The First Line of Defense

Epithelial tissues cover the majority of the body’s external and internal surfaces, as well as its organs. These tissues will inevitably serve as the first line of defence against inorganic, organic, and microbial invaders. The main cell type in these tissues is epithelial cells. Aside from their role as a cellular barrier, there is growing evidence that epithelial cells play an important role as both initial sensors of danger and executors of appropriate defence responses. These cells perform a variety of critical functions in order to maintain tissue integrity in both health and disease. In this review, we look at some of the different innate immune functions of epithelial cells in mucosal tissues that are constantly exposed to a plethora of both harmless and pathogenic contaminants. We talk about how epithelial cells avoid ineffective immune responses.

First line of defense definition

A set of physical barriers between the inside of the body and the outside world is the first line of defence against any invasion of the human body. Skin, tears, and the stomach lining may not seem like very impressive defence systems until you consider what happens when they don’t work. Skin damage, such as burns or cuts, can quickly lead to complications and infections that, in the absence of modern antibiotics, could be fatal.

When the body’s outer line of defence is breached, it immediately launches its first major attack against the invading substances. This is known as innate immunity, and it is composed of a collection of white blood cells as well as groups of chemical messengers.

Innate immunity is triggered by the recognition of a set of molecules found only on invading substances rather than on body cells. An inflammatory response will be triggered by any sign of bacterial lipopolysaccharide, double-stranded RNA, or bacterial flagellin.

What is the immune system?

The immune system is critical to our survival. Without an immune system, our bodies would be vulnerable to bacteria, viruses, parasites, and other pathogens. 

This vast network of cells and tissues is constantly on the lookout for intruders, and when one is detected, a complex attack is launched.

The immune system is distributed throughout the body and consists of numerous types of cells, organs, proteins, and tissues. Most importantly, it can tell the difference between our tissue and foreign tissue — self and non-self. The immune system also recognises and eliminates dead and faulty cells.

When the immune system encounters a pathogen, such as a bacterium, virus, or parasite, it mounts an immune response. We’ll explain how this works later, but first, meet some of the main characters in the immune system.

What is a physical barrier?

The first line of defence is the innate immune system, which is divided into two categories: physical/chemical barriers and nonspecific resistance.

The aid in pathogen elimination and the prevention of tissue and/or blood infections. Furthermore, components secreted by the skin or mucosa, such as sweat, saliva, tears, and mucous, contribute to a basic barrier against invading pathogens.

The skin serves as an impermeable physical/mechanical barrier that keeps many pathogens out of the body. Similarly, mucosa or mucous membranes that line the immediate internal systems produce mucus, which aids in the trapping of pathogens. Hairs within the nasal cavity, as well as cerumen (earwax), trap pathogens and pollutants.

Some acidic fluids, such as gastric juice, urine, and vaginal secretions, kill pathogens by lowering the pH. Furthermore, lysozyme, which is found in tears, sweat, and saliva, acts as a critical antimicrobial agent in the destruction of pathogens.

Sensor functions of epithelial cells

Rapid detection of pathogens and other potentially dangerous incidents is critical for disease prevention. Rapid recognition allows for the timely initiation of an appropriate response to eliminate the threatening situations. Pathogen recognition, for example, is known to facilitate phagocytosis by binding and engulfing the pathogen. Additionally, signalling pathways activated by attacking pathogens or recognising danger are linked to lysosomal degradation pathways. However, epithelia are not only confronted with dangerous insults, but also with harmless microbes and innocuous contaminants on a daily basis. To avoid immunopathology, these sensory pathways must be tightly controlled.

Conclusion

Epithelial tissues cover the majority of the body’s external and internal surfaces, as well as its organs. A set of physical barriers between the inside of the body and the outside world is the first line of defence against any invasion of the human body. When the body’s outer line of defence is breached, it immediately launches its first major attack against the invading substances. This is known as innate immunity, and it is composed of a collection of white blood cells as well as groups of chemical messengers. Innate immunity is triggered by the recognition of a set of molecules found only on invading substances rather than on body cells. This vast network of cells and tissues is constantly on the lookout for intruders, and when one is detected, a complex attack is launched. The immune system is distributed throughout the body and consists of numerous types of cells, organs, proteins, and tissues. The first line of defence is the innate immune system, which is divided into two categories: physical/chemical barriers and nonspecific resistance.