Recreating Human Skin In Vitro: Should the Microbiota Be Taken into Account?

Skin plays crucial roles in the human body: besides protecting the organism from external threats, it acts as a thermal regulator, is responsible for the sense of touch, hosts microbial communities (the skin microbiota) involved in preventing the invasion of foreign pathogens, contains immunocompetent cells that maintain a healthy immunogenic/tolerogenic balance, and is a suitable route for drug administration. In the skin, four defense levels can be identified: besides the physical, chemical, and immune barriers that are inherent to the tissue, the skin microbiota (i.e., the numerous microorganisms living on the skin surface) provides an additional barrier. Studying the skin barrier function or the effects of drugs or cosmetic agents on human skin is a difficult task since snapshot evidence can only be obtained using bioptic samples where dynamic processes cannot properly be followed. To overcome these limitations, many different in vitro models of human skin have been developed that are characterized by diverse levels of complexity in terms of chemical, structural, and cellular composition. The aim of this review is to summarize and discuss the advantages and disadvantages of the different human skin models so far available and to underline how the insertion of a proper microbiota would positively impact an in vitro human skin model in an attempt to better mimic conditions in vivo.

1954-2024: 70 years of histochemical research with the European Journal of Histochemistry.

This Editorial celebrates the 70th anniversary of the European Journal of Histochemistry since its foundation as Rivista di Istochimica Normale e Patologica, and introduces a Special Collection of selected articles on the application of the histochemical approach for investigating cell biological features and processes in animals and plants, and under diseased conditions. The year 2024 is a special one for histochemists, as 100 years ago J.W. Robert Feulgen and H. Rossenbeck introduced the histochemical procedure for the specific stoichiometric staining of DNA in histological samples: to commemorate this influential publication, three papers in the present issue are devoted to the application of the Feulgen reaction at light and electron microscopy, and in cytometry.