Functions of the skin microbiota in health and disease

Abstract

The skin, the human body's largest organ, is home to a diverse and complex variety of innate and adaptive immune functions. Despite this potent immune system present at the cutaneous barrier, the skin encourages colonization by microorganisms. Characterization these microbial communities has enhanced our knowledge of the ecology of organisms present in normal skin; furthermore, studies have begun to bring to light the intimate relationships shared between host and resident microbes. In particular, it is apparent that just as host immunological factors and behaviors shape the composition of these communities, microbes present on the skin greatly impact the functions of human immunity. Thus, today the skin immune system should be considered a collective mixture of elements from the host and microbes acting in a mutualistic relationship. In this article we will review recent findings of the interactions of skin microbial communities with host immunity, and discuss the role that dysbiosis of these communities plays in diseases of the skin.

Keywords: Antimicrobial peptides; Dysbiosis; Keratinocyte; Propionibacterium acnes; Staphylococcus.

Fig. 1

Diversity of the skin at different body sites. The physical and chemical features of the skin are not uniform across the body; rather, different anatomical locations show vast diversity in organization and the distribution of appendages and glandular structures. Shown are representative illustrations of the three major categories of skin environments.

Fig. 2

Diversity of the microbial communities populating the skin. (A) Microbial communities inhabiting the skin are extremely diverse, more so than those residing at other epithelial surfaces of the body. (B) In addition, communities residing on the skin at different anatomical locations differ greatly in their compositions. Reprinted from Refs.[4,7] with permission from Nature Publishing Group.

Fig. 3

Functional associations with microbial communities on the skin. Microbial communities on the skin contribute to host immune defense through a variety of mechanisms, as illustrated here.

Fig. 4

Models of dysbiosis of skin-resident microbes. Dysbiosis of skin-resident microbes has been associated with a variety of dermatological pathologies; however, it remains unclear whether alterations in microbial communities or intrinsic features of the host initiate these processes.