Mechanisms by which chronic ethanol consumption impairs cutaneous immunity

The immunosuppressive effects of chronic alcohol abuse are profound, wide-ranging and readily apparent at the body's barriers. In the skin, alcoholism is associated with an increased incidence and severity of infection; yet the precise immunologic alterations responsible remain poorly understood. Cutaneous homeostasis and immunity are afforded via coordinated efforts of tissue-specific immune cell networks. Here, the Meadows-Cook murine model of alcoholism was used to investigate the impact of chronic ethanol (EtOH) exposure upon the following: 1) the composition and function of skin-resident dendritic cells (DCs) and T cells in preimmune mice 2) infection outcome and host defense following Staphylococcus aureus skin infection 3) the induction of cutaneous oxidative stress

Chronic EtOH feeding caused a baseline reduction in skin DCs and T cells with the most pronounced effects occurring in self-renewing compartments (i.e, Langerhans cells and γδ T cells). In addition, we found that EtOH-induced immune cell subset loss was often associated with dysfunction of the remaining population. For DCs, EtOH-induced hyporesponsiveness was observed in both in vitro and in vivo migration assays. Defects in the former system could be corrected via TNFα restoration. EtOH-induced dysfunction in skin T cells was evident by the decreased upregulation of JAML and diminished production of IL-17 by epidermal and dermal γδ T cells respectively. In a murine model of EtOH withdrawal, some but not all of the EtOH-induced defects occurring in skin DCs and T cells recovered after cessation of EtOH exposure.

Prior to this work, the impact of chronic EtOH exposure upon the cutaneous immune system had not been investigated in a murine model of infection. Using a novel method of cutaneous S. aureus challenge, evidence of exacerbated staphylococcal disease in EtOH-fed mice included skin lesions that were larger and contained more organisms, greater weight loss and increased bacterial dissemination. Infected EtOH-fed mice demonstrated poor maintenance and induction of PMN responses in the skin and draining LNs respectively. Additionally, altered PMN dynamics in the skin of these mice corresponded with reduced production of IL-23 and IL-1β by CD11b+ myeloid cells and IL-17 production by γδ T cells, with the latter defect occurring in the draining LNs as well. In addition, IL-17 restoration via intradermal injection improved bacterial clearance defects in EtOH-fed mice. Taken together, these findings show that the EtOH-induced increase in S. aureus-related injury/illness (i.e., weight loss, bacterial burden, lesion size) corresponds with defects in the IL-23/IL-17 inflammatory axis and poor PMN accumulation at the site of infection and draining LNs.

Finally, two complementary tools (mice deficient in molecules that promote or inhibit reactive oxygen species induction) were used to investigate the role of oxidative stress as a driver of cutaneous immune dysfunction. In these studies intriguing evidence was obtained indicating that some but not all of the mechanisms by which oxidative stress contributes to cutaneous immune dysfunction are initiated through the Thurman cascade. In conclusion, this report offers new information about the impact of EtOH on cutaneous host defense pathways and provides potential mechanisms of explaining why alcoholics are predisposed to severe skin infections.