An Overview of The Human Immune System
The human immune system is made up of two major components – the nonspecific (innate) immune system and the adaptive (targeted/specific) immune system. These two components of the immune system work in co-operation to defend the body against invading and harmful organisms such as parasites, fungi, bacteria and viruses.
The First Line of Defense in the Anti-Disease System
The primary component of a person’s immunity (first line of defense) is made up further of two parts – the first being the skin and mucous membranes (physical barrier). If the external skin barrier has been compromised, the second layer of defense is then activated in response. The major indicator of the activation of the secondary defense system is inflammation – which is characterized by a localized redness and swelling wherever the invading organisms are present. It is also systemically marked by a raise in body temperature (fever) and the presence of pus around the infected area and possibly the presence of white blood cells in the urine.
A raised body temperature (fever) is one of the ways that the body maintains its homeostasis (balance) so that all of the chemical reactions that take place in the body occur in a place of optimum efficiency, and this is necessary for achieving ultimate wellness and health. A raised body temperature aids in destroying foreign organisms.
Parts of the Primary Defense System
The different constituents of the primary defense system include the following:
Phagocytes – these include macrophages and neutrophils. Their job is to chiefly ingest and in doing so, destroy invading harmful pathogens. The process whereby a phagocyte emerges from the bloodstream and into the tissues to ingest invading organisms is called phagocytosis. This is done by the phagocyte recognizing the harmful organism, and locking onto it, and thereby ingesting it. Some bacteria mask their identities, and can confuse phagocytes; the immune system can overcome this by covering pathogens with opsonins. These are complement proteins that then give “handles” for the phagocytes to lock onto invading pathogens and thereby destroy them. In the case where certain pathogens are resistant to these, the immune system then reacts by providing additional supports – helper T cells release chemicals that stimulate the macrophages, which then release additional destructive enzymes that are lethal to these pathogens. Neutrophils also pierce the invasive organism’s membrane by using defensins. When phagocytes are unable to ingest the invading organisms, they release their toxic weapons into the extracellular fluid, which then destroys these pathogens. Neutrophils destroy themselves in the process of eradicating pathogens, but macrophages can continue to destroy invasive substances.
Natural Killer Cells – are present in the bloodstream and also the lymphatic system. These cells can lyse and subsequently destroy cancer cells and virus infected body cells before the adaptive immune system is switched on. They are part of a group of cells called large granular lymphocytes. They can eradicate a large number of foreign harmful cells and organisms, and they are non-specific in their destructive targeting. Natural killer cells destroy harmful cells by contacting them and causing programmed cell death (also known as apoptosis). They also give off strong chemicals which promote the body’s inflammatory response.
Inflammation is part of the primary defensive immune system. It is activated by the external trauma to body tissues, or via intense heat (resulting in burns), chemical irritation to the skin, or infection by fungi, viruses and bacteria. The inflammatory response results in several resultant effects: prevention of spread of infection; disposal of dead cells and destroyed pathogens; alert of immune system and foundation for tissue and cellular repair. It begins with a chemical alarm – chemicals being released into the extracellular fluid – these are released from injured or stressed cells. These can also be triggered by the release of certain proteins in the blood (histamine response). Macrophage cells (and certain other tissues) have special detection abilities which can then activate the immune system. The other effect of inflammation includes the dilation of the blood vessels around the infection, allowing more blood flow to the area, which promotes rapid healing. The blood vessels and surrounding tissues also become more permeable, allowing for the migration of immune system cells more rapidly to the affected body part. Exudate is the resultant fluid from the increased movement of cells and blood to the affected area, and this causes localized swelling. This fluid can press against nerve endings, causing the pain response. Phagocyte mobilization occurs as a result of inflammation, and invading organisms are destroyed.
The Secondary Response System
The Adaptive (or Secondary) Component of a person’s immunity is the body’s built in specific immune response, which is acquired throughout a person’s lifetime of exposure to various invading organisms. The adaptive immune system is activated after the immediate response of the primary immune system response, and acts for longer than the primary immune defense. The theory of immunization, by the initial exposure of a person to a dead or disabled pathogen, and its resultant effect being that the immune system develops antigens specific to that pathogen operates within the secondary defense system.
The secondary adaptive immune system is a targeted immunity to various organisms, and its activation causes the body to react and destroy any specific pathogen it has been programmed to respond to. It prevents reinfection by the same organisms. Often the secondary immune system will have been activated without a person being aware, they may have very mild symptoms of malaise for 24 hours or less, and that is the secondary immune system destroying a recognized pathogen.
Immunisation programs are vital in helping to prevent the spread of many diseases, because it provides a targeted community wide response to the prevention of some very harmful diseases. Once an immune system has been programmed, it will destroy any recognized pathogen that it has been previously exposed to. This secondary targeted immunity takes time to develop, and that is why immunization programs are extremely effective in the prevention of disease.