Study links muscle mass with strong immune system

The immune system of the human body is what protects us from attacks by bacteria, viruses, parasites and various other pathogens. The immune system is made up of several tiny cells and tissues, which guard against invading pathogens and prevent them from infecting the body. Even the dead cells of the human body, or the malfunctioning ones, are identified by the immune system and replaced by healthy, functioning ones.

The latest study, performed by scientists at the German Cancer Research Center in Heidelberg performed a series of tests on mice to evaluate how muscle mass is responsible for a robust immune system in the body. Some of the cells responsible for a strong immune response against illnesses in the body are known as T cells, which become impaired or weakened by cachexia.

Many viral infections and diseases such as cancers result in the overwhelming loss of body weight that also leads to muscle atrophy, the primary cause of cachexia. A type of T cells known as CD8+ become impaired during such infections, which is the common factor between the condition and the loss of muscle mass in the body.

The mice in the study were infected with the lymphocytic choriomeningitis virus in order to study the gene expression in their skeletal muscles. They observed that when the infection attacked the muscle cells of the mice, they began to release cytokines named interleukin-15 (IL-15), which is responsible for the development of inflammatory and protective immune responses to pathogens.

The IL-15 are a type of proteins or peptides that regulate cell response and act as precursors of T cells in the skeletal muscles of the body. When the body is attacked by a pathogen, they protect the T cells fighting the infection. According to the lead scientist of the study, the precursor cells can migrate from the muscles and develop into T cells to replace the ones that are losing their function while fighting the infection.

The study found out that mice that had more muscle mass were able to deal with the viral infection more effectively than those who had weaker muscles. The researchers, however, did not surmise that this would hold true even in the case of humans, and that further research was necessary to establish this relationship.

The scientists were also not able to ascertain how these precursor cells developed in the skeletal muscle mass that preserve the functioning of the T cells, sustaining the immune response for a longer period of time.

Several types of cells, proteins, tissues and organs make up the body's immune system, which not only helps identify any foreign body entering the system but also fights off pathogens that attack the body as well. The white blood cells (WBC), also known as leukocytes, run through the blood vessels all over the body and multiply when they come across a pathogen trying to cause an infection.

The leukocytes are further divided into two main types, known as phagocytes that absorb pathogens to kill them off, and lymphocytes, which aid the body in remembering previous pathogens and infections, helping to identify them in case of a recurrence. It is these lymphocytes that also become T lymphocytes or T cells. The T cells also have two different types: the helper T cells that are responsible for the immune response and killer T cells, which attack and kill off other cells, and take charge while fighting off viruses.

The lymphocytes, in turn, are responsible for identifying the antigen entering the body and releases antibodies to fight them off, and the B lymphocytes or the B cells are responsible for this function. 

Immunity of a human body is subdivided into further types, such as the immunity we are all born with, some that are acquired with age and vaccination, and passive immunity, which is taken from another source, like a newborn baby which gets this from the mother through the placenta as well as breast milk after birth.

Another study, published in 2016 in the journal Immunity, found out that certain immune cells in the body also produce certain types of protein that lead to the formation of new muscle fibres, especially after suffering a muscle injury or tear. 

A study published in the Journal of Sport and Health Science in 2019 also found that acute exercise improves the immune response and the body's defence activity, and that regular exercise improves immune regulation in the body while delaying age-related degeneration and dysfunction.