Anti-Yo Antibody Uptake and Interaction with Its Intracellular Target Antigen Causes Purkinje Cell Death in Rat Cerebellar Slice Cultures: A Possible Mechanism for Paraneoplastic Cerebellar Degeneration in Humans with Gynecological or Breast Cancers

Abstract

Anti-Yo antibodies are immunoglobulin G (IgG) autoantibodies reactive with a 62 kDa Purkinje cell cytoplasmic protein. These antibodies are closely associated with paraneoplastic cerebellar degeneration in the setting of gynecological and breast malignancies. We have previously demonstrated that incubation of rat cerebellar slice cultures with patient sera and cerebrospinal fluid containing anti-Yo antibodies resulted in Purkinje cell death. The present study addressed three fundamental questions regarding the role of anti-Yo antibodies in disease pathogenesis: 1) Whether the Purkinje cell cytotoxicity required binding of anti-Yo antibody to its intraneuronal 62 kDa target antigen; 2) whether Purkinje cell death might be initiated by antibody-dependent cellular cytotoxicity rather than intracellular antibody binding; and 3) whether Purkinje cell death might simply be a more general result of intracellular antibody accumulation, rather than of specific antibody-antigen interaction. In our study, incubation of rat cerebellar slice cultures with anti-Yo IgG resulted in intracellular antibody binding, and cell death. Infiltration of the Purkinje cell layer by cells of macrophage/microglia lineage was not observed until extensive cell death was already present. Adsorption of anti-Yo IgG with its 62 kDa target antigen abolished both antibody accumulation and cytotoxicity. Antibodies to other intracellular Purkinje cell proteins were also taken up by Purkinje cells and accumulated intracellularly; these included calbindin, calmodulin, PCP-2, and patient anti-Purkinje cell antibodies not reactive with the 62 kDa Yo antigen. However, intracellular accumulation of these antibodies did not affect Purkinje cell viability. The present study is the first to demonstrate that anti-Yo antibodies cause Purkinje cell death by binding to the intracellular 62 kDa Yo antigen. Anti-Yo antibody cytotoxicity did not involve other antibodies or factors present in patient serum and was not initiated by brain mononuclear cells. Purkinje cell death was not simply due to intraneuronal antibody accumulation.

The Role of Pathogenic Autoantibodies in Autoimmunity

“…Fc-mediated internalization of autoantibodies may be of particular significance in the brain, where Fc receptors are widely distributed in neural tissue, increase during aging, and may be involved in neurological disorders [91,190]. Fc-dependent uptake of IgG has been shown by neurons, particularly Purkinje cells, with accumulation in the cytoplasm and microtubular transport within the cell [90,[191][192][193][194][195].…”

“…It has been assumed that pathogenesis is primarily T-cell mediated in the autoimmune diseases in which they occur, and the autoantibodies are merely markers of an autoimmune response. In this context, a recent study of uptake of autoantibodies to the cytoplasmic autoantigen Yo in Purkinje cells is of particular interest [193]. Anti-Yo is associated with paraneoplastic cerebellar degeneration associated with gynaecological and breast malignancies and is representative of a larger group of autoantibodies in paraneoplastic neurological syndromes targeting intracellular proteins [170].…”

“…The role of these autoantibodies has been unclear, as autoantibody levels do not correlate with disease severity, and prognosis is poor despite immunotherapies [202]. However, anti-Yo was shown to penetrate Purkinje cells, accumulate intracellularly, bind to the Yo antigen, and cause cell death, providing direct evidence that the autoantibodies may be directly pathogenic [193].…”

“…SPS has been successfully treated with intravenous Ig, and is the treatment of choice for intractable SPS [234,235], suggesting that antibodies may be important in pathogenesis. Although both GAD65 and GAD67 are intracellular antigens, the mAbs b78 and b96.11 have been shown to penetrate the AF5 rat CNS cell line [228], possibly being internalised by Fc receptors that are widely distributed in neural tissue including Purkinje cells [192,193]. As Purkinje cells are the major source of GABA in the brain, uptake of anti-GAD could disrupt function in these cells.…”

Debate on the pathogenesis of paraneoplastic cerebellar degeneration with anti‐Yo antibody: T‐cell mediated or antibody mediated?

“…Recently, Greenlee et al . reported a pathogenic role of anti‐Yo antibody in Purkinje cell death with serum immunoglobulin G (IgG) from patients with PCD.…”