The immune system is composed of two parts; the innate immune system and the acquired immune system. The two parts function together to protect the body from environmental insult and disease in a complex and dynamic process. While the components of the immune system are common among individuals, the immune system is personalized to our own unique experiences or exposure to our environment. The ability to adequately respond to an immune system challenge and mount an inflammatory response that protects, is fundamental to life. Sometimes, the normal inflammatory response does not return to normal resulting in a chronic inflammatory tone that is common to many chronic diseases such as vascular disease, diabetes, metabolic syndrome, neurological diseases, arthritis and many others (Serhan 2017). Health care professionals have an unprecedented opportunity to support the development of the immune system with personalized and customized nutritional care to enhance patient outcomes. The interplay of possible states of symbiosis and dysbiosis are impacted by diet, host genetics and infection or inflammation.
Innate Immune System: Ready to Go as a First Responder in Immune Protection
The innate immune system can be thought of as the “first responders” when a threat is recognized by cells of the innate immune system and an inflammatory response is triggered. The cells of the immune system are highly diverse but all have their origin in the bone marrow via the differentiation of hematopoietic stem cells to one of two pathways, the myeloid progenitor cells or lymphoid progenitor cells. (Schindler 2003) The myeloid progenitor cells further differentiate into monocytes, macrophages, erythrocytes, eosinophils, basophils, neutrophils and megakarycotes and platelets. The lymphoid progenitor cells differentiate into small white blood cells called lymphocytes such as T and B lymphocytes, natural killer cells, and dendritic cells.
The receptors of the innate immune cells constantly monitor the physiological exposure to environmental threat through microbial ligands (antigen presenting cells) and responds with threats to the body (foreign substances or pathogenic micro-organisms) by triggering or signaling the “first responders” to the scene. (Kieser and Kagan 2017) Of particular importance is the macrophage cell. The macrophage is a specialized leukocyte that can engulf foreign substances or pathogenic microorganisms in a process called phagocytosis. The macrophage is also involved in clearing dead and dying host cells in a process called efferocytosis. (Martin, Peters et al. 2014) In addition to the macrophages, other cellular factors involved in phagocytosis include monocytes and neutrophils that engulf and digest invading microorganisms in the phagocytosis process. After ingestion of the invading microorganisms, the macrophages express unique fragments of the partially digested pathogen on the surface of the macrophage membrane (surface receptors). The surface receptors trigger further recruitment of cells of the innate immune system to destroy the invading pathogen. Phagocytosis also triggers the transcription of pro-inflammatory signals (cytokines) from DNA to RNA in the nucleus of the cell which are then released into extracellular space for further recruitment of first responders. Increased membrane fluidity of the macrophage via dietary fatty acids is associated with an increase in engulfment and killing rate of macrophages in the innate immune system.(Schumann 2016)
The innate immune system protects the body from potential damage by an infectious agent that requires an immune response that could threaten life itself. The innate immune system is a non-specific defense that does not involve immunologic memory of pathogens. The innate immune system functions every day to protect us from harm and recognize self from non-self. There is new evidence that neutrophils play a protective role in chronic inflammation by cellular signaling with other immune and non-immune cells within tissues.(Soehnlein, Steffens et al. 2017).
The organs of the immune system are highly diverse and function to monitor threat and respond rapidly to protect against invasion of pathogenic organisms. The graphic from the National Cancer Institute nicely illustrates the organs of the immune system in the human body. (Schindler 2003)