Immune System

Neutrophil and MRSA
Immune system cell called a neutrophil (purple) ingesting MRSA bacteria (yellow). NIAID

Immune System Function

There's a mantra in organized sports that says, defense is king! In today's world, with germs lurking around every corner, it pays to have a strong defense. I'm talking about the body's natural defense mechanism, the immune system. The function of this system is to prevent or reduce the occurrence of infection. This is accomplished through the coordinated function of the body's immune cells.

Cells of the immune system, known as white blood cells, are found in our bone marrow, lymph nodes, spleen, thymus, tonsils, and in the liver of embryos. When microorganisms, such as bacteria or viruses invade the body, non-specific defense mechanisms provide the first line of defense.

Innate Immune System

The innate immune system is a non-specific response that includes primary deterrents. These deterrents ensure protection against numerous germs and parasitic pathogens (fungi, nematodes, etc.). There are physical deterrents (skin and nasal hairs), chemical deterrents (enzymes found in perspiration and saliva), and inflammatory reactions (initiated by immune cells). These particular mechanisms are named appropriately because their responses are not specific to any particular pathogen. Think of these as a perimeter alarm system in a house. No matter who trips the motion detectors, the alarm will sound.

White blood cells involved in the innate immune response include macrophages, dendritic cells, and granulocytes (neutrophils, eosinophils, and basophils). These cells respond immediately to threats and are also involved in the activation of adaptive immune cells.

Adaptive Immune System

In cases where microorganisms get through the primary deterrents, there is a back-up system called the adaptive immune system.

This system is a specific defense mechanism in which immune cells respond to specific pathogens and also provide protective immunity. Like innate immunity, adaptive immunity includes two components: a humoral immune response and a cell mediated immune response.

Humoral Immunity

The humoral immune response or antibody‐mediated response protects against bacteria and viruses present in the fluids of the body. This system uses white blood cells called B cells, which have the ability to recognize organisms that don't belong to the body. In other words, if this isn't your house, get out! Intruders are referred to as antigens. B cell lymphocytes produce antibodies that recognize and bind to a specific antigen to identify it as an invader that needs to be terminated.

Cell Mediated Immunity

The cell mediated immune response protects against foreign organisms that have managed to infect body cells. It also protects the body from itself by controlling cancerous cells. White blood cells involved in cell mediated immunity include macrophages, natural killer (NK) cells, and T cell lymphocytes. Unlike B cells, T cells are actively involved with the disposal of antigens. They make proteins called T cell receptors that help them recognize a specific antigen.

There are three classes of T cells that play specific roles in the destruction of antigens: Cytotoxic T cells (which directly terminate antigens), Helper T cells (which precipitate the production of antibodies by B cells), and Regulatory T cells (which suppress the response of B cells and other T cells).

Immune Disorders

There are serious consequences when the immune system is compromised. Three known immune disorders are allergies, severe combined immunodeficiency (T and B cells are not present or functional), and HIV/AIDS (severe decrease in the number of Helper T cells). In cases involving autoimmune disease, the immune system attacks the body's own normal tissues and cells. Examples of autoimmune disorders include multiple sclerosis (affects the central nervous system), rheumatoid arthritis (affects joints and tissues), and graves disease (affects the thyroid gland).

Lymphatic System

The lymphatic system is a component of the immune system that is responsible for the development and circulation of immune cells, specifically lymphocytes. Immune cells are produced in bone marrow. Certain types of lymphocytes migrate from bone marrow to lymphatic organs, such as the spleen and thymus, to mature into fully functioning lymphocytes. Lymphatic structures filter blood and lymph of microorganisms, cellular debris, and waste.