# Glycolytic enzymes as autoantigens

Introduction

A lot of work has been done to attest the prevalence of glycolytic enzymes, and in particular of enolase, as autoantigens in autoimmune disorders. Antibodies to the isoform alpha (and to a lesser extent to the isoform gamma) of the enzyme enolase have been reported in a variety of immunological diseases (table 1), and yet the prevalence of these autoantibodies in ME/CFS has not been measured, so far, as has been recently pointed out (Sotzny F et al. 2018).

Anti-enolase Abs in ME/CFS

Recently a role for anti-gamma enolase Abs has been proposed in post-treatment Lyme disease syndrome: it has been postulated that sequence similitude between Borrelia own enolase and human enolase might be the cause of cross-reactive autoantibodies (Maccallini P et al. 2018).  A similar pathogenic role for anti-enolase antibodies has been previously proposed in PANDAS (Dale, et al., 2006) and in rheumatoid arthritis (Lee JY et al 2015), with the putative triggering bacterial enolases belonging to Streptococcus pyogenes and to Porphyromonas gingivalis, respectively. Besides molecular mimicry, a pathological increase in glycolytic enzymes expression has been proposed as the cause for the rise of autoantibodies to these proteins (Chang X et Wei Chao 2011). Both these triggering events are theoretically possible in ME/CFS, given that this disease is initiated by an infectious event in many cases (Hickie I et al. 2006) and an increase in glycolysis has been described in peripheral white blood cells from ME/CFS patients (Lawson N et al. 2016). Although autoimmunity against enolase is present in many autoimmune diseases, it seems that different autoepitopes are involved in different diseases (see epitopes in red, in table 2). So if we found autoantibodies to enolase in ME/CFS, we could perhaps find a specific autoepitope useful for diagnostic purposes.

Anti-enolase Abs and diseases

The first report of anti-enolase antibodies was in 1991. One woman with hyperthyroidism and vague muscular pain and another one with Raynaud’s phenomenon, both had serum reactive to all the three subunits of enolase (Rattner, et al., 1991). During the following years autoantibodies against enolase have been reported in systemic autoimmune diseases, such as Behçet’s disease (Lee, et al., 2003 ), rheumatoid arthritis (Saulot, et al., 2002), systemic lupus erythematosus, and systemic sclerosis (Pratesi, et al., 2000). They have been reported in organ specific autoimmune diseases too, such as cancer related retinopathy (Adamus, et al., 1996), autoimmune hepatitis, primary biliary cirrhosis (Akisawa, et al., 1997), hypophysitis (O’Dwyer, et al., 2002), discoid lupus erythematosus (Gitlits, et al., 1997), idiopathic juvenile arthritis, Crohn’s disease (Pontillo, et al., 2011); and in brain pathologies as Hashimoto’s encephalopathy (Fujii A1, et al., 2005), multiple sclerosis (Forooghian, et al., 2007), encephalitis lethargica (Dale, et al., 2004), PANDAS, Sydenham’s chorea (Dale, et al., 2006), and obsessive-compulsive disorder in adults (Nicholson, et al., 2012). Anti-enolase autoantibodies have been detected also in diseases of unknown etiology, such as Buerger’s disease and atherosclerosis (Witkowska, et al., 2005). Prevalence of anti-enolase antibodies in these diseases is reviewed in Table 1. P values are reported when available.

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