We thank James Huntington for providing the use of the Analyze-it program and David Straker for the English language editing of this manuscript. We are also very grateful to professors Pedro Paulo Xavier BMS-387032 cost Elsas and Maria Ignez Capella Gaspar for providing the transgenic mice used in this investigation. Conflict of interest statement: The authors declare

that there is no conflict of interest regarding the present work and the sponsors had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Funding support: This work was supported by the Brazilian the National Council of Scientific and Technological Development (CNPQ, Fellowships and Universal Grant 500992/2008-8) and by the Research

Foundation of the State of Rio de Janeiro (FAPERJ, Fellowships and Grants E-26/110305/2007, E-26/110132/2007, E-26/100416/2007, E-22/102733/2008) and a PIBIC CNPQ-UFRJ fellowship for undergraduate students. “
“Studies using protein have shown that the dose and duration of Ag exposure can influence a number of important parameters involved in T cell priming [1], [2], [3] and [4] including the acquisition of effector functions (e.g. Th1/Th2 phenotype) [5], [6] and [7], memory cell differentiation and the size of the memory cell pool [8] and [9]. Thus, the relationships between Ag dose and distribution, the number of pMHC complexes on an APC, costimulatory molecule interactions and pMHC/TcR stability determine the nature and extent of T cell activation and function. Epigenetic signaling pathway inhibitor Due to their non-replicative nature, DNA vaccines produce very low amounts of antigen in vivo (nanogram range), even when using the strongest viral promoters to drive Ag production [10]. However, despite the low amounts of Ag involved, and although primary immune responses can be difficult to demonstrate [11], recall

responses are often potent [11]. This may be related to the fact that, in contrast to other immunisation strategies where large bolus doses of Ag are administered, DNA vaccines are characterised by sustained production of small amounts of Ag [10]. Hence the links between pDNA distribution following injection, amount of Ag produced (and Ag persistence) and the identity and localisation of cells presenting DNA-encoded Ag may have important consequences next for both quantitative and qualitative aspects of T cell responses induced by DNA vaccines. However, the relationship between cells that acquire pDNA, and those expressing or presenting DNA-encoded Ag to naïve T cells is still unclear. Thus, in the context of intramuscular DNA vaccination it will be important to determine the distribution of cell-associated DNA; which cells produce and present antigen; where, when and how long they do this for; their phenotype and activation status and the relationship between these parameters and CD4+ T cell activation.