Human monoclonal immunoglobulins that bind the human acetylcholine receptor

The potential role of cell surface complement regulators and circulating CD4+ CD25+ T-cells in the development of autoimmune myasthenia gravis

INTRODUCTION

CD4+CD25+ regulatory T-lymphocytes (T-regs) and regulators of complement activity (RCA) involving CD55 and CD59 play an important role in the prevention of autoimmune diseases. However, their role in the pathogenesis of human autoimmune myasthenia gravis (MG) remains unclear. This study aimed to determine the frequency of peripheral blood T-regs and CD4+ T-helper (T-helper) cells and the red blood cells (RBCs) level of expression of CD55 and CD59 in MG patients.

METHODS

Fourteen patients with MG in neurology outpatient clinics of Sohag University Hospital and Sohag General Hospital from March 2014 to December 2014, and 10 age-matched healthy controls participated in this case-control study. We did flowcytometric assessments of the percentage of peripheral T-regs and T-helper cells and the level of expression of CD55 and CD59 on RBCs in the peripheral blood of patients and controls.

RESULTS

There was a statistically significant decrease in the percentage of peripheral blood T-regs and T-regs/T-helper cell ratio in the MG patients group. Moreover, the level of expression of CD55, CD59, and dual expression of CD55/CD59 on RBCs were statistically significantly lower in MG patients than those of healthy controls. However, regression analysis indicated that there was no significant correlation between all the measured parameters and disease duration or staging.

CONCLUSION

Functional defects in the T-regs and RCA may play a role in the pathogenesis of autoimmune MG and their functional modulation may represent an alternative therapeutic strategy for MG treatment.

Myasthenia gravis: past, present, and future

Myasthenia gravis (MG) is an autoimmune syndrome caused by the failure of neuromuscular transmission, which results from the binding of autoantibodies to proteins involved in signaling at the neuromuscular junction (NMJ). These proteins include the nicotinic AChR or, less frequently, a muscle-specific tyrosine kinase (MuSK) involved in AChR clustering. Much is known about the mechanisms that maintain self tolerance and modulate anti-AChR Ab synthesis, AChR clustering, and AChR function as well as those that cause neuromuscular transmission failure upon Ab binding. This insight has led to the development of improved diagnostic methods and to the design of specific immunosuppressive or immunomodulatory treatments.

Immunological specificity and cross-reactivity of anti-acetylcholine receptor and anti-presynaptic membrane receptor antibodies in myasthenia gravis

Antibodies against acetylcholine receptor (AChR), a protein that binds to alpha-bungarotoxin (alpha-BuTx), are characteristic for myasthenia gravis (MG) and are considered to be of importance in the pathogenesis of the disease. Antibodies against a beta-BuTx binding protein, presynaptic membrane receptor (PsmR), have also been reported in most MG patients. We have analysed the specificity and cross-reactivity of antibodies to bovine AChR and PsmR in sera from 11 patients with MG. More than 90% of antibodies to PsmR were adsorbed specifically by PsmR conjugated affinity chromatography. Similarly, more than 90% of anti-AChR antibodies were absorbed by AChR conjugated affinity chromatography. Specificities of antibodies from affinity chromatography were also confirmed by ELISA and agarose isoelectric focusing. However, the antibodies to PsmR and AChR from MG patients' sera showed about 45-55% cross-reactivity, and there was a high correlation between serum levels of both antibodies. The demonstration of anti-PsmR antibodies could be important in documenting presynaptic damage and understanding the pathogenetic process in MG.

Acetylcholine receptor-reactive T and B cells in myasthenia gravis and controls

Myasthenia gravis (MG) is strongly associated with antibodies to acetylcholine receptor (AChR), whereas the extent of T cell involvement is not settled. The number of cells secreting interferon-gamma (IFN-gamma) in response to AChR during 48 h culture of blood mononuclear cells (PBL) may reflect AChR-reactive T cells. Using an immunospot assay, we detected such cells in 23 of 30 patients with MG at a mean number of 1 per 33.333 PBL. AChR-reactive T cells were also found in patients with other neurological diseases (OND) and in healthy subjects but at lower frequencies and numbers. The T cell response to purified protein derivative and to PHA, and also to two major myelin proteins (basic protein and proteolipid protein) did not differ between MG and the two control groups, underlining the specificity of an augmented T cell reactivity to AChR in MG. Evaluation of the B cell response by enumerating anti-AChR IgG antibody secreting cells revealed such cells in 27 of 28 patients with MG at a mean value of 1 per 14,085 PBL. Cells secreting anti-AChR antibodies of the IgA and IgM isotypes were also detected in MG, but less frequently, at lower numbers, and only in conjunction with IgG antibody secreting cells. Anti-AChR antibody secreting cells were also found among patient with OND and in healthy controls, but at lower frequencies and numbers. These data confirm that AChR is a major target for autoimmune response in MG.

Anti-presynaptic membrane receptor antibodies in myasthenia gravis

Myasthenia gravis (MG) is considered as an autoimmune disease of neuromuscular junction resulting from antibodies directed to acetylcholine receptors (AChR). We describe the use of beta-bungarotoxin (beta-BuTx) and alpha-bungarotoxin (alpha-BuTx) to capture their corresponding proteins from preparation of crude human muscle receptor. beta-BuTx binds to presynaptic membrane receptor (PsmR) of the whole receptor fraction, while alpha-BuTx binds to AchR. The captured proteins were used as antigen in ELISA to detect antibodies to PsmR and to AchR in sera from 82 Chinese patients with MG and in controls. In MG, antibodies to PsmR only were detected in 13%, to AchR only in 11% and both to PsmR and AchR in 54%. Only 3 of 50 patients with other neurological diseases and none of 50 healthy subjects had these antibodies. Specificity tests for antibodies showed that the detection systems which we used are specific and confident. No correlation was found between antibody levels and clinical status. The significance of the PsmR antibodies in the pathogenesis of MG is unknown. We suggest that myasthenia gravis is not only due to damage of the postsynaptic membrane, but of presynaptic structures as well.

Cytokine regulation of HLA on thyroid epithelial cells

The regulation of class I and class II HLA expression in human thyroid follicular cells was studied in vitro. Tumour necrosis factor-alpha (TNF-alpha) enhanced the expression of class I antigen on thyrocytes, but these cytokines had little effect on the expression of class II antigen. Interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) did not affect class I and class II antigen expression. The combination of interferon-gamma (IFN-gamma) with TNF-alpha or IL-1 beta enhanced the induction of class I and class II antigens, compared with the effect of IFN-gamma alone. Neither class I nor class II expression was induced by IL-6 alone or in combination with IFN-gamma. These findings suggest that TNF-alpha and IL-1 beta may have an important role in inappropriate expression of HLA antigens on thyrocytes in thyroid gland.

Acetylcholine receptor antibodies in primary biliary cirrhosis: characterization of antigen and idiotypic specificity

Auto-antibodies against the acetylcholine receptor of skeletal muscle are considered to be the cause of the neuromuscular dysfunction in myasthenia gravis. However, such auto-antibodies also occur in disease states not accompanied by neuromuscular symptoms. Patients with primary biliary cirrhosis have a high prevalence of different auto-antibodies, including antibodies against the acetylcholine receptor. In primary biliary cirrhosis, these anti-receptor antibodies are predominantly of IgM isotype. The IgM antibodies show a broader reactivity with receptors from other species than antibodies from myasthenic patients. Immunoglobulins from patients with primary biliary cirrhosis bear the same receptor antibody-associated idiotypes, but the repertoire is quantitatively different from that found in myasthenia gravis patients. The IgM receptor antibody activity in a serum from a patient with primary biliary cirrhosis could be inhibited by cardiolipin, poly[dT], poly[I], and ssDNA, whereas this antibody activity in serum from a patient with myasthenia gravis was slightly reduced only by cardiolipin. Generally, IgM antibodies from patients with primary biliary cirrhosis had a broader reactivity with polynucleotides and phospholipids than IgG antibodies and antibodies from patients with myasthenia gravis. These results indicate a difference in the fine specificity between acetylcholine receptor antibodies in primary biliary cirrhosis and in myasthenia gravis.

B cell and autoantibody repertoire in a pair of monozygotic twins discordant for myasthenia gravis

A pair of identical twins, 47 years of age, who have been discordant for myasthenia gravis for 15 years were studied with regard to clinical status, neuromuscular function, and presence and properties of myasthenia specific autoantibodies. The autoantibody repertoire was tested in serum, as produced by peripheral lymphocytes in culture and as revealed by B cell lines. The healthy twin had no clinical signs of myasthenia and no signs of impaired neuromuscular function on electrophysiological tests. The autoantibody repertoire and the avidity of the anti-receptor antibodies were similar in both individuals. Epstein-Barr virus transformation of peripheral lymphocytes revealed a higher incidence of B cells committed to make autoantibodies in the healthy twin than in her myasthenic sister.

Anti-idiotypic B-cell lines from a patient with monoclonal gammopathy of undetermined significance

The B-cell repertoire in a patient with benign monoclonal gammopathy of unknown significance was studied using Epstein-Barr virus transformation of peripheral lymphocytes. The presence of anti-idiotypic B cells producing monoclonal antibodies that reacted with idiotypic determinants on the monoclonal immunoglobulin was verified. The two monoclonal anti-idiotypic antibodies studied were of the IgM-kappa type. Such anti-idiotypic antibodies may be part of an idiotypic network regulation of the monoclonal B-cell population.