[Thymus function and autoimmunity]

[Thymoma and autoimmune diseases]

The association between thymoma and autoimmunity is well known. Besides myasthenia gravis, which is found in 15 to 20% of patients with thymoma, other autoimmune diseases have been reported: erythroblastopenia, systemic lupus erythematosus, inflammatory myopathies, thyroid disorders, Isaac's syndrome or Good's syndrome. More anecdotally, Morvan's syndrome, limbic encephalitis, other autoimmune cytopenias, autoimmune hepatitis, and bullous skin diseases (pemphigus, lichen) have been reported. Autoimmune diseases occur most often before thymectomy, but they can be discovered at the time of surgery or later. Two situations require the systematic investigation of a thymoma: the occurrence of myasthenia gravis or autoimmune erythroblastopenia. Nevertheless, the late onset of systemic lupus erythematosus or the association of several autoimmune manifestations should lead to look for a thymoma. Neither the characteristics of the patients nor the pathological data can predict the occurrence of an autoimmune disease after thymectomy. Thus, thymectomy usefulness in the course of the autoimmune disease, except myasthenia gravis, has not been demonstrated. This seems to indicate the preponderant role of self-reactive T lymphocytes distributed in the peripheral immune system prior to surgery. Given the high infectious morbidity in patients with thymoma, immunoglobulin replacement therapy should be considered in patients with hypogammaglobulinemia who receive immunosuppressive therapy, even in the absence of prior infection.

Immunology in the clinic review series: focus on type 1 diabetes and viruses: the role of viruses in type 1 diabetes: a difficult dilemma

Convincing evidence now indicates that viruses are associated with type 1 diabetes (T1D) development and progression. Human enteroviruses (HEV) have emerged as prime suspects, based on detection frequencies around clinical onset in patients and their ability to rapidly hyperglycaemia trigger in the non-obese diabetic (NOD) mouse. Whether or not HEV can truly cause islet autoimmunity or, rather, act by accelerating ongoing insulitis remains a matter of debate. In view of the disease's globally rising incidence it is hypothesized that improved hygiene standards may reduce the immune system's ability to appropriately respond to viral infections. Arguments in favour of and against viral infections as major aetiological factors in T1D will be discussed in conjunction with potential pathological scenarios. More profound insights into the intricate relationship between viruses and their autoimmunity-prone host may lead ultimately to opportunities for early intervention through immune modulation or vaccination.

AIRE1A might be involved in cyclin B2 degradation in testicular lysates

The autoimmune regulator gene Aire shows predominant expression in thymus and other immunologically relevant tissues, and is assigned the major function of programming autoreactive T-cell deletion. However, the expression of this gene in tissues outside the immune system raises a question about its possible function beyond the T-cell deletion dogma. We detected Aire in mouse testis, and the expression of AIRE protein was remarkably high in postmeiotic germ cells. Sequencing results indicate that testis expressed Aire variant 1a. AIRE could be detected in spermatozoa, with heavy localization on the principal acrosomal domains. Mouse oocytes stained negatively for AIRE before fertilization, but stained positively for AIRE 30 min after fertilization. In the zygote, the levels of AIRE correlated negatively with cyclin B2 levels. Goat testicular lysates spiked with recombinant human AIRE exhibited augmented cyclin B2 degradation in the presence of protease inhibitors, which was inhibited by MG-132, indicating the operation of proteasomal pathways. Thus, this study identifies a correlation between the presence of AIRE and proteasomal breakdown of cyclin B2, which leads us to speculate that cyclin B2 could be a target of AIRE's E3-ubiquitin ligase activity.

Enteroviruses and type 1 diabetes: towards a better understanding of the relationship

Environmental factors, especially viruses, are involved in the initiation or the acceleration of type 1 diabetes (T1D) pathogenesis. Epidemiological data strongly suggest that enteroviruses, such as coxsackievirus B4 (CV-B4), can be associated with T1D. It has been demonstrated that enterovirus infections were significantly more prevalent in at risk individuals, such as siblings of diabetic patients, when they developed anti-beta-cell autoantibodies or T1D, and in recently diagnosed diabetic patients, compared with control subjects. The isolation of CV-B4 from the pancreas of diabetic patients strengthened the hypothesis of a relationship between the virus and the disease. Studies performed in vitro and in vivo in animal models helped to discover mechanisms of the infection of pancreas and other tissues, potentially able to play a role in the pathogenesis of T1D. Interestingly, it cannot be excluded that enteroviruses behave as half-devil half-angel since experimental studies suggest that, in certain conditions, these agents would be able to protect individuals against the disease. All of the plausible mechanisms by which enterovirus may be related to T1D will be reviewed here.

Role of coxsackievirus B4 in the pathogenesis of type 1 diabetes

Environmental factors, especially viruses, are thought to play an important role in the initiation or acceleration of the pathogenesis of type 1 diabetes (T1D). Data from retrospective and prospective epidemiological studies strongly suggest that enteroviruses, such as coxsackievirus B4 (CV-B4), may be associated with the development of T1D. It has also been shown that enterovirus infections are significantly more prevalent in at-risk individuals such as the siblings of diabetic patients, when they develop anti-beta-cell autoantibodies or T1D, and in recently diagnosed diabetic patients, compared with control subjects. The isolation of CV-B4 from the pancreas of diabetic patients supports the hypothesis of a relationship between the virus and the disease. Furthermore, studies performed in vitro and in vivo in animal models have increased our knowledge of the role of CV-B4 in T1D by helping to clarify the pathogenic mechanisms of the infection that can lead to beta-cell destruction, including direct virus-induced beta-cell lysis, molecular mimicry, 'bystander activation' and viral persistence. The role of enteroviruses as the sole agents in T1D, and a causal link between these agents and T1D, have not yet been established, although arguments that support such a role for these viruses in the pathogenesis of the disease cannot be ignored.