Traditionally, naive and memory cells are characterized ex vivo by their mutually exclusive expression of CD45RA and CD45RO molecules, respectively. However, it is known that upon activation and proliferation in vitro naive T lymphocytes first acquire the expression of CD45RO and subsequently lose the expression of CD45RA, making the timing of the analysis of CD45 molecule expression in vitro critically important [23]. Nevertheless, it can be assumed that the percentage of CD4+CFSElow cells with the CD45RA-CD45RO+ phenotype also reflects

more or less accurately the frequency of memory cell-derived antigen-specific precursor T cells in our experimental system. Therefore, based on our data it this website seems that in children with CD CD4+ T cells specific to gTG have mainly a memory phenotype, whereas Pifithrin-�� in vitro in healthy children these cells are more predominantly of naive origin. Consequently, in children with CD the stronger proliferative responses observed to gTG also presumably reflect the higher

frequency of memory CD4+ T cells specific to gTG in vivo. We also examined the expression of the gut-homing β7 integrin and observed that gTG-specific T cells expressed high levels of the molecule. This finding suggests that the CD4+ T cells specific to gTG are generated in the gut mucosa and are capable of trafficking back to the intestine. The specificity of the increased β7 integrin expression by gTG-specific T cells was demonstrated by a considerably lower expression of the molecule by TT-specific T cells that are primed by subcutaneous injections and thus lack the capacity to traffic to the gut. Our current results corroborate earlier reports demonstrating the

expression of β7 integrin by CD4+ T cells specific to gTG [12,14]. In conclusion, we have shown that CD4+ T cells specific to gTG are detectable in the peripheral blood of more than half of children with newly diagnosed CD, whereas this was significantly less common among Clomifene healthy control children. In contrast, the responses to native gliadin did not differ between children with CD and healthy controls. We also demonstrate that in children with CD the CD4+ T cells specific to gTG have a memory cell phenotype and express β7 integrin as a marker of gut homing. Taken together, our results support the widely accepted model for the importance of T cell responses to gTG epitopes in the pathogenesis of CD. Moreover, further development of assays to detect specific CD4+ T cell responses to gTG in the peripheral blood may also have practical applications for the diagnostics of the disease, as demonstrated recently by HLA-tetramer staining in patients with uncertain CD [24]. We thank Virpi Fisk for the skilful technical assistance. The study was supported financially by the Finnish Cultural Foundation, the Finnish Coeliac Society and the Finnish Medical Foundation. The authors confirm that there are no conflicts of interest.