Immune disorders with cutaneous manifestations: exploration of genetic and immunological bases

The skin functions as a barrier against invasion of pathogens from the environment. This function is fulfilled by first, rich variety of microflora being housed on the skin to outcompete potential harmful microbes in the environment for survival; second, the complex structural architecture of the skin, e.g. the stratified nature of outer epidermis and inner dermis, presence of tight junctions, etc; and third, the constant presence of competent immune cells to effectively clear infections. However, in situations such as observed in genetically pre-disposed individuals, the skin barrier can be breached leading to recurrent or chronic susceptibility to infections like S. aureus and candida. Other cutaneous disorders like pruritus, vitiligo, psoriasis, and keratosis, etc have been observed. Usually, no treatment regimens exist for patients except for targeted treatment of recurring infections or bone marrow/stem cell transplantation. Such treatments have drawbacks such as development of resistant strains or graft versus host disease (GVHD) respectively. Understanding the molecular mechanism underlying the pathophysiology of such disorders is key to designing therapeutic interventions. This study focused on understanding the genetic and immunological defects underlying two different immune disorders with cutaneous manifestations. First, we sought to understand the transcriptional mechanism Aire (autoimmune regulator) uses to regulate the gene expression of pancreatic-specific antigens in the thymic medulla in promoting tolerance towards the antigens. The Â#Hierarchical modelÂ# of gene regulation was tested in a thymus, in a situation whereby Aire adopts peripheral Pdx1 gene regulation mechanism. This mechanism allows thymic expression of pancreatic TRAs such as insulin (Ins2) and Sst in order to promote tolerance to these antigens. Gene expression analysis revealed that although thymic gene expression of Pdx1, Ins2 and Sst are Aire-dependent, Ins2 and Sst thymic gene expression could proceed in the absence of Pdx1. When tolerance towards insulin was monitored using insHEL transgenic system, our data showed no difference in the amount of tolerogenic insHEL-specific 3A9 TCR cells in Pdx1-deficient and Pdx1-sufficient thymic environment. These results suggest that although Aire drives the thymic expression of the transcription factor Pdx1 and its downstream autoantigens such as insulin, the thymic Pdx1 expression is not necessary for tolerogenic insulin expression in the thymus, thus, Aire does not use the Pdx1-dependent peripheral regulation pathways in the thymus. Our data supports a model for direct transcriptional activity on Aire-regulated genes in the thymus. Secondly, we focused on exploring the genetic and immunological bases of a case study patient clinically diagnosed with OS. Exome sequencing data revealed novel Gly573Ala mutation with potential damaging effect to the TRPV3 protein. This identification verifies and re-enforces the establishment of mutation in TRPV3 as the underlying genetic defect in OS. Additionally, a look at the immune profile resulted in the identification of immune dysregulation in the OS patient, particularly, hyper IgE, eosinophilia and high levels of Tfh cells. The immune dysregulation could be the primary defect with cutaneous manifestation of hyperkeratosis lesions. It could also be a secondary consequence of a primary cutaneous defect. Our data uncover the need for further investigation to 1) determine the penetrance of the immune dysregulation in other OS cases, 2) ascertain the pathophysiological mechanism of the immune dysregulation. In conclusion, the present study provides insights into the molecular mechanism of two immune disorders that present with cutaneous defects. In the case of APS1, our data supported the idea that the transcriptional regulatory mechanism of Aire is via direct targeting of Aire-dependent TRAs, although Â#hierarchicalÂ# transcription seemed plausible. This suggests that future studies should be geared toward a direct transcriptional mechanism by Aire. On the other hand, alternative approach to testing #hierarchical# model should consider TFs other than the known peripheral TFs that regulate the TRAs. In the OS study, the identification of novel Gly573Ala mutation contributes to the knowledge of clinical variants of TRPV3 which could be placed in database curated for clinical variants. More so, data on the detailed immune profile and immune dysregulation in a case of OS is the first to be reported. Our data, thus, sets the grounds for further studies regarding immunological component of OS pathophysiology.status: publishe