Approximately 10% of patients recognize only E2 subunits of branched chain 2-oxo-acid dehydrogenase complex and not pyruvate dehydrogenase complex. Such patients would be missed by diagnostic assay that has a low sensitivity to antibodies against E2 subunits of branched chain 2-oxo-acid dehydrogenase complex. The use of recombinant and biochemically pure antigens has permitted structural and conformational analysis of epitope mapping. We have taken advantage of the antigenic mapping studies of both primary biliary cirrhosis and branched chain 2-oxo-acid dehydrogenase complex E2 subunits and designed a molecule that expresses the immunodominant epitopes of both. Using this dual-headed molecule that coexpresses the epitope of two different antigens, we report herein a sensitive and reproducible assay for antibodies to mitochondria in patients with primary biliary cirrhosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative immunoreactive profiles of Japanese and American patients with primary biliary cirrhosis against mitochondrial autoantigens

Primary biliary cirrhosis (PBC) has been described among various ethnic and racial populations in all parts of the world. However, the incidence and prevalence of PBC varies considerably in different geographic areas. It has the highest frequency in Northern Europe, is considerably lower in Japan and still lower in other parts of Asia. There has not hitherto been a detailed immunological profile of antimitochondrial antibodies according to geographic region. We have used recombinant or purified preparations from the 2-oxo-acid dehydrogenase enzyme complexes, the major mitochondrial autoantigens in PBC (PDC-E2, BCOADC-E2, OGDC, protein X and PDC-E1 alpha) to compare the reactivity of sera from either similarly staged sera from Japanese (n = 23) or American-Caucasian patients (n = 39) with PBC. In all cases, the first available sera following diagnosis was selected. Interestingly, only 65% of Japanese patients reacted by ELISA with PDC-E2 compared with more than 95% of the North American group. Moreover, the level of enzyme-inhibitory antibodies to PDC was lower in the Japanese. Our findings prompt the need for characterization of specific susceptibility genes and environmental factors in various parts of the world to clarify the etiology of PBC.

The identification and cloning of the murine genes encoding the liver specific F alloantigens

The liver specific F alloantigen is a highly conserved abundant protein found in hepatic cytoplasm; smaller amounts are detected in renal tubule cells and the perikaryon cells of the central nervous system. Although the biological function of the F alloantigen is unknown, the immune response to F has been extensively studied as a murine model of tolerance and autoimmunity. Murine F exists in two allelic forms, designated F type 1 and type 2, each of approximately 43 kDa. The immune response to the allotypic form is restricted to mouse strains of I-Ak. Responding strains immunized with allotypic F break tolerance and produce precipitating antibody that reacts with both allelic forms, i.e., immunogen and self. Thus an autoantibody is produced. Using the previously isolated rat F cDNA as a probe, we report the cloning and sequencing of the two murine F allotypes. These two alleles are nearly homologous except at the extremes of the coding sequence. There are a number of regions within the F sequence that are similar to peptides that interact specifically with I-Ak. In particular, there is a sequence near the carboxy terminus, where the two allotypes differ, that has homology to the I-Ak restricted malarial antigen peptide of the ring-infected erythrocyte surface antigen (RESA).