Spontaneous production of anti-IFN-  and anti-IL-12 autoantibodies by thymoma cells from myasthenia gravis patients suggests autoimmunization in the tumor

Abstract

Myasthenia gravis (MG) is mediated by autoantibodies to the acetylcholine receptor (AChR), expressed in muscle and rare thymic myoid cells. Most early-onset cases show thymic lymph node-type infiltrates, including pre-activated plasma cells spontaneously producing anti-AChR antibodies. Since these are not evident in the associated thymomas found in another 10% of MG patients, AChR-specific B cells must be autosensitized elsewhere. Unexpectedly, at diagnosis, >70% of MG/thymoma patients also have high-titer neutralizing autoantibodies to IFN-alpha, and >50% to IL-12; moreover, titers increase strikingly if the thymomas recur, indicating a closer tumor relationship than for anti-AChR. To investigate this, we have measured autoantibody production by cells cultured from thymomas, any available thymic remnants and blood, with or without the B cell stimulant pokeweed mitogen (PWM). To check autoantibody specificity and clonal origins, we isolated Fabs from two combinatorial libraries from producer thymus/thymoma cells. Surprisingly, thymoma cells spontaneously produced antibodies to IFN-alpha and/or IL-12 in >40% of seropositive cases, showing typical plasma cell behavior, whereas they produced anti-AChR only after PWM stimulation. We isolated 15 combinatorial Fabs to IFN-alpha (versus only one to AChR). Their strong binding in radio-immunoprecipitation and Western blots implies high affinities. The four Fabs tested neutralized anti-viral actions of IFN-alpha. The diverse V genes clearly showed ongoing antigen-driven selection. These results imply pre-activation in situ by native IFN-alpha/IL-12 expressed within a 'dangerous' tumor microenvironment. With these molecules, it should be easier to identify provoking cell type(s) that may give novel additional clues to autoimmunization against T-cell epitopes from the more complex AChR.

Biological implications of thymectomy for myasthenia gravis

“…25,26 The precise role of these autoantibodies to specifi c cytokines is unclear; however, a function to modify Th1/Th2 balance or stimulate some T-cell subsets, resulting in the onset of autoimmunity, is possible. On the other hand, this notion does not explain the high incidence of the association of MG with thymoma.…”

Radioligand-Binding Assay Reveals Distinct Autoantibody Preferences for Type I Interferons in APS I and Myasthenia Gravis Subgroups

“…We have hypothesized additional active autoimmunization there to explain the focus on ectodermal and endocrine targets in APS I and/or on muscle autoantigens in thymoma patients, and on type I IFNs in both [23,24]. That is supported by the increased levels of IFNs and IL-12 autoAbs when thymomas recur [21], and by their spontaneous production of these autoAbs by thymoma cells in culture [15].…”

“…Interestingly, many patients with the neuromuscular autoimmune disorder myasthenia gravis (MG) also have autoAbs against type I IFNs, especially the~10% with thymoma-associated/paraneoplastic MG [14][15][16]. Antibodies against Th17-related cytokines are largely restricted to rare cases with CMC [9].…”

Characterization of the immunoreactivity of anti-interferon alpha antibodies in myasthenia gravis patients. Epitope mapping

“…The appearance of auto-antibodies to IFN a in autoimmune disease could be related to an ongoing IFN a production by dendritic cells [23,24] and likely related to an auto-immunizing process mediated by these cells probably from a thymic environment [25,26]. The induction of IFN g by IFN a or by some infectious agent might be the basis of this auto-immunizing process.…”