Posted: February 1st, 2023

Skin: An Element of Innate Immunity Paper

Skin is the outer covering of the body. It is the largest organ of our body and provides us with a sense of touch. It protects the internal structure from harmful radiation (UV) from the sun, against pathogens and chemicals. It serves as a physical barrier and is associated with the innate immunity of the body. In humans, the skin is composed of two types of layers: epidermis and dermis.

The epidermis is the outer layer of the skin that is in contact with the environment. It contains cells called keratinocytes. Keratinocytes constitute 95% of the epidermis. They act together with epithelial cells and neutrophils and create small amphipathic and cationic molecules known as antimicrobial peptides (AMPs). AMPs acts as the first line of defense for a microbial pathogen. The epidermis also contains several antigen-presenting cells known as Langerhans cells. These cells get activated on encountering a microbial antigen. The function of these cells is to present antigens to the other cells of the immune system.

Epidermis also has some cells of adaptive immunity (T cells) present in it. These cells are activated as a result of the components secreted by the elements of innate immunity like interleukins. This provides a connection between innate and adaptive immunity.

The dermis is the inner layer of skin. It is composed of connective tissues, blood vessels, and various cell types. It provides elasticity and tensile strength to the skin. The basement membrane provides a connection between the epidermis and dermis. The dermis contains mast cells. TC (tryptase positive, chymase positive) type mast cells are present in the dermis. Tryptase degrades the extracellular matrix by working on fibronectin. It allows the immune cells like lymphocytes, neutrophils to invade the epidermis to kill the foreign cell.

Skin also harbors a wide variety of microorganisms that is the native microflora of the body. The cells of the native microflora compete with foreign antigen for space and nutrition. It helps in lowering the attack and colonization of the foreign microbe on the skin.

The skin contains hair on it. The hair’s glands called sebaceous glands are associated. These glands secrete an oily or waxy matter known as sebum on the skin. It lubricates the hair and the skin and prevents the attachment of a pathogenic microbe.

The acidic pH. and dry conditions on the skin also help in preventing the attack of the foreign pathogen as it doesn’t provide an optimum condition for a microbe to colonize and grow.