Gut flora and its role in immune function

BYST.DR: HARITH RIYADH AKAKI TSERETELI ATSTE UNIVERSITY

Although the main functions of the digestive system were once believed to include little beyond the breakdown of food into usable energy for the body and elimination of waste, the digestive tract is also home to 100 trillion microorganisms, known as the gut flora

The majority of these microorganisms are bacteria, with a small percentage consisting of fungi and protozoa.

What is gut flora

1.) Essential Flora: This is the "friendly" bacteria that is found in the gut. In the healthy individual, essential flora dominates and controls other types of less desirable microorganisms. When functioning normally, this type of flora is responsible for conducting numerous roles that keep the body healthy.

2.) Opportunistic Flora: This group of microbes is found in the gut in limited numbers that are strictly controlled by the essential flora in the healthy individual. This type of flora is capable of causing disease if the essential flora becomes compromised and is unable to control the growth and numbers of opportunistic flora.

3.) Transitional Flora: These are various microorganisms that are introduced into the body through eating and drinking. When the essential flora is healthy and functioning normally, this type of flora will pass through the digestive track without causing harm. However, if the essential flora is damaged, this group of microbes can cause disease.

Types of Gut Flora which found in the gut:

Although there is still much to be learned about the role of gut flora in immune function, it is becoming increasingly clear that disease (and health) really does begin in the gut! Studies have shown that the gut flora has a profound influence on the development and maturation of the immune system after birth (Bouskra et al., 2008; Macpherson & Harris, 2004). In addition, it has been estimated that approximately 80 -85% of the immune system is located in the gut.

Gut Flora and Immune Function

In the healthy individual, the essential gut flora forms a bacterial layer that covers the entire digestive track. This bacterial layer acts as a physical barrier to protect against transitional flora , viruses, parasites, toxins, and undigested food particles. The gut flora produces acids that lower the pH of the gut wall and make it undesirable for microbes that cause disease. The essential flora also has the ability to neutralize many toxins and inactivate carcinogens (substances known to cause cancer). It also plays a direct role in suppressing the processes by which cancer cells are known to develop and grow

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The essential flora has a direct effect on important immune functions because it is responsible for stimulating the tissues of the lymph system that are located in the gut wall to produce lymphocytes, a type of white blood cell that fights infections. The lymphocytes then produce immunoglobulins, which are antibodies formed in response to contact with foreign substances (viruses, bacteria, fungi, etc). The immunoglobulins destroy and inactivate invading substances that enter the body through food and drink

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The essential flora also has a direct impact on the function and/or production of other many other cells of the immune system. When the essential flora is damaged, immune function is affected not only in the gut, but systemically as well (throughout the entire body). Specific to autoimmune disease, essential gut flora plays an important role in the development of regulatory T cells, a critical component of the immune system. The types, number, and balance of regulatory T cells are directly influenced by the essential gut flora. The dysfunction of the regulation of different types of regulatory T cells (an imbalance in certain kinds of T cells) is responsible for the development of autoimmune disease.

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A broader explanation of how the gut flora influences immune function is by understanding the balance between the two arms of the adaptive immune response, known as Th1 and Th2 immunity.

In general, the role of Th1 immunity is to fight infections in the skin, mucous membranes, and cells. When the essential flora is damaged, the production and function of Th1 cells becomes impaired, allowing more invaders into the body. The body responds by overcompensating with a Th2 response. The overactive Th2 response then predisposes the individual to allergic-type reactions, chronic inflammation, and autoimmunity. Healthy essential gut flora is the key to keeping these arms of the adaptive immune system in balance, thus preventing disease.

how the gut flora influences immune function