Regulation of N- and L-type Ca2+ channels in adult frog sympathetic ganglion B cells by nerve growth factor in vitro and in vivo

To examine mechanisms responsible for the long-term regulation of Ca2+-channels in an adult neuron, changes in whole cell Ba2+ current (IBa) were examined in adult bullfrog sympathetic ganglion B cells in vitro. Cells were cultured at low density in defined, serum free medium. After 15 days, total IBa was similar to the initial value, whereas IBa density was reduced by approximately 36%, presumably due to an increase in neuronal surface area. By contrast, IBa density remained constant after 6-15 days in the presence of murine beta-NGF (200 ng/ml), and total IBa was almost doubled. Inclusion of cytosine arabinoside (Ara-C; 10 microM) to inhibit proliferation of nonneuronal cells, did not affect the survival of neurons in the absence of nerve growth factor (NGF) nor did it attenuate IBa. Ara-C did not prevent the effect of NGF on IBa. There were three independent components to the action of NGF; during 6-9 days, it increased omega-conotoxin-GVIA-sensitive N-type IBa (IBa,N); increased nifedipine-sensitive L-type IBa (IBa,L) and decreased inactivation of the total Ba2+ conductance (gBa). The latter effect involved a selective decrease in the amplitude of one of the four kinetic components that describe the inactivation process. Total IBa was also 55.8% larger than control in the somata of B cells acutely dissociated from leopard frogs that had received prior subcutaneous injections of NGF. By contrast, injection of NGF antiserum decreased total IBa by 29.4%. There was less inactivation of gBa in B cells from NGF-injected animals than in cells from animals injected with NGF antiserum (P < 0.001). These data suggest that NGF-like molecule(s) play(s) a role in the maintenance of IBa in an adult amphibian sympathetic neuron; the presence of NGF may allow the neuron to maintain a constant relationship between cell size and current density. They also show that IBa inactivation in an adult neuron can be modulated in a physiologically relevant way by an extracellular ligand.

[Histopathologic and immunochemical changes in Sjögren's syndrome]

To research into the causes of sjögren's syndrome, we investigated the lacrimal gland tissues of 6 cases of sjogren's syndriome by using electronmicroscopy and immunochemical methods. The results revealed that at the early stage the lacrimal gland cells showed degeneration, irregular arrangement and many intracellular vacuoles. At the middle stage, some lymphocytes infliltrated into the gland tissues. And at the advanced stage, lymphocytes and collagenous fibers were there in substitution of gland cells.

Influence of activity and dietary energy on broiler performance, carcase yield and sensory quality

1. A total of 2560 male and female Ross broilers were raised to 42 days of age in a 2 X 2 treatment factorial arrangement experiment to investigate the influence of different degrees of physical activity and dietary energy on broiler performance, abdominal fat content, carcase yield and sensory quality. 2. Vertical fans were used to force the treatment birds to walk 3 to 4 times as far as the normal activity birds: birds were fed a normal and a high energy diet (12.55 compared with 13.81 MJ ME/kg) with the same energy/protein, energy/lysine and energy/methionine + cystine ratios. 3. High activity birds had greater body weight (+4.1%), food intake (+5.1%) and ME intake (+5.1%) than normal activity birds. Birds receiving high energy diet had a lower food conversion and food intake than birds receiving normal energy diet. There were no significant differences in body weight or ME intake between birds with different diets. 4. Slaughter yields, both absolute and relative to live body weight, were affected by activity or dietary energy to varying degrees. Breast meat was increased with more activity. The absolute weight of abdominal fat was independent of activity and in males the relative weight of abdominal fat was decreased in high activity birds. 5. Different degrees of activity and dietary energy had only minor influences on broilers sensory quality.

Antibodies as tools to study the structure of membrane proteins: the case of the nicotinic acetylcholine receptor

The nicotinic acetylcholine receptor is the prototype of the ionotropic receptor superfamily of proteins, which includes the closely related gamma- aminobutyric acid type A and glycine receptors, and more distantly related serotonin type-3 and glutamate receptors. Several models of the transmembrane topology of the nicotinic acetylcholine receptor subunits were originally proposed based on hydropathy analysis of their deduced amino acid sequences. Antibodies specific to different epitopes of the nicotinic acetylcholine receptor have proven to be valuable probes for examining the validity of those models. Despite important caveats, a viable model for the transmembrane structure and functional topology of the nicotinic acetylcholine receptor subunits has been obtained from the antibody mapping studies. This model, and the associated methodological shortcomings and obstacles that were overcome in the process of its formulation, can legitimately be extended to other members of the ionotropic receptor superfamily and to other membrane proteins as well.

[Effect of tetrandrine on intraacinar pulmonary arterial structural remodelling and pulmonary hypertension]

Rat's pulmonary hypertension was induced by a single subcutaneous injection of monocrotaline. The influences of tetrandrine (Tet) upon the structure of intraacinar pulmonary arteries (IAPA) was studied by light and electron microscopy. The results indicated that Tet reduced the thickness of IAPA medial membrane, the ratio of the thickness of IAPA medial membrane to the diameter of IAPA, the number of circular muscular artery and partially muscular artery about 16.4%, 30.5%, 24.3% and 16.4% respectively, and Tet increased the number of nonmuscular artery about 24.7%. It also decreased the degeneration of IAPA, collagen of medial membrane, prolife-ration and myoid differentiation of the pericyte, and it increased the number of IAPA. The authors discussed why Tet caused such changes.

Nif- phenotype of Azotobacter vinelandii UW97. Characterization and mutational analysis

We have identified the molecular basis for the nitrogenase negative phenotype exhibited by Azotobacter vinelandii UW97. This strain was initially isolated following nitrosoguanidine mutagenesis. Recently, it was shown that this strain lacks the Fe protein activity, which results in the synthesis of a FeMo cofactor-deficient apodinitrogenase. Activation of this apodinitrogenase requires the addition of both MgATP and wild-type Fe protein to the crude extracts made by A. vinelandii UW97 (Allen, R.M., Homer, M.J., Chatterjee R., Ludden, P.W., Roberts, G.P., and Shah, V.K. (1993) J. Biol. Chem. 268 23670-23674). Earlier, we proposed the sequence of events in the MoFe protein assembly based on the biochemical and spectroscopic analysis of the purified apodinitrogenase from A. vinelandii DJ54 (Gavini, N., Ma, L., Watt, G., and Burgess, B.K. (1994) Biochemistry 33, 11842-11849). Taken together, these results imply that the assembly process of apodinitrogenase is arrested at the same step in both of these strains. Since A. vinelandii DJ54 is a delta nifH strain, this strain is not useful in identifying the features of the Fe protein involved in the MoFe protein assembly. Here, we report a systematic analysis of an A. vinelandii UW97 mutant and show that, unlike A. vinelandii DJ54, the nifH gene of A. vinelandii UW97 has no deletion in either coding sequence or the surrounding sequences. The specific mutation responsible for the Nif- phenotype of A. vinelandii UW97 is the substitution of a non-conserved serine at position 44 of the Fe protein by a phenylalanine as shown by DNA sequencing. Furthermore, oligonucleotide site-directed mutagenesis was employed to confirm that the Nif- phenotype in A. vinelandii UW97 is exclusively due to the substitution of the Fe protein residue serine 44 by phenylalanine. By contrast, replacing Ser-44 with alanine did not affect the Nif phenotype of A. vinelandii. Therefore, it seems that the Nif- phenotype of A. vinelandii UW97 is caused by a general structural disturbance of the Fe protein due to the presence of the bulky phenylalanine at position 44.

[Effect of tetrandrine on pulmonary hypertension induced by monocrotaline in rats]

The effects of Tetrandrine (Tet) on intraacinous pulmonary arteries (IAPA) and bemodynamics were studied by means of a rat pulmonary hypertension model induced by monocrotaline. The results showed that Tet could reduce the contractive pressure of pulmonary artery, right ventricle and right atrium of heart by 28.0%, 28.3%, and 31.5% respectively. It could also decrease the vascular degeneration of endoepithelial cells of IAPA, the endoepithelial subcavity, the collagens of medial membrane and the numbers of smooth muscles of IAPA.

Binding of monoclonal antibodies against the carboxyl terminal segment of the nicotinic receptor delta subunit suggests an unusual transmembrane disposition of this sequence region

Monoclonal antibodies (mAbs) specific for the carboxyl terminal region of the delta subunit of Torpedo nicotinic acetylcholine receptor (AChR), derived from mice immunized with AChR or a synthetic carboxyl terminal sequence of the delta subunit (C delta-mAbs), were used to determine the transmembrane disposition of their epitope(s) by immunoelectron microscopy, using AChR-rich postsynaptic membrane fragments from Torpedo electroplax. Some C delta-mAbs recognized only the cytoplasmic side of the membranes, some both sides to a similar extent, and others bound mostly, but not exclusively, to the cytoplasmic side. Binding of C delta-mAbs to the membranes was specifically blocked by synthetic peptides containing the carboxyl terminal region of the delta subunit. Control anti-AChR mAbs specific for the alpha or the delta subunits, whose epitopes have known transmembrane topology, uniquely recognized the expected side of the postsynaptic membrane. Residues involved in C delta-mAb binding were identified using single residue substituted peptide analogues of the sequence delta 481-501. All C delta-mAbs recognized epitopes within the same sequence segment, delta 485-493, at the carboxyl terminal of the AChR delta subunit. These results suggest that the delta subunit of the AChR might have alternative conformations, leading to exposure of the same sequence region on the extracellular or the cytoplasmic surface. Several Pro residues are present in this region. The alternative cis or trans conformation of one or more of them might result in different folding patterns of the carboxyl terminal sequence of the delta subunit, as described for a viral protein [Liddington, R. C., Yan, Y., Moulai, J., Sahli, R., Benjamin, T. L., & Harrison, S. C. (1991) Nature 354, 278-284.

Clustering of B and T epitopes within short sequence regions of the nicotinic acetylcholine receptor

The epitope repertoire of B cells, due to their selective ability to process their specific antigen and the potential bias imposed on the resulting peptides by the surface immunoglobulins bound to the antigen, may influence the T-helper repertoire. Immunization of C57B1/6 mice with Torpedo acetylcholine receptor (TAChR) causes experimental autoimmune myasthenia gravis (EAMG). Anti-TAChR CD4+ cells recognize epitopes within three sequence regions of the TAChR alpha subunit ('dominant epitopes'). Immunization of mice with denatured or synthetic TAChR antigens sensitizes CD4+ cells to other TAChR sequence regions ('cryptic epitopes'). We investigated here whether clustering of B and T epitopes within the same short sequence segments occurs during the anti-TAChR response, as previously described for the response to hexogenous antigens unrelated to homologous self proteins. Twelve 19-20 residue synthetic sequences of the TAChR alpha, gamma and delta subunits, containing dominant or cryptic CD4+ epitopes for C57B1/6 mice, were tested for ability to induce anti-peptide antibody production. C57B1/6 mice were immunized with the individual peptides. Ten peptides stimulated antibody production. Therefore > 80% of these short TAChR sequences also contain B epitopes. Therefore also in the anti-TAChR response leading to EAMG T and B cell epitopes frequently reside within the same short sequence segment.

Overexpression of HER2/neu oncogene in pancreatic cancer correlates with shortened survival

For the purpose of determining the prognostic significance of HER2/neu oncogene in pancreatic and ampullary cancers, 21 pancreatic cancers of ductal origin and six cancers of the ampulla of Vater were studied immunohistochemically using the monoclonal antibody (MAb) CB11, specifically reactive with HER2/neu product. Staining of the epithelium of the normal duct and acini was negative or weakly positive. Moderately and strongly positive reactions indicated the overexpression of this gene, and were found in 10 of 21 (47.6%) pancreatic cancers of ductal origin and in 2 of 6 (33.3%) ampullary adenocarcinomas. Overexpression of HER2/neu was closely and inversely related to the survival of the patients with pancreatic cancer of ductal origin: 19.1 +/- 11.7 mo for those not overexpressing vs 7.3 +/- 3.8 mo for the overexpressors (p < 0.01). Among the pancreatic cancer group, 11 patients underwent cancer resection. The average survival for the 7 with nonoverexpressing cancer was 21.4 +/- 14.3 mo vs 10.5 +/- 3.6 mo for those with overexpressing tumor. Among those not undergoing resection, the average survival for the 4 with nonoverexpressing cancer was 15.0 +/- 3.8 mo as contrasted to 5.2 +/- 2.1 mo for the overexpressors (p < 0.01). Although the number of patients is small, these findings suggest that the overexpression of HER2/neu gene product may be frequently found in pancreatic cancer of ductal origin and may be one of the useful prognostic biomarkers for this cancer.

Pancreatic cancer. Cytologic study of peritoneal washings

OBJECTIVE

To delineate the frequency and significance of free cancer cells in the peritoneal cavity of patients with pancreatic exocrine adenocarcinoma.

DESIGN

Randomly selected patients with pancreatic cancer had peritoneal washings performed at the beginning and conclusion of laparotomy. Results of cytologic studies were correlated with the clinical findings, size, spread, and resectability of the tumor and with the survival time of the patient. All patients were followed up until the present or until their deaths.

SETTING

Tertiary care, referral hospitals in Toledo, Ohio.

PATIENTS

Only patients with biopsy-proven adenocarcinoma of the pancreas were included. Thirty-six patients, yielding 62 specimens for cytologic study, were included.

INTERVENTION

Peritoneal washings were performed at the beginning and completion of laparotomy. Each washing was evaluated independently by two skilled cytologists. If present, ascites was quantitated and studied cytologically. Biopsy specimens were obtained in each patient at the time of the study.

MAIN OUTCOME MEASUREMENTS

Presence or absence of malignant cells in peritoneal fluid; maximal diameter, grade, and spread of cancer; presence and volume of ascitic fluid; resectability of cancer; and length of survival of the patient.

RESULT

Of the 36 patients studied, three had positive cytologic findings. All three had peritoneal carcinomatosis. Of 11 patients with ascites, only one had positive cytologic findings.

CONCLUSIONS

Results of cytologic studies of peritoneal washings or of ascitic fluid are seldom positive with pancreatic exocrine carcinoma. When positive, they denote a very grave prognosis.

Preferential pairing of T and B cells for production of antibodies without covalent association of T and B epitopes

T cell from H-2b mice recognize at least 12 sequence regions on the Torpedo acetylcholine receptor (TAChR) alpha, gamma and delta subunits. Immunization of C57BL/6 mice with individual synthetic TAChR sequences known to contain CD4+ epitopes resulted in most cases (10 out of 12 peptides) in anti-peptide antibody (Ab) production, indicating that short TAChR sequences contain both CD4+ and B epitopes. Immunization of C57BL/6 mice with a mixture of a CD4+ epitope peptide, from the TAChR or from an unrelated protein, plus another TAChR sequence forming a "pure" B epitope (T alpha 63-80), induced in most cases anti-peptide Ab and CD4+ cell sensitization only against the peptide containing the CD4+ epitope. However, when the T epitope peptide T alpha 360-378 was co-injected with the B epitope, Ab were also produced against the B epitope peptide. Injection of the individual peptides T alpha 360-378 and T alpha 63-80 at different and distant sites along the back of mice elicited sensitization of CD4+ cells and Ab production only against peptide T alpha 360-378. Therefore, when optimal cooperation between T and B cells occurs, spatial proximity but not covalent association of the B and the CD4+ epitope is necessary for production of Ab against the B epitope.

Characterization of the CGRP receptor and mechanisms of action in rat mesenteric small arteries

Rat alpha-calcitonin gene-related peptide-induced concentration-dependent (100 pM-10 nM) relaxations in rat mesenteric small arteries (i.d. approximately 220 microns) contracted with noradrenaline, prostaglandin F2 alpha or K+, however, the maximal relaxation depended on the precontractile stimulus, being highest (95%) in arteries contracted with PGF2 alpha and lowest (51%) in arteries contracted with 125 mM K+. The relaxation was inhibited between 10 pM and 1 nM by removal of the endothelium, but was not antagonized by glibenclamide (1 microM), tetraethylammonium (30 mM), apamine (0.3 microM) and 4-aminopyridine (3 mM). The concentration-response curve to rat alpha-CGRP and human beta-CGRP was shifted to the right in the presence of 1 microM human alpha-CGRP(8-37) indicating a receptor affinity, -log(KB[M]), equal to 7.2 and 7.0, respectively. It is concluded that the relaxation induced by CGRP depends minimally on the endothelium and K(+)-channel opening is not a principal process in the relaxing effect of CGRP, thus a third mechanism must mediate the relaxation in these vessels. The main CGRP receptor type mediating relaxation in rat mesenteric small arteries belongs to the CGRP1 subtype.

Intrahepatic biliary cystadenoma with intracystic gallstone formation

Biliary cystadenoma is a rare tumor of the liver. We describe a biliary cystadenoma of the left lobe of the liver with intracystic gallstone formation. This is the first report of stone formation in biliary cystadenoma of the liver.

Homologous kappa-neurotoxins exhibit residue-specific interactions with the alpha 3 subunit of the nicotinic acetylcholine receptor: a comparison of the structural requirements for kappa-bungarotoxin and kappa-flavitoxin binding

kappa-Flavotoxin (kappa-FTX), a snake neurotoxin that is a selective antagonist of certain neuronal nicotinic acetylcholine receptors (AChRs), has recently been isolated and characterized [Grant, G. A., Frazier, M. W., & Chiappinelli, V. A. (1988) Biochemistry 27, 1532-1537]. Like the related snake toxin kappa-bungarotoxin (kappa-BTX), kappa-FTX binds with high affinity to alpha 3 subtypes of neuronal AChRs, even though there are distinct sequence differences between the two toxins. To further characterize the sequence regions of the neuronal AChR alpha 3 subunit involved in formation of the binding site for this family of kappa-neurotoxins, we investigated kappa-FTX binding to overlapping synthetic peptides screening the alpha 3 subunit sequence. A sequence region forming a "prototope" for kappa-FTX was identified within residues alpha 3 (51-70), confirming the suggestions of previous studies on the binding of kappa-BTX to the alpha 3 subunit [McLane, K. E., Tang, F., & Conti-Tronconi, B. M. (1990) J. Biol. Chem. 265, 1537-1544] and alpha-bungarotoxin to the Torpedo AChR alpha subunit [Conti-Tronconi, B. M., Tang, F., Diethelm, B. M., Spencer, S. R., Reinhardt-Maelicke, S., & Maelicke, A. (1990) Biochemistry 29, 6221-6230] that this sequence region is involved in formation of a cholinergic site. Single residue substituted analogues, where each residue of the sequence alpha 3 (51-70) was sequentially replaced by a glycine, were used to identify the amino acid side chains involved in the interaction of this prototope with kappa-FTX.(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxing actions of corticotropin-releasing factor on rat resistance arteries

1. Although it well established that corticotropin-releasing factor (CRF) injected i.v. can cause hypotension and vasodilatation, there is no in vitro evidence that CRF acts as a vasodilator. We have therefore tested the hypothesis that the hypotensive effect of i.v. CRF is due to a direct vasodilator action by carrying out experiments in vitro on rat resistance arteries (i.d. 150-300 microns). 2. Initial in vivo experiments confirmed that CRF (1.5 nmol.kg-1) injected i.v. caused hypotension in rats, this being partially antagonized by the CRF analogue CRF9-41. 3. For the in vitro experiments, vessels were taken from the mesenteric, cerebral and femoral vascular beds, and mounted as ring preparations in an isometric myograph. The vessels were pre-contracted with one of 3 agonists (prostaglandin F2 alpha, arginine vasopressin or noradrenaline) or with a high-potassium solution (K+). 4. With maximal concentrations of the agonists, CRF caused relaxation of mesenteric and cerebral vessels with 10 nM, and near complete relaxation with 100 nM. Femoral vessels pre-constricted with agonists and all vessels pre-constricted with K+ were less affected by CRF. In the mesenteric vessels, with sub-maximal levels of pre-constriction, CRF caused substantial relaxation at 1 nM and could cause complete relaxation at 10 nM. 5. The relaxant effect of CRF on contractions of mesenteric vessels was antagonized by 100 nM CRF9-41. Neither tetraethyl ammonium (30 mM) nor glibenclamide (3 microM) antagonized the relaxant effect of CRF. 6. The relaxant effect of CRF on mesenteric small arteries was found to be unaffected by removal of the endothelium. 7. The results indicate that CRF causes an endothelial-independent vasodilatation of rat resistance arteries under in vitro conditions at concentrations which are consistent with this being an important cause of the hypotension observed with i.v. injection of CRF.

Monoclonal antibodies against synthetic sequences of the nicotinic receptor cross-react fully with the native receptor and reveal the transmembrane disposition of their epitopes

Monoclonal antibodies (mAbs) were derived from mice immunized with synthetic peptide sequence regions of the alpha subunit of the nicotinic acetylcholine receptor from Torpedo electric tissue (TAChR). Sequence-specific mAbs were obtained against the following peptides: alpha 1-20, alpha 291-308, alpha 304-322, alpha 332-350, alpha 346-364, alpha 360-378, alpha 376-393, alpha 390-409, and alpha 420-437. The ability of mAbs to recognize native TAChR was quantitated by immunoprecipitation of TAChR solubilized in the nondenaturing detergent Triton X-100. mAbs against peptide alpha 304-322, alpha 332-350, and alpha 360-378 cross-reacted with most or all Triton-solubilized TAChR molecules and, in immunoelectron microscopy experiments, bound to the cytoplasmic surface of AChR-rich postsynaptic membrane fragments. Two mAbs specific for the sequence alpha 376-393, proposed to form an amphypathic alpha helix possibly involved in formation of the ion channel, recognized only approximately 35% of Triton-solubilized TAChR molecules and did not react with membrane-bound TAChR. All of these sequence-specific antibodies recognized SDS-denatured TAChR alpha subunit in Western blots. MAbs specific for the amino-terminal sequence region of the alpha subunit, alpha 1-20, and for the sequences alpha 291-308, alpha 346-364, and alpha 390-409 did not recognize native TAChR. A mAb directed against the carboxyl-terminal region, alpha 420-437, recognized with low apparent titer Triton-solubilized TAChR, not membrane-bound TAChR. In conclusion, a complex membrane protein, TAChR, contains several continuous sequence segments exposed on the TAChR surface, because different mAbs raised against certain synthetic sequences recognized most or all native TAChR molecules. By analogy, it should be possible for most proteins of known sequence to raise anti-peptide antibodies fully cross-reactive with the native cognate protein.

Spinal interactions between opioid and noradrenergic agonists in mice: multiplicativity involves delta and alpha-2 receptors

The nature of the interaction between spinally administered opioid and alpha-2 agonists was investigated using the substance P behavioral test in mice. Morphine and agonists which more selectively activate mu or delta opioid receptors were co-administered intrathecally with direct and indirect acting adrenergic agonists norepinephrine, cocaine or clonidine and the behavioral responses to intrathecally coadministered substance P were evaluated. The ED50 values for agonists administered separately and concurrently were computed and drug interactions were evaluated using isobolographic analyses. After separate administration, all the opioid and adrenergic agonists inhibited the substance P-induced behavioral responses. Upon coadministration of opioid and adrenergic agonists, a multiplicative interaction was observed between morphine or the delta agonist D-Pen2-D-Pen-5-enkephalin and the adrenergic agonists. Additive or antagonistic interactions were found between the mu agonist Tyr-D-Ala-NMe-Phe-Gly(ol) and the same adrenergic agonists. The opioid antagonist naloxone and the alpha-2 adrenergic antagonist idazoxan were given as intrathecal pretreatments at doses chosen to shift the dose-response curves of their corresponding agonist (given alone) 4- to 10-fold to the right; this always resulted in a smaller, but significant (2- to 4-fold) shift in the dose-response curve of the other agonist given alone. Intrathecal pretreatment with naloxone or idazoxan altered some interactions between the opioids and clonidine. Although naloxone blocked completely the multiplicative interaction between morphine and clonidine, idazoxan did not. Both naloxone and idazoxan changed the antagonistic interaction between Tyr-D-Ala-NMe-Phe-Gly(ol) and clonidine to a multiplicative interaction. Neither antagonist blocked the multiplicative interaction between D-Pen2-D-Pen5-enkephalin and clonidine. These results suggest that: 1) interactions between opioid and adrenergic agonists in mouse spinal cord are mediated by delta and alpha-2 receptor subtypes; 2) the synergistic interaction between morphine and alpha-2 adrenergic agonists may involve action at delta opioid receptors; and 3) antagonist action on these drug interactions is complex.

Epitope mapping of monoclonal antibodies to Torpedo acetylcholine receptor gamma subunits, which specifically recognize the epsilon subunit of mammalian muscle acetylcholine receptor

Epitopes for four monoclonal antibodies (mAbs) to the gamma subunit of Torpedo nicotinic acetylcholine receptor (AChR), and one mAb crossreactive with the gamma and delta subunits of Torpedo AChR were mapped using overlapping synthetic peptides corresponding to the complete amino acid sequence of Torpedo gamma subunit. The epitopes for all mAbs were within a 50 residue sequence region, on the cytoplasmic surface of the AChR. Three mAbs crossreacted with mammalian muscle AChRs. Two of them specifically recognized the epsilon subunit of AChRs at adult neuromuscular junction. The epsilon-specific mAbs were used, in conjunction with mAbs specific for the alpha and beta subunits and anti-peptide antisera specific for the epsilon, gamma and delta subunits, to identify in Western blots the subunit complement of embryonic and adult bovine muscle AChRs.

T helper function of CD4+ cells specific for defined epitopes on the acetylcholine receptor in congenic mouse strains

We previously identified sequence segments of Torpedo acetylcholine receptor (TAChR) alpha subunit recognized by CD4+ cells of congenic mouse strains of different H-2 haplotypes, susceptible to experimental autoimmune myasthenia gravis. CD4+ cells from BALB/c and CB17 mice (H-2d) recognized the peptide sequences alpha 1-20 and alpha 304-322, while C57BL/6 and BALB/b mice (H-2b) recognized alpha 150-169 and alpha 360-378. C57BL/6 mice recognized to a lesser extent also peptide alpha 181-200. In the present study we demonstrate that CD4+ cells which recognize these epitopes have T-helper function. CD4+ cells from TAChR immunized mice, stimulated in vitro with synthetic epitope peptides, induced proliferation in vitro of B cells via soluble factors which were not strain specific, and induced secretion in vitro of anti-AChR antibodies. Upon in vitro stimulation with T-epitope peptides, they secreted interleukin-2. Immunization of mice with synthetic T-epitope peptides caused sensitization of CD4+ cells, which responded in vitro both to the immunizing peptides and to TAChR, and appearance of anti-AChR antibodies in vivo, further identifying the epitope-specific CD4+ cells as AChR-specific T-helper cells.

Experimental myasthenia gravis in congenic mice. Sequence mapping and H-2 restriction of T helper epitopes on the alpha subunits of Torpedo californica and murine acetylcholine receptors

Immunization of mice with nicotinic acetylcholine receptor from Torpedo electric organ (TAChR) causes a disease similar to human myasthenia gravis (experimental autoimmune myasthenia gravis, EAMG). Susceptibility to EAMG correlates with the H-2 haplotype. In this study we used overlapping synthetic peptide corresponding to the complete sequences of the alpha subunits from TAChR and murine muscle AChR (MAChR) to map T helper epitopes in congenic murine strains of different H-2 haplotype. C57BL/6 and BALB/B mice (highly susceptible to EAMG) and BALB/c and CB17 mice (less susceptible to EAMG), immunized with TAChR, developed similar anti-TAChR antibody titers and L3T4+ (T helper) cell sensitization. Different sequence segments of the TAChR alpha subunit were recognized by L3T4+ cells from strains of H-2b and H-2d haplotype. The sequence segments recognized by the H-2d strains have the highest predicted propensity to form amphipatic alpha helices, while those recognized by the H-2b strains do not. We investigated whether in EAMG T helper cells cross-react with autologous AChR sequences, and a true break of the tolerance occurs. Overlapping synthetic peptides, corresponding to the complete sequence of MAChR alpha subunit, were used to test L3T4+ cell from mice immunized with TAChR. L3T4+ cell strains did not cross-react with any murine peptide sequence, while L3T4+ cells from H-2d mice were strongly stimulated by the peptide sequence Ma alpha 304-322, which is very similar to the homologous Torpedo peptide.