Immune System

Active immunity vs. Passive immunity:

Active immunity is the development of antibodies in response to stimulation by an antigen. Naturally acquired active immunity occurs when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response. Artificially acquired active immunity can be induced by a vaccine, a substance that contains the antigen.

Passive immunity, once formed, those antibodies can be removed from the host and transferred into another recipient where they provide immediate passive immunity. It is acquired by the injection into the host of serum containing antibodies that have been formed by a donor organism itself possessing active immunity to the disease.

The two are similar because they both are used to treat specific areas of the body, but they way they get to the area is the difference.

Innate immunity vs. adaptive immunity: Innate-nonspecific/Adaptive-specific

Innate immunity is inherited as part of the structure of the organism. It distinguishes between "self" and "non-self" by recognizing molecules called pathogen-associated molecular patterns. This is the first line of defense against and invading pathogen; which include epithelial barriers, high acidity of gastric juices, phagocytosis, interferons, and fever. Innate immunity includes both external and internal defenses. These defenses are always present in the body.

Adaptive immunity refers to antigen-specific immune response. The adaptive immune response is more complex than the innate. The antigen first must be processed and recognized. Once an antigen has been recognized, the adaptive immune system creates an army of immune cells specifically designed to attack that antigen. Adaptive immunity also includes a "memory" that makes future responses against a specific antigen more efficient.

Both Innate immunity and Adaptive immunity provide a defense against potential pathogens (disease-causing agents).


Cell-mediated immunity vs. Humoral immunity:

In the Cell-Mediated response, a macrophage eats a pathogen/antigen. The antigen is presented on the surface of the macrophage in a MHC class 2 receptor. A T-helper 1 cell with the corresponding antibody on its surface binds to the MHC class 2 receptor containing the antigen. The T-helper 1 cell then activates cytotoxic T cells. Cytotoxic T cells then patrol your body looking for other infected cells. Infected cells will have the antigen presented on the surface of the cell in a MHC class 1 receptor. When the cytotoxic T cell finds an infected cell, it will bind to the MHC class 1 receptor containing the antigen. The cytotoxic T cell will then release Interferon and Tumor Necrosis Factor. The former slows down the infected cell's reproduction, while the latter causes the cell to undergo apoptosis. The humoral system takes down pathogens floating in the blood, while the Cell-Mediated response kills cells that have become infected with the pathogen.

In Humoral immunity, B cells, which have antibodies attached to their surface, will then bind to an antigen floating around in the blood. Once this occurs, the antigen will be endocytosed and subsequently presented on the surface of the B cell in a MHC class 2 receptor. A T-Helper 2 cell containing the same antibody will bind to the MHC class 2 receptor on the B-cell. This will cause the B-cell to differentiate into plasma cells and memory B-cells. Plasma cells generate free floating antibodies, memory B-cells stay around in case of later infection.

Both the humoral and cell-mediated immune responses are directed at protecting the body from infection.


Process of the local inflammatory response:

Local inflammation occurs when bacteria enters a break in the skin. Inflammatory reaction is initiated by nonspecific mechanisms of phagocytosis and complement activation. As inflammation progresses, B cells produce antibodies against bacterial antigens. In an inflamed area, leukocytes attach to the surface of endothelial cells. Neutrophils arrive first in response to inflammation followed by monocytes, then the T cells, which then undergo extravasation.

Characteristics of local inflammation include the following
  • The tissues in the area are red and warm, as a result of the large amount of blood reaching the site.
  • The tissues in the area becomes swollen, again due to the increased amount of blood and proteins that are present.
  • The area is painful, due the expansion of tissues, causing mechanical pressure on nerve cells, and also due to the presence of pain mediators.

Inflammatory Response

Acute Inflammation

As our defense mechanism against illness and disease, our immune systems are the cornerstone to keeping us fit and healthy. Working in the medical field, you will need to know how the immune system is affected and what to do to protect yourself and the patients from illness and disease.


Human Physiology Tenth Edition Stuart Ira Fox
Human Physiology notes from chapter 15 on Immune System