The thrombophilic network of autoantibodies in celiac disease

Celiac disease (CD) is the most common autoimmune food intolerance in the world. It is a life-long autoimmune condition [1] mainly of the gastrointestinal tract, affecting the small intestine of genetically susceptible individuals. Environmental factors are crucial for disease induction. Gluten, which is the storage protein of wheat and its alcohol-soluble gliadins are the offending inducers of the disease together with structurally related molecules found in barley, rye and oat. Tissue transglutaminase (tTG) is the autoantigen against which the abnormal immune response is directed [2] and two main autoantibodies, antiendomysium and anti-tTG, are currently the most useful serological markers to screen for the disease [3, 4]. The sequential chain of events operating in the disease was recently unraveled, and gives hope for future therapeutic strategies [5]. Furthermore, the epidemiology, prevalence and clinical presentation of CD are changing constantly and, with time, new clinical presentations are depicted that increase the clinical variability of CD [6].

It has been shown that the classical intestinal clinical picture of malnutrition, chronic diarrhea and nutritional deficiencies are disappearing and extraintestinal presentations are emerging. Skin, endocrine, skeletal, hepatic, hematological, gynecological, fertility, dental and behavioral abnormalities are often described [7‐9]. Nowadays, we are witnessing an epidemiological shift in the disease phenotype toward a more advanced age, and increased prevalence of latent, hyposymptomatic or asymptomatic presentations [6].

A newly explored area of CD is hypercoagulability and the resulting thromboembolic phenomena. There is an increase risk of stroke in adults and children with CD [10‐15]. Thrombophilia, pregnancy loss, deep vein thrombosis, small bowel infarction, atrial fibrillation, Budd-Chiari syndrome, portal and splenic vein thrombosis, and cardiovascular disease have been described [16‐21]. Even the onset of the disease may be due to a thrombotic event [11, 17, 21]. Hyperhomocysteinemia with related vitamin deficiency in untreated CD, the frequency of methylenetetrahydrofolate reductase variants and the high homology between factor XIII and tTG add to the hypercoagulable status in patients [21‐26].

In fact, there is an increased incidence of autoimmune diseases in CD [1, 7, 27, 28]. Two examples associated with thrombophilia are systemic lupus erythematosus (SLE) and antiphospholipid (aPL) syndrome [29, 30]. Three autoantibodies associated with the two entities are antiphosphatidylserine/prothrombin (aPS/PT), aPL and antiprothrombin (aPT). aPS/PT and aPL autoantibodies confer increased risk for thromboembolic events and poor outcome in those diseases [31‐39]. The correlation between aPS/PT antibodies and clinical manifestations of aPL syndrome and the importance of aPS/PT as a marker for this syndrome are well established. The relationship between aPS/PT antibodies and hypercoagulability state is further strengthened by their increased incidence in cerebral infarction [40]. aPT autoantibodies are prevalent in SLE and aPL syndrome and are associated with thrombosis and pregnancy morbidity [41‐44].

Despite the coexistence of CD and thromboembolic events, the aPS/PT and aPT status has never been investigated and aPL activity has scarcely been investigated in CD. On the above backgrounds of aPS/PT, aPT and aPL antibodies and thrombophilia, hypercoagulability in CD, and increased incidence of SLE and aPL in CD, the presence of aPS/PT, compared with aPL, aPT and anticardiolipin antibodies, were explored in children with CD and their parents, compared with pediatric controls. Increased incidence of aPS/PT IgG in the celiac group and intermediate incidence in their parents, compared with none in the control group, was detected. Additionally, higher rates of activities of aPS/PT IgM and prothrombin IgG autoantibodies in the celiac patients compared with the other two groups were detected. It seems that the presently studied thrombophilic autoantibodies are operative in CD, extending the hypercoagulability network in this disease.

No epidemiological statistical difference between the pediatric groups (groups 1 and 2) was detected. None of the participants were IgA deficient and all were screened also by IgG-tTG antibodies. None of the parents (group 3) at the time of the study had positive serology for CD, despite consuming gluten. No correlation was found between parents and children concerning the results.

Table 1 shows the mean ±SD and median of the different autoantibodies in group 1 (pediatric CD), group 2 (pediatric control) and the parents of group 1. Table 2 shows the mean of percentage positivity of the optical density of the autoantibodies in group 1 (pediatric CD) and group 3 (parents) compared with the healthy controls, group 2.

The main result of the present study is the increased incidence of aPS/PT IgG in the celiac group and intermediate incidence in their parents, compared with none in the control group. Secondary results are the increased rates of aPS/PT IgM and prothrombin IgG autoantibodies in the celiac patients compared with the other two groups. Of note is the constant, parallel, gradual decrease of the levels of aPS/PT IgG and IgM across the continuum of the three groups, from celiac children, to their parents, to pediatric controls. The fact that none of the parents had positive celiac serology points to a potential genetic influence on the presence of aPS/PT autoantibodies. In fact, being an autoimmune disease with a well-established genetic susceptibility and increased familial predisposition, the increased presence of autoantibodies and autoimmune diseases in first-degree relatives of CD patients is well known [47‐49] and aPS/PT should be added to the list. Additionally, aPS/PT should be added to the increasing list of autoantibodies associated with CD-affected patients [27, 28].

Despite the fact that many of the autoantibodies might present an epiphenomenon, it is suggested that mainly aPS/PT, but also antithrombin and aPL autoantibodies, are pathogenic and play an active role in CD pathogenesis and complications. The presence of aPS/PT is directly related to thromboembolic events in aPL syndrome, SLE and cerebral infarction [31‐40]. The thrombogenic properties of aPS/PT correlate with increased thrombin generation in aPL syndrome, contributing to the understanding of the pathophysiology of thrombophilia in these patients [36]. Those autoantibodies are strong risk factors for venous thromboembolism in patients with SLE because they induce activated protein C resistance [37]. The other two IgG autoantibodies, namely antithrombin and aPL, are also associated with thrombotic events in aPL syndrome and SLE [32, 33, 50, 51], and are risk factors for myocardial infarction in middle-aged men [52, 53].

The pathophysiology of the thromboembolic phenomena associated with CD [10‐26] represents a puzzle with multiple constituents: hyperhomocysteinemia; B12 and\or folate deficiency; methylenetetrahydrofolate reductase mutations; the high homology between blood coagulation factor XIII and tTG; and protein C and S deficiency due to vitamin K deficiency [21‐26, 54]. The present study unravels a series of autoantibodies, aPL, aPT and mainly aPS/PT, that form part of this puzzle and are suggested to play a pathogenic role in the thrombogenicity of CD.

Phosphatidylserine is a regular constituent of the inner leaflet of the cell membrane, which is only exposed on the outside of the cell membrane during apoptosis or because of damaged endothelial cells [55]. It is known that prothrombin and aPL antibodies bind specifically to the surface of apoptotic cells [56, 57]. Recently, Ieko et al.[58] reported that aPS/PT IgG recognizes prothrombin bound to phosphatidylserine on platelets and endothelial cells and, directly or via Fc-gamma receptors, activates a variety of procoagulant agents. However, the complementary aspects of CD are endothelial dysfunction [59], platelet abnormalities [60, 61] and increased apoptosis [62]. Thus, it is suggested that intestinal injury, endothelial dysfunction, platelet abnormalities and enhanced apoptosis cause increased exposure of phospholipids or new epitopes, which are the origin of aPT, aPL and aPS/PT autoantibodies. Those antibodies might play a pathogenic role in the thrombophilia associated with CD.

New light was recently shed on the ‘inflammation coagulation crosstalks’ [63]. Recent studies have unveiled molecular underpinnings of the intimate interconnection between both systems. Being a classical inflammatory state, CD can present such crosstalks, resulting in enhanced coagulability in the intestinal arena and on the systemic level. Because there are several pathways of mucosal injury, autoantigens like phospholipids, phosphatidylserine and prothrombin are exposed, inducing the production of aPS/PT, aPL and aPT antibodies. With their thrombogenic capacities, those autoantibodies can present the first or an additional hit in the thrombogenic background operating in CD. Because of the increased coagulability in CD and the harmful potential consequences, patients positive for those antibodies should be considered to receive preventive anticoagulant therapy.

We detected increased incidence of aPS/PT IgG in the pediatric celiac group and intermediate incidence in their parents, compared with no incidence in the control group. Additionally, higher rates of activity for aPS/PT IgM and prothrombin IgG autoantibodies were observed in the patients with CD compared with the other two groups. Based on the extensive literature of thromboembolic phenomenon described in CD, it seems that the thrombophilic autoantibodies studied here are operative in CD, extending the hypercoagulability network of the disease. The use of the autoantibodies described in this study as potential markers for thromboembolic manifestations in CD is a subject for future exploration.