Immune responses in the skin: Not so skinny at all

The immune system is our defence network and primarily geared to protect us from pathogens and tumors. This aspect is evident in people who lack or possess a compromised immune system and are, therefore, highly susceptible to infections and development of cancer, as in AIDS patients (Nandi et al. 2020). However, healthy humans possess commensals in the gut and have developed a symbiotic relationship with these microbes. Indeed, we benefit from gut microbes that reside within us due to the production of microbial products such as vitamins, short-chain fatty acids, and other metabolites. As the gut flora changes with disease, information on the changed microbiome can be highly reflective of our health status (Shreiner et al. 2015). Recently, efforts have been directed towards better understanding of host responses towards commensals. While it is true that most of these efforts have focused on the gut, other organs have also been studied such as the respiratory tract and oral cavities. Two new studies have shed light on immune responses in the skin (Bousbaine et al. 2024; Gribonika et al. 2024). Why the skin? In fact, the skin is the largest and most well-exposed organ harboring immune capabilities to deal with several commensals (Belkaid and Segre 2014; Honda et al. 2019; Zhang et al. 2022). Most importantly, bacteria obtained from the skin in healthy humans are coated with antibodies, demonstrating host-directed immune responses (Metze et al. 1991); also, immunodeficient people are susceptible to skin infections (Lehman 2014). However, a detailed understanding of the players involved, and the extent of skin-directed immune responses in dealing with various microbes are lacking. Two recent papers have shed new light on immune responses in the skin utilizing high end flow cytometry, several strains of mutant mice and RNA seq (Bousbaine et al. 2024; Gribonika et al. 2024).