Is There a Connection Between Autoimmune Diseases and the Microbiome?

The connection between autoimmune diseases and the microbiome is a topic of increasing interest in the field of immunology. Recent studies suggest that alterations in the balance of microorganisms residing in the gut can lead to significant changes in the immune system, potentially contributing to the onset of various autoimmune conditions.

Role of Activated DCs and T Cells

The immune system's function is closely linked with the makeup of the microbiome. Activated dendritic cells (DCs) play a pivotal role in the differentiation and activation of T cells, which are crucial for immune tolerance and regulation. According to Shi et al. (2017), DCs can stimulate the differentiation of T cells into various subsets, such as Th1, Th2, and Th17 cells, depending on the specific stimuli received.

The intestinal mucosa is home to a high concentration of T cells, which can be categorized into two main subpopulations: Type A or conventional TCRαβ T cells, primarily located at PPs (Peyer's patches) and mesenteric lymph nodes, and Type B or non-conventional TCRγδ T cells, which are predominantly found at the epithelium (van Wijk and Cheroutre, 2010).

Regulation of Immune Responses

Nave T cells differentiate into effector helper T cells (Th), including different subsets such as Th1, Th2, and Th17 cells, which play crucial roles in immune responses. Th1 cells target intracellular pathogens, Th2 cells protect against parasites and mediate allergic reactions, and Th17 cells clear foreign pathogens (Geremia et al., 2014).

Intestinal DCs also regulate the differentiation of T cells into regulatory T cells (Tregs). Tregs are essential for controlling the immune response, particularly by suppressing the activation and proliferation of T helper cells via the secretion of anti-inflammatory cytokines (Ogarra and Vieira, 2004).

Imbalance Between T Helper and Treg Cells

Several studies support the notion that an imbalance between T helper (Th) and Treg cells is closely associated with intestinal autoimmune pathologies (Fasching et al., 2017). The diagram (Figure 11) illustrates this relationship, highlighting the critical role of Tregs in maintaining immune tolerance.

Intestinal Microbiota and Its Influence on Non-Gastrointestinal Autoimmune Diseases

The impact of gut microbiota on non-gastrointestinal autoimmune diseases is a complex but significant area of research. The gut microbiota can influence various systems in the body, including the brain, cardiovascular system, and nervous system, through mechanisms such as intestinal permeability.

As mentioned, changes in microbiota diversity and balance can lead to physiological changes that are not limited to the gastrointestinal system. Gut microbiota has a profound influence on immune function, which can in turn impact the entire body. A healthy balance of gut microbiota is essential for both digestive health and a robust immune system.

Conditions resulting from gut microbiota imbalances and dysregulation can include autoimmune diseases, hyperimmune conditions, cardiovascular diseases, chronic neurological disorders, and even certain cancers and psychiatric conditions.

Systemic Effects of Gut Microbiota and Its Relationship with Disease and Modulation

Intestinal permeability is a key mechanism by which gut microbiota can affect the systemic immune response. When the intestinal barrier is compromised due to pathogen overgrowth or stress, intestinal permeability increases, allowing gut microbiota to enter the systemic circulation. This phenomenon, often referred to as "leaky gut" syndrome, can lead to systemic immune reactions and influence the development of various diseases.

A healthy gut microbiome contributes to a balanced immune system, which in turn supports overall health. Modulation of the gut microbiome through dietary interventions, probiotics, and other methods can help maintain a healthy balance and ward off disease. Further research is needed to fully understand the mechanisms and potential treatments for autoimmune diseases associated with an imbalanced microbiome.