Glossary of Immune System Terms and Terminology

Some of the general terms associated with infection and the immune system are listed below. It is recommended that you are familiar with these terms and terminology because infections and infection control is a major problem in healthcare.

  • Innate immune system: Naturally occurring immune mechanisms
  • Acquired immune system: Immune mechanisms that occur as the result of the antigen-antibody response
  • Nonspecific immune responses: The innate immune system's immune mechanisms
  • Specific immune responses: The acquired immune system's immune mechanisms
  • Germs: Microorganisms that cause infections
  • Pathogens: Microorganisms that cause infections
  • Chain of infection: The manner with which infections are transmitted and carried
  • The reservoir: The part of the chain of infection that is the environment or habitat, within which the pathogen lives, grows and reproduces. Reservoirs can include humans, animals, water, soil and insects.
  • Mode of transmission: The part of the chain of infection that allows a pathogen, or disease causing germ, to move from its reservoir to its susceptible host.
  • Direct contact transmission: The mode of transmission that occurs with direct contact with the pathogen
  • Droplet transmission: The mode of transmission that consists of direct contact with a spray of infectious material with can occur as the result of coughing and even speaking.
  • Indirect contact transmission: The mode of transmission that involves the movement of an infectious agent from the reservoir to the host with inanimate, or nonliving, objects
  • Airborne transmission: The mode of transmission that occurs when the pathogen is carried in dust or droplets in the air that remain in place for a sufficiently enough time to infect a person exposed to this air
  • Vehicle transmission: The mode of transmission that occurs when a person comes into contact with an infectious agent that is in water, blood, and even inanimate objects like a toy or a door knob
  • Vector transmission: The mode of transmission that entails a mode of transportation with a vector which, unlike vehicles, are live beings like ticks and mosquitoes that spread infections with relatively direct mechanical means like an insect bite
  • Bloodborne pathogens: Diseases causing pathogens that are spread and transmitted to others via contact with blood and other bodily fluids
  • Antibody is a protein in the blood that is produced as the result of an exposure to an antigen or pathogen. They are protective proteins that bind to antigens and destroy them
  • Antigen: A foreign and unnatural substance that provokes the body to produce antibodies to fight if off.
  • Immunization: The process with which a person becomes immune with an injection
  • Natural immunity: Immunity that is acquired in a natural way
  • Artificial immunity: immunity that is NOT acquired in a natural way
  • Active immunity: Immunity that occurs as the result of getting a particular infection and also by being given an immunization against the particular infection, both of which will lead to the body's production of antibodies against the particular infection. Active immunity is long lived.
  • Passive immunity: Immunity that occurs without the antigen-antibody response, but instead, with the direct receiving of antibodies
  • Bacteria: Singular cell beings that appear as spirals, rods, spheres and other shapes and can be pathogenic, leading to infection and also releasing tissue damaging toxins
  • Viruses: Pathogens are much smaller than bacteria; viruses have RNA, DNA and long molecules which comprise its genetic composition, a protein coat and an outer coating that contains lipids
  • Attachment: The first stage of viral growth
  • Penetration: The second stage of viral growth
  • Uncoating: The third stage of viral growth
  • Replication: The fourth stage of viral growth Self-assembly
  • Release: The fifth stage of viral growth
  • Fungi: Plant source microorganisms that affect human beings and typically classified as superficial, cutaneous, subcutaneous and systemic.
  • Superficial fungal infections: Fungal infections that affect and infect the skin's epidermis and the hair.
  • Cutaneous fungal infections: Fungal infections that include invasive hair and nail infections that goes beyond the epidermis
  • Subcutaneous fungal infections: Fungal infections that infect all layers of the skin to the muscles and the fascia
  • Systemic fungi infections: Fungal infections that can affect the entire body; these infections are typically highly virulent and they can spread to virtually all organs of the body
  • A prion: A nonliving pathogen that consists of an abnormal folding of normal cellular, or prion, proteins
  • A parasite: A living organism that lives on or in a host and gets its food from or at the expense of its host
  • Asepsis: Methods used to prevent the spread of infection. The two types of asepsis are medical asepsis, or clean procedure, and surgical, or sterile, asepsis.
  • Contaminated: Having been in contact with a microorganism. Sterile items are contaminated when sterile technique is not scrupulously followed and clean or medically aseptic items are contaminated when they have not been managed and handled to a manner that preserves the state of medical asepsis
  • Sterile/sterility: Free from all living microorganisms
  • Sterilization: The destruction of all microorganisms and large numbers of bacterial spores with the use of a chemical or physical sterilizer
  • Antiseptic: A germicidal solution that can be used on the skin to inhibit the growth of microorganisms, including pathogens
  • Cleaning: The physical, manual removal of visible material from a device or surface using scrubbing, water and a detergent or surfactant
  • Disinfection: The destruction of microorganisms including pathogens using a chemical or physical means of disinfection. Although disinfection destroys most pathogens, disinfection does not destroy spores.
  • Opportunistic infection: An infection caused by a microorganism that does not ordinarily cause disease but is capable of doing so under certain host conditions like a disease or disorder that adversely affects the person's immune system
  • Personal protective equipment (PPE): Specialized equipment and attire that is used by employees in healthcare to protect against infections. Examples of personal protective equipment include gowns, gloves, goggles and respirators.
  • Immunosuppression: Any disorder or treatment, like chemotherapy for cancer, that causes the immune system to be dysfunctional and not functioning correctly to protect the body
  • HIV/AIDS: Human immunodeficiency virus and autoimmune deficiency syndrome are viral infections that lead the immune system to be dysfunctional and not functioning correctly to protect the body
  • Hashimoto's thyroiditis: The autoimmune disorder that leads to thyroid gland damage and dysfunction
  • Rheumatoid arthritis: A type of arthritis that is caused by an autoimmune disorder
  • Systemic lupus erythematosus: Also referred to as lupus, this is a chronic autoimmune disorder that causes one's own immune system to destroy its own organs
  • Grave's disease: The disorder that affects the thyroid gland and increases its activity
  • Hashimoto's thyroiditis: An autoimmune disorder that leads to hypothyroidism, or low thyroid functioning
  • Addison's disease: An autoimmune disorder that leads to the lack of adrenal gland functioning
  • Rheumatoid arthritis: A type of arthritis that is caused by a systemic autoimmune disorder
  • Multiple sclerosis: A systemic autoimmune disorder that adversely affects the central nervous system

The Role of the Immune System

The primary role of the immune system is to fortify and protect the body from infection.

Unlike other systems of the body such as the urinary system, the cardiac system and the reproductive system, the immune system is spread throughout the body and not in only one area or region of the body.

The Parts of the Immune System

Two of the major parts and mechanisms of the immune system are the innate immune system and the acquired immune system. The term innate is defined as natural and normally occurring; and acquired is something that occurs for a reason other than a natural process that normally occurs.

The innate immune system consists of what are called nonspecific responses; and the acquired immune system consists of what are called specific responses. For example, a nonspecific response of the innate immune system is the skin, which as previously discussed with the Integumentary System, is the first line of defense against infections. As you know, the presence of skin is a naturally and normally occurring organ and part of the body, which is the definition of an innate immune system mechanism. On the other hand, acquired immune responses occur as the reaction to an antigen and an example of an acquired response of the acquired immune system is the activation of the T helper cells.

Other nonspecific responses include the hair, the inflammatory process, lymphocyte and phagocyte actions and other adaptive responses to the activity of antigens including the production of antibodies by the B cells and the destruction of pathogens by the T cells.

An antigen is a foreign and unnatural substance that provokes the body to produce antibodies to fight if off. Antigens are harmful to the body. An antibody is the substance that is produced by the body in response to the presence of an antigen. Antibodies prevent harm in terms of infections.

In addition to the acquired immune and innate immune systems, the immune system also consists of other protective mechanisms and structures such as immunity and the lymph glands, respectively. The lymph glands were previously discussed with the Circulatory System.

Some of the specific responses to infection include the immune systems' antibody mediated defenses and the cell mediated defenses or cellular immunity. Antibody mediated defenses include immunities including active immunity and passive immunity. Active immunity is characterized with the production of antibodies in response to an antigen; and passive immunity occurs when the host receives the antibodies to the antigen in an artificial manner with an immunization of antibodies or in a natural manner as occurs when immunity is passed from the mother to the fetus in utero or during the breast feeding process. Immunity that is naturally present and is not due to prior sensitization to an antigen from, for example, an infection or vaccination is considered innate.

The types of immunity are:

  • Natural immunity
  • Artificial immunity
  • Active immunity
  • Passive immunity

An antigen is a foreign and unnatural substance that provokes the body to produce antibodies to fight if off. Antigens are harmful to the body. An antibody is the substance that is produced by the body in response to the presence of an antigen. Antibodies prevent harm in terms of infections.

Natural immunity is defined as immunity that is acquired in a natural way. For example, a person develops immunity naturally by developing antibodies to an infection or disease, like measles, after they get this childhood infection and humans acquire natural immunity to some diseases and infections as they are developing in the mother's uterus.

Artificial immunity is defined as immunity that is NOT acquired in a natural way. For example, a person will have artificial immunity after they get an immunization against t an infection. Artificial immunity occurs when a person is immune against diphtheria, for example, after they get an immunization shot for diphtheria.

Active immunity, as mentioned above, occurs when the person produces antibodies. Active immunity can occur as the result of getting a particular infection and also by being given an immunization against the particular infection, both of which will lead to the body's production of antibodies against the particular infection.

Passive immunity is defined as the kind of immunity that occurs when a person gets antibodies with an injection of gamma globulin, an immunoglobulin of antibodies, and when a fetus gets antibodies in utero from the mother. Passive immunity is very short lived and temporary.

Below are examples of all the different types of immunity. Please note that examples of these different types of immunity are combinations of the four basic types of immunity discussed immediately above.

    • Active natural immunity: Developing antibodies as the result of having a particular infection. Active natural immunity occurs when a person gets an infection and, as the result of this infection, antibodies against it are developed in the person's body.
  • Active artificial immunity: Developing antibodies as the result of having a particular vaccine or immunization. Active artificial immunity occurs when a person gets an immunization of an antigen and, as the result of this immunization; antibodies against the antigen are developed in the person's body.
    • Passive natural immunity: Passive immunity does NOT involve an antigen-antibody production process. Passive immunity occurs when the person receives antibodies without the presence of antibodies. An example of passive natural immunity is when the fetus and the neonate have received antibodies from the mother against some infections as the result of this natural process.
  • Passive artificial immunity: Passive immunity does NOT involve an antigen-antibody production process. Passive immunity occurs when the person receives antibodies without the presence of any antigen. An example of passive natural immunity is when a person has gotten an immunization of antibodies, as is the case when a person gets an immunization of gamma globulin. Passive immunity is far less long lasting than active immunity. Passive immunity is temporary.

Infections

The immune system fights off infections that are NOT prevented by breaking the chain of infection

The chain of infection includes:

  • An agent
  • A reservoir
  • A mode of transmission
  • A portal of entry
  • A portal of exit
  • A susceptible host like a person that is at risk for an infection.

The chain of infection reflects the manner with which infections are transmitted and carried, as shown below:

Source: https://www.cdc.gov/ophss/csels/dsepd/ss1978/lesson1/section10.html

The reservoir, a part of the cycle of infection, is defined as the environment or habitat within which the pathogen lives, grows and reproduces. Reservoirs can include humans, animals, water, soil and insects.

A mode of transmission, or transportation, which is part of the cycle of infection, allows a pathogen, or disease causing germ, to move from its reservoir to its susceptible host. There are several modes of transmission including direct contact, indirect contact, the airborne route, the vehicle mode of transmission and the vector mode of transmission.

Direct transmission can occur with direct contact with the pathogen and also with a spread of an infectious droplet. Depending on the pathogen, direct contact can occur with skin, mucous membrane contact as well as from contact with infectious material such as soil or water.

Droplet spread consists of direct contact with a spray of infectious material with can occur as the result of coughing and even speaking. Examples of pathogens that spread with direct contact include parasitic diseases such as tapeworm, and others, such as mononucleosis and childhood diseases like pertussis.

Indirect transmission involves the movement of an infectious agent from the reservoir to the host with inanimate objects. Examples of inanimate objects that can spread infections are door knobs, kitchen counter tops, toilet seats and children's play things like toys.

Airborne transmission occurs when the pathogen is carried in dust or droplets in the air that remain in place for a sufficiently enough time to infect a person exposed to this air. Measles is an example of a virus that is transmitted with the airborne mode of transmission.

Vehicle transmission occurs when a person comes into contact with an infectious product that is in water, blood, and even inanimate objects like a toy or a door knob.

Vector transmission entails a mode of transportation with a vector. Vectors, unlike vehicles, are live beings like ticks and mosquitoes that spread infections with relatively direct mechanical means like an insect bite.

The portal of entry is the "open door" through which the pathogen enters the susceptible host and comes in contact with an environment that is favorable to their reproduction and growth. The portal of entry is most often identical to the portal of exit. For example, hepatitis B and C use the blood and other bodily fluids as both their portal of entry and their port of exit.

The most common portals of entry include the respiratory tract through a droplet of airborne mode of transmission, the gastrointestinal tract with transmission via the fecal-oral route, though the skin and mucous membranes, with direct contact, and the blood and other bodily fluids using these portals of entry as their same portal of exit.

In contrast the portal of entry, the portal of exit is the "exit door" with which the pathogen leaves the body. Again, the portal of exit is very often identical to the portal of entry.

The last part of the chain of infection is the susceptible host. Simply defined, a susceptible host is defined as a person who is not able to resist the infection when they are exposed to it. Many factors impact on susceptibility; some of these factors are related to the pathogen and its level of infectiousness, and other factors that are individual to the host person. For example, it takes a higher level of susceptibility to resist a pathogen that is highly virulent and with a high level of pathogenicity.

Pathogens

There are a wide variety of microorganisms that can cause infections and diseases among humans and there are also a wide variety of microorganisms that do not lead to infections and diseases, and there are also some that are highly beneficial to humans in terms of health. It is the pathogenic, or disease causing, agents that infection control aims to eliminate.

The different kinds pathogens are:

  • Bacteria
  • Viruses
  • Fungi, the pleural form of fungus
  • Prions
  • Parasites

Bacteria

Bacteria are singular cell beings that appear as spirals, rods, spheres and other shapes. Some are pathogenic, leading to infection and also releasing tissue damaging toxins; others are highly beneficial to the body. Some examples of bacteria include streptococcus, staphylococcus and Escherichia coli.

Some bacteria are classified as gram positive because they react to a gram stain; these gram positive microbes have thick walls containing teichoic acid and peptidoglycan. Others are classified as gram negative because they do not react to a gram stain. These microbes, more common than gram positive bacteria, have thinner walls than gram positive bacteria. Bacteria are also differentiated by their ability to resist color changes when subjected to a staining procedure in the laboratory. Acid fast bacteria resist decolorization when stained .

The four phases of bacterial growth are the lag phase, the log phase, the stationary phase and the death phase in that sequential order.

Examples of bacterial infections are listed in the picture above.

Viruses

Viruses, which are much smaller than bacteria, have RNA, DNA and long molecules which comprise its genetic composition, a protein coat and an outer coating that contains lipids.

Viruses, like bacteria, can be categorized and classified in several ways. For example, they can be categorized as:

  • DNA viruses which include both single and double stranded DNA viruses
  • RNA viruses which include single and double stranded RNA viruses

The six stages of virus growth in the correct sequential order are:

  1. Attachment
  2. Penetration
  3. Uncoating
  4. Replication
  5. Self-assembly
  6. Release

Fungi

Fungi Aspergillus, black mold, which produce aflatoxins, cause pulmonary infection aspergillosis and lesions of other location. 3D illustration.

There are an enormous number of fungi in our natural environment including those in the soil, plant life and on human beings. Fortunately, the vast majority of fungi are harmless; however, there are some that can lead to serious infections among humans, particularly when their immune system is compromised and not able to ward these infections off.

Fungi that affect human beings are typically classified as superficial, cutaneous, subcutaneous and systemic.

Superficial fungal infections affect and infect the skin's epidermis and the hair. These infections can often occur among healthy people. An example of a superficial fungal infection is tinea capitis which is often referred to as ringworm of the scalp because it takes on the appearance of a worm despite the fact that it is caused by a fungus.

Cutaneous fungal infections include invasive hair and nail infections that go beyond the epidermis. An example of a cutaneous fungal disease is athlete's foot, or tinea pedis.

Subcutaneous fungal infections can infect all layers of the skin to the muscles and the fascia. These fungal infections, often serious, typically result from a deep puncture wound.

Systemic fungi infections are typically highly virulent and they can lead to serious consequences including death as they can potentially spread to and infect virtually all organs of the body. Those with immunosuppression as the result of HIV, chemotherapy and cancer are at greatest risk for systemic fungi infections. Some examples of systemic fungal infections include aspergillosis, candidiasis and cryptococcosis.

Prions

A prion is not a living organism; it is defined as an abnormal folding of normal cellular, or prion, proteins. Some of the infectious diseases associated with prions include encephalopathy, including "mad cow" disease, other rare diseases.

Prions and prion diseases primarily affect the brain and neural tissue; these infections are associated with a high morbidity and mortality rate without a possible cure. Prions can be destroyed only with sterilization.

Parasites

A parasite is an organism that lives on or in a host and gets its food from or at the expense of its host. Parasites can cause disease in humans. Some parasitic diseases are easily treated and some are not. The burden of these diseases often rests on communities in the tropics and subtropics, but parasitic infections can also affect people in developed countries as well.

Some examples of parasitic infections include giardia, tapeworms, pin worms, lice infestations, maggot infestation and scabies.

Infection Control: Asepsis

Asepsis is a method that is used to control and to prevent the spread of infection. The two types of asepsis are medical asepsis, or clean procedure, and surgical, or sterile, asepsis.

Medical Asepsis

Formally known as "clean technique," medical asepsis is an infection control practice that decreases and reduces the spread, number, and growth of microorganisms, including pathogens that have the potential to cause infection. Medical asepsis is used for procedures such as client hygiene and the administration of oral medications, for example.

Surgical Asepsis and Sterile Technique

Unlike medical asepsis, surgical asepsis eliminates all microorganisms including spores. This infection control practice is also referred to as sterile technique. Generally speaking, surgical asepsis is used when internal areas are cared for and when the skin is not intact.

For example, surgical asepsis is used for wound care in the operating room and other areas where invasive procedures are done, and for nursing procedures such as the administration of intravenous medications and the insertion of an indwelling urinary catheter. Skin cannot be sterilized but only disinfected using medical asepsis.

Most healthcare acquired infections are spread with the hands of the health care workers from one patient to another.

The most commonly occurring risk factors for hospital and healthcare acquired infections are prolonged illness and immunosuppression, which can result from an infection like HIV, treatments, such as chemotherapy, and some medications.

Additionally, all pieces of equipment and nonsterile supplies, such as blood pressure cuffs, can harbor and spread hospital and healthcare acquired infections. Hospital and healthcare acquired infections are costly and they can, for the most part, be prevented.

The urinary tract, the respiratory tract, wounds, and the bloodstream are the most common sites for hospital and healthcare acquired infections.

Hand Washing

Hand hygiene consists of handwashing with plain soap or an antimicrobial soap and water as well as the use of alcohol based hand products.

Handwashing is the single most effective way to prevent healthcare acquired infections.

Protective precautions, such as standard precautions and transmission based precautions, are also necessary to prevent the spread of these deadly infections which is extremely important because of the presence of so many resistant strains of pathogens that do not respond to antibiotics.

Handwashing is done with soap, water, and friction for a minimum of 15 to 20 seconds before and after each client contact, in addition to other times such as before and after donning and removing gloves. When an alcohol based product is used, all surfaces of the hands are rubbed until the entire product dries completely.

Standard Precautions

Standard precautions apply to all blood and bodily fluids and all clients regardless of the person's diagnosis and even when the client has expired. These precautions include handwashing and the use of personal protective equipment (PPE) such as goggles, gowns, gloves and masks when the risk of contact with these fluids is reasonably anticipated.

Special and Transmission Based Precautions and Isolation

Contact precautions are used to prevent any direct and indirect contact transmission of infections, such as those contained in diarrhea, wounds, and blood. These precautions include the use of gloves and a gown, as indicated.

Airborne precautions are used for the prevention of airborne transmission microbes like tuberculosis. These precautions include a special HEPA mask and a negative pressure room.

Droplet precautions are used to prevent the transmission of pathogens that are transmitted with a cough or sneeze. The use of goggles or a mask, but not a special HEPA mask, is used for droplet precautions.

Personal Protective Equipment (PPE)

Specialized equipment and attire that is used by employees in healthcare to protect against infections. Examples of personal protective equipment include gowns, gloves, goggles and respirators.

Disorders Affecting the Immune

  • Immunosuppression
  • HIV/AIDS
  • Hashimoto's thyroiditis
  • Rheumatoid arthritis
  • Systemic lupus erythematosus
  • Grave's disease
  • Hashimoto's thyroiditis
  • Addison's disease
  • Rheumatoid arthritis
  • Multiple sclerosis

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