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What’s Important

  • The skin provides the first line of defense against external pathogens through a physical, chemical, and antimicrobial barrier maintained by the epidermis and the cutaneous microbiome.

  • In addition to barrier function, the skin acts as an innate immune sentinel, with Toll-like receptors responding to external pathogens and cellular damage to activate the local immune response.

  • Cytokines and growth factors released upon activation of innate immune signaling regulate local inflammation and function of resident skin cells. Growth factors specifically play an important role in regulating epidermal proliferation and synthesis of the dermal matrix.

  • Aging of the skin is associated with a decline in barrier function and increased activation of the innate immune system. These changes contribute to altered growth factor and MMP signaling which impair maintenance of the dermal matrix.

What’s New

  • Advances in sequencing technology have allowed increased insight into the diversity of the cutaneous microbiome. The balance of bacterial species and strains in each body site plays a role in regulating immune function.

  • Induction of innate immune signaling through activation of Toll-like receptors as part of a damage response plays an important role in regeneration and wound healing.

  • Anti-aging treatments targeted at modulating innate immune signaling have shown benefit for improving photoaging phenotypes.

What’s Coming

  • Therapy aimed at restoration of the skin barrier will clarify the role of skin barrier changes in initiating skin and systemic aging changes.

  • Better characterization of the cutaneous microbiome will facilitate understanding of shifts associated with aging to offer more targeted probiotic therapy for cutaneous aging.

  • Increased understanding of the role of the innate immune system in injury-mediated regeneration will offer new targets for promoting rejuvenation.

Little is known about the relationship between immunology and skin appearance; however, it is certain that the immune system plays an important role in the health of the skin and evidence is accumulating to indicate that the immune response plays a role in skin aging phenotypes. Work is ongoing to elucidate how this vital system interacts with the largest organ of the body. It is very likely that this segment of research, as it pertains to cosmetic dermatology, will offer significant potential for discovery of new therapeutics and procedures. This chapter will serve as a brief introduction to the skin as an immune organ and how the immune response plays a role in cutaneous aging.

In the past, the skin was viewed primarily as a physical barrier to prevent invading pathogens and other environmental toxins, including UV radiation, from penetrating into internal organs. However, we now know that the skin acts as an immense and integral immune organ and first point of contact with the environment, capable of initiating an intricate series of events leading to host defense. A basic review of skin immunology, including the role of antimicrobial peptides and lipids, the microbiome, cytokines and growth factors, will be provided as an important part of this discussion. Mechanisms ...

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