Rhabdomyosarcoma cell line can be used for the isolation of soluble acetylcholine receptor and for assaying blocking and modulating autoantibodies

Novel complement inhibitor limits severity of experimentally myasthenia gravis

OBJECTIVE

Complement mediated injury of the neuromuscular junction is considered a primary disease mechanism in human myasthenia gravis and animal models of experimentally acquired myasthenia gravis (EAMG). We utilized active and passive models of EAMG to investigate the efficacy of a novel C5 complement inhibitor rEV576, recombinantly produced protein derived from tick saliva, in moderating disease severity.

METHODS

Standardized disease severity assessment, serum complement hemolytic activity, serum cytotoxicity, acetylcholine receptor (AChR) antibody concentration, IgG subclassification, and C9 deposition at the neuromuscular junction were used to assess the effect of complement inhibition on EAMG induced by administration of AChR antibody or immunization with purified AChR.

RESULTS

Administration of rEV576 in passive transfer EAMG limited disease severity as evidenced by 100% survival rate and a low disease severity score. In active EAMG, rats with severe and mild EAMG were protected from worsening of disease and had limited weight loss. Serum complement activity (CH(50)) in severe and mild EAMG was reduced to undetectable levels during treatment, and C9 deposition at the neuromuscular junction was reduced. Treatment with rEV576 resulted in reduction of toxicity of serum from severe and mild EAMG rats. Levels of total AChR IgG, and IgG(2a) antibodies were similar, but unexpectedly, the concentration of complement fixing IgG(1) antibodies was lower in a group of rEV576-treated animals, suggesting an effect of rEV576 on cellular immunity.

INTERPRETATION

Inhibition of complement significantly reduced weakness in two models of EAMG. C5 inhibition could prove to be of significant therapeutic value in human myasthenia gravis.

Frequency of anti-AChR epsilon subunit-specific antibodies in MG

A definite diagnosis of myasthenia gravis (MG) relies heavily on acetylcholine receptor (AChR) antibody testing. The relatively high number of antibody-negative patients therefore, causes frequent uncertainty in confirming the diagnosis. We evaluated the sensitivity and specificity of a new, commercially available AChR antibody test that uses an approximately equal mixture of AChR from TE671-epsilon (adult type) and TE671-gamma (fetal type) cells. This assay was used to re-examine 365 seronegative MG sera in which AChR antibody had not been detected by the standard assay that uses fetal type AChR. The new assay detected anti-AChR antibodies in 17 (15.5%) of 110 patients with ocular type and in 33 (12.9%) of 255 patients with generalized type MG. Anti-AChR epsilon subunit-specific antibodies were present in 13.7% of the patients in whom no AChR antibody had been detected by the standard assay, showing an increase from 79 to 82% in overall diagnostic sensitivity.

Identification of a peptide that protects the human acetylcholine receptor against antigenic modulation

mAb 192 is a rat monoclonal antibody with very high affinity for the major immunogenic region (MIR) of the human muscle acetylcholine receptor (AChR). An epitope mimic of this antibody was selected from a phage display peptide library screened with mAb 192. The peptide-presenting phage has been shown to specifically bind to solid phase mAb 192 with an equilibrium dissociation constant (K(d)) of 8.45x10(-9) M, as directly measured with surface plasmon resonance. This value represents the avidity of the interaction between selected phage and mAb 192. A synthetic version of this peptide QPSPYNGWRMEI, referred to as MG15, binds to its selecting antibody and blocks the interaction of mAb 192 with human AChR. Peptide MG15 was able to protect acetylcholine receptors on human RD cells from antibody-mediated down-modulation. The negative charge of glutamic acid plays a important role in antibody binding. Replacement of the glutamic acid with an alanine completely abolishes the inhibitory activity.

Measurement of c-erbB-2 proteins in sera from patients with carcinomas and in breast tumor tissue cytosols: correlation with serum tumor markers and membrane-bound oncoprotein

Using a commercial kit with antibodies against the ectodomain of c-erbB-2 protein, we detected c-erbB-2 immunoreactivity in human serum. We found that the percentages of patients with elevated serum c-erbB-2 immunoreactivities were 35, 21, and 9% in breast, prostate, and ovarian carcinoma, respectively. The majority of the elevated immunoreactivities were associated with sera containing highly elevated tumor markers with the highest in breast carcinoma (35%) and lowest in ovarian cancer (9%). Excellent correlations were also observed between the serum levels of c-erbB-2 immunoreactivity and the dominant tumor markers in serial specimens from individual cancer patients. We could also detect the c-erbB-2 immunoreactivity in the cytosols prepared from the breast tumor tissue for estrogen and progesterone receptor (ER & PgR) measurements using the same commercial kit for serum studies, and the intact c-erbB-2 oncoprotein (p185) in the extracts of the tissue membrane fractions with a different kit designed for tissue extract. The level of c-erbB-2 immunoreactivity in the cytosol from 124 human breast tumor specimens had an excellent correlation with the cell membrane concentrations of p185 (gamma = 0.89). Most of the elevated cytosol c-erbB-2 immunoreactivities were also found to associate with breast tumor specimens containing low concentrations of ER & PgR. It appears that measuring the c-erbB-2 immunoreactivity potentially could be used as a prognostic marker without performing tissue biopsies and also as a serum tumor marker for managing cancer patients.

Purification of PSA-ACT complex: characterization of PSA-ACT complex by various chromatographic procedures

We have explored various chromatographic procedures with the intention of establishing an isolation procedure that would allow us to isolate a large quantity of PSA-ACT (prostate specific antigen-alpha 1-antichymotrypsin) complex either from patients' sera or from incubation mixtures of free PSA and protease inhibitors. We found that at pH 7.2, both free PSA and PSA-ACT molecules are negatively charged and bind to the DEAE-Sepharose column. However, they could be separated from each other using a linear gradient of NaCl at pH 7.2. Both free PSA and PSA-ACT molecules were also found to be retained by the Con A Sepharose column because of the carbohydrate moiety of the PSA molecule. These two molecules were not separable by Con A chromatography. These two molecules apparently differ in their isoelectric points and were well separated by chromatofocusing using a pH gradient from pH 9 to 6. It appears that chromatofocusing can also be used to identify the isoforms of free PSA because of its high resolving power. The large difference in molecular size between free PSA and PSA-ACT complex allowed their separation by gel filtration chromatography on a column containing either S-100, S-200, or S-300 gel. S-200 gel appeared to be the best for the separation of free PSA from PSA-ACT and for the removal of other contaminating serum proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of free PSA isoforms, PSA complex formation, and specificity of anti-PSA antibodies by HPLC and PAGE-immunoblotting techniques

Both high performance liquid chromatographic (HPLC) and polyacrylamide gel electrophoresis-immunoblotting (PAGE-immunoblotting) procedures have been established for the study of isoforms of free prostate-specific antigen (PSA) and the complex formation between free PSA and protease inhibitors, and for the evaluation of the specificities of various anti-PSA antibodies. We found multiple isoforms of free PSA on PAGE, which were all capable of forming complexes with protease inhibitors. The same isoform pattern can be produced from the original seminal fluid. The PSA isoforms differ from each other most likely in charge because they could be converted to one band on SDS-PAGE and to a single peak by gel filtration chromatography. We found it difficult to form large quantities of PSA complex when mixing free PSA from seminal fluid with protease inhibitors, regardless of whether the free PSA or the protease inhibitors were in excess. Except for the PSA-ACT complex, which was consistently detectable by both HPLC and PAGE-immunoblotting techniques after incubation, these two procedures disagreed in their detection of PSA-A2M and PSA-AT complexes. The PSA-A2M complex was usually observable by immunoblotting techniques but barely detectable on HPLC, whereas PSA-AT was totally invisible by immunoblotting but appeared as a peak in the HPLC elution profile. Mixing free PSA with serum clearly resulted in both PSA-ACT and PSA-A2M complexes. However, more PSA-ACT than PSA-A2M was formed; the result was also confirmed by using 125I-PSA for mixing. PSA could be separated into active and inactive PSA by DEAE Sepharose chromatography with a 14-fold difference in protease activity. The difference in enzymatic activity apparently had no effect on complex formation. All the anti-PSA antibodies examined in this study reacted with PSA isoforms, PSA-ACT and PSA-A2M complexes. We conclude that it would be almost impossible to establish an assay to measure all forms of PSA in the serum and to expect to produce precise and accurate PSA values.