Innate Immune Barriers: Skin, Microbiome, and Interferons

Skin as a Barrier & Portal of Entry

Protective Functions of Skin

The skin serves as a primary physical barrier against infection, preventing the entry of pathogens into the body. However, if the skin is breached, it can also act as a portal of entry for infectious agents.

• Barrier properties:

  • Keratin toughens the skin, making it resistant to microbial invasion.

  • Dryness and acidity of the skin inhibit microbial growth, creating an inhospitable environment for many pathogens.

  • Constant cell renewal removes attached microbes, reducing the risk of colonization.

• Portal of entry:

  • Pathogens can enter through cuts or abrasions in the skin and spread to deeper tissues, potentially causing infection.

Microbiome as Innate Immune Barrier

Physical and Chemical Barriers

The normal microbiota, or microbiome, provides an additional layer of protection against pathogens through both physical and chemical mechanisms.

• Physical barrier:

  • Normal microbiota compete with pathogens for colonization sites and nutrients, limiting the ability of harmful microbes to establish themselves.

• Chemical barrier:

  • Microbiota produce antimicrobial peptides (such as bacteriocins) that inhibit the growth of pathogens.

Interferons

Role in Antiviral Defense

Interferons are signaling proteins produced by cells in response to viral infection. They play a crucial role in limiting the spread of viruses and activating immune responses.

• Production:

  • Interferons are synthesized by cells upon viral infection.

• Effects:

  • Interferons induce nearby cells to reduce transcription and translation, thereby inhibiting viral replication.

• Immune activation:

  • Interferons stimulate immune cells to target and destroy virus-infected cells, enhancing antiviral defense.

Example: Interferon alpha and beta are used therapeutically to treat certain viral infections and cancers.