Involvement of trained immunity during autoimmune responses.

Recently, it has been described that innate immune cells such as monocytes, macrophages, and natural killer cells can develop a non-specific immune response induced by different stimuli, including lipopolysaccharides, Mycobacterium bovis Bacillus Calmette-Guérin, and oxidized low-density lipoprotein. This non-specific immune response has been named "trained immunity," whose mechanism is essential for host defense and vaccine response, promoting better infection control. However, limited information about trained immunity in other non-infectious diseases, such as autoimmune illness, has been reported. The complexity of autoimmune pathology arises from dysfunctions in the innate and adaptive immune systems, triggering different clinical outcomes depending on the disease. Nevertheless, T and B cell function dysregulation is the most common characteristic associated with autoimmunity by promoting the escape from central and peripheral tolerance. Despite the importance of adaptative immunity to autoimmune diseases, the innate immune system also plays a prominent and understudied role in these pathologies. Accordingly, epigenetic and metabolic changes associated with innate immune cells that undergo a trained process are possible new therapeutic targets for autoimmune diseases. Even so, trained immunity can be beneficial or harmful in autoimmune diseases depending on several factors associated with the stimuli. Here, we reviewed the role of trained immunity over the innate immune system and the possible role of these changes in common autoimmune diseases, including Systemic Lupus Erythematosus, Rheumatoid Arthritis, Multiple Sclerosis, and Type 1 Diabetes.

Mora VP ，Loaiza RA ，Soto JA ，Bohmwald K ，Kalergis AM ... -  《-》

Trained Immunity Contribution to Autoimmune and Inflammatory Disorders.

A dysregulated immune response toward self-antigens characterizes autoimmune and autoinflammatory (AIF) disorders. Autoantibodies or autoreactive T cells contribute to autoimmune diseases, while autoinflammation results from a hyper-functional innate immune system. Aside from their differences, many studies suggest that monocytes and macrophages (Mo/Ma) significantly contribute to the development of both types of disease. Mo/Ma are innate immune cells that promote an immune-modulatory, pro-inflammatory, or repair response depending on the microenvironment. However, understanding the contribution of these cells to different immune disorders has been difficult due to their high functional and phenotypic plasticity. Several factors can influence the function of Mo/Ma under the landscape of autoimmune/autoinflammatory diseases, such as genetic predisposition, epigenetic changes, or infections. For instance, some vaccines and microorganisms can induce epigenetic changes in Mo/Ma, modifying their functional responses. This phenomenon is known as trained immunity. Trained immunity can be mediated by Mo/Ma and NK cells independently of T and B cell function. It is defined as the altered innate immune response to the same or different microorganisms during a second encounter. The improvement in cell function is related to epigenetic and metabolic changes that modify gene expression. Although the benefits of immune training have been highlighted in a vaccination context, the effects of this type of immune response on autoimmunity and chronic inflammation still remain controversial. Induction of trained immunity reprograms cellular metabolism in hematopoietic stem cells (HSCs), transmitting a memory-like phenotype to the cells. Thus, trained Mo/Ma derived from HSCs typically present a metabolic shift toward glycolysis, which leads to the modification of the chromatin architecture. During trained immunity, the epigenetic changes facilitate the specific gene expression after secondary challenge with other stimuli. Consequently, the enhanced pro-inflammatory response could contribute to developing or maintaining autoimmune/autoinflammatory diseases. However, the prediction of the outcome is not simple, and other studies propose that trained immunity can induce a beneficial response both in AIF and autoimmune conditions by inducing anti-inflammatory responses. This article describes the metabolic and epigenetic mechanisms involved in trained immunity that affect Mo/Ma, contraposing the controversial evidence on how it may impact autoimmune/autoinflammation conditions.

Funes SC ，Rios M ，Fernández-Fierro A ，Di Genaro MS ，Kalergis AM ... -  《Frontiers in Immunology》

Anti-inflammatory Trained Immunity Mediated by Helminth Products Attenuates the Induction of T Cell-Mediated Autoimmune Disease.

Quinn SM ，Cunningham K ，Raverdeau M ，Walsh RJ ，Curham L ，Malara A ，Mills KHG ... -  《Frontiers in Immunology》

Trained immunity - basic concepts and contributions to immunopathology.

Trained immunity is a functional state of the innate immune response and is characterized by long-term epigenetic reprogramming of innate immune cells. This concept originated in the field of infectious diseases - training of innate immune cells, such as monocytes, macrophages and/or natural killer cells, by infection or vaccination enhances immune responses against microbial pathogens after restimulation. Although initially reported in circulating monocytes and tissue macrophages (termed peripheral trained immunity), subsequent findings indicate that immune progenitor cells in the bone marrow can also be trained (that is, central trained immunity), which explains the long-term innate immunity-mediated protective effects of vaccination against heterologous infections. Although trained immunity is beneficial against infections, its inappropriate induction by endogenous stimuli can also lead to aberrant inflammation. For example, in systemic lupus erythematosus and systemic sclerosis, trained immunity might contribute to inflammatory activity, which promotes disease progression. In organ transplantation, trained immunity has been associated with acute rejection and suppression of trained immunity prolonged allograft survival. This novel concept provides a better understanding of the involvement of the innate immune response in different pathological conditions, and provides a new framework for the development of therapies and treatment strategies that target epigenetic and metabolic pathways of the innate immune system.

Ochando J ，Mulder WJM ，Madsen JC ，Netea MG ，Duivenvoorden R ... -  《-》

BCG-induced trained immunity: history, mechanisms and potential applications.

The Bacillus Calmette-Guérin (BCG) vaccine was discovered a century ago and has since been clinically applicable. BCG can not only be used for the prevention of tuberculosis, but also has a non-specific protective effect on the human body called trained immunity that is mediated by innate immune cells such as monocytes, macrophages, and natural killer cells. Mechanisms of trained immunity include epigenetic reprogramming, metabolic reprogramming, and long-term protection mediated by hematopoietic stem cells. Trained immunity has so far shown beneficial effects on cancer, viral-infections, autoimmune diseases, and a variety of other diseases, especially bladder cancer, respiratory viruses, and type 1 diabetes. The modulation of the immune response by BCG has led to the development of a variety of recombinant vaccines. Although the specific mechanism of BCG prevention on diseases has not been fully clarified, the potential role of BCG deserves further exploration, which is of great significance for prevention and treatment of diseases.

Chen J ，Gao L ，Wu X ，Fan Y ，Liu M ，Peng L ，Song J ，Li B ，Liu A ，Bao F ... -  《Journal of Translational Medicine》