Immunology and Serology Topic: Immunity - labsstudies

Immunology and Serology Topic: Immunity

Immunology and Serology Topic: Immunity

Definition of Immunity 

Immunity is defined as the ability of the body to protect itself from pathogenic microorganisms and provide a defense against their harmful effects.
There are two types of immunity:

  1. Non-specific immunity
  2. Specific Immunity

1. Nonspecific (natural or innate) immunity

Non-specific immunity, also known as natural or innate immunity, is the first line of defense against any infectious agent. Nonspecific host responses provide an effective barrier that prevents microorganisms from penetrating, inhibits or destroys the invader if it gains access to the tissues, and eliminates or neutralizes any toxic substance produced by the infectious agent.

In the immunocompetent host, several mechanisms are available. Physical or mechanical barriers, biochemical factors, cellular mechanisms, the role of normal flora, and inflammatory reactions are examples of these.

Physical or mechanical impediment
The intact skin and mucus membrane serve as effective mechanical barriers against infectious agents. Because of low moisture, low pH, and the presence of secreted inhibitory substance, the skin’s surface also inhibits the growth of most microorganisms. Some microorganisms, however, can enter the skin through hair follicles, sebaceous glands, or sweet glands.

Mucus membranes, like epithelial layers, have an underlying connective tissue layer. They are found throughout the digestive, respiratory, urinary, and reproductive tracts. For example, mucous production and ciliary movement protect the epithelial surface that lines the nasal cavity and throat. Microorganisms adhere to mucous due to its viscosity. The mucus layer is constantly moved to the mouth by epithelial cells with cilia, where it is swallowed and eliminated along with the trapped microorganism.

Furthermore, coughing removes microorganism-containing mucus. Most microorganisms are washed away in the urethra by the rapid flow of urine. Tears that clean the conjunctiva serve a similar defensive purpose.

Interferons are small proteins that eukaryotic cells produce in response to viral infection. For a few hours, even a day, the virally infected cell produces interferon, which is excreted and used by other cells. When these cells become infected with the same or a different virus, the interferons cause the cells to produce molecules that prevent the infecting virus from replicating.

Mechanism of the cell
Neutrophils and natural killers, as well as alveolar macrophages, remove particles and organisms that enter the alveoli.
Neutrophils are the first phagocytes in an infected area and can phagocytize some microbes non-specifically. Natural killer cells are large lymphocytes that kill unwanted cells such as tumor cells and virus-infected cells.

Normal flora’s role
The human body is inhabited by a large number of microorganisms, primarily bacteria, collectively known as the body’s normal flora or commensals. The term “normal flora” implies that such microbial inhabitants are harmless. Normal flora microorganisms do not, for the most part, cause disease.
The commensal can inhibit the growth of potentially pathogenic organisms by occupying attachment sites and producing anti-pathogenic substances.
They also compete for vital nutrients for growth.

Inflammatory responses
The inflammatory response is the body’s vascular and cellular response to invading microorganisms or injury.
It is a powerful defense mechanism in humans and other animals. Inflammation has five stages: Initiation (tissue damage), Tissue response, Leukocyte response, Tissue repair (resolution), and Cure.

Damaged cells at the site of injury initiate the tissue response by releasing chemical factors such as histamine, which causes vasodilatation and increased capillary permeability, allowing fluids and blood cells to enter the site. The leukocyte response is then completed by phagocytic cells engulfing the microbes and damaged tissue.
The inflammatory response, in addition to destroying and removing an injurious agent such as a microbe or its products, limits the effects of the agent or its products by confining or walling it off from the surrounding tissues.

This is because blood clots around the site keep the microbe or its products from spreading to other parts of the body. Tissue repair is the final stage of inflammation, after all harmful agents or substances have been removed or neutralized at the injury site. The ability of a tissue to repair itself is determined by the tissue involved. Skin, as a simple tissue, has a high capacity for regeneration. However, nerve tissue in the brain does not appear to regenerate.

2. Specific immunity

The specific immune response, also known as acquired or adaptive immunity, is a defense system that protects the body from pathogenic microorganisms and other types of disease such as cancer It enables the body to recognize, remember, and recall. and react to a specific stimulus, an antigen Specific Immunity can result in the elimination of microorganisms and in disease  recovery, and it frequently leaves the host with specific immunologic memory.

Acquired resistance is a memory or recall condition that allows the host to respond more effectively if reinfection with the same microorganism occurs. As a result of such acquired immunity, we usually only get sick from a single disease, such as measles.

Specific immunity can be active or passive, and each type can be acquired naturally or artificially.

Passive immunity

It is a type of immunity in which antibodies produced elsewhere are given to the individual. They are divided into two groups:

  • Naturally acquired passive immunity: antibodies transferred from mother to fetus across the placenta and to the newborn in colostrums and breast milk during the first few months of life.
  • Artificially acquired passive immunity: the introduction of antibodies produced by an animal or a human into an individual in order to prevent or treat infection.

Active immunity

It is produced by the individual’s immune system in response to a foreign antigen.

  • Naturally acquired active immunity: This is immunity derived from infections encountered in daily life.
  •  Artificially acquired active immunity: It is stimulated by initial exposure to specific foreign macromolecules through the use of vaccines to artificially establish a state of immunity.

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