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.