It was this second wave of pMHC+ cells that was essential for full CD4+ T cell differentiation and effector function. We observed very similar kinetics using our EαGFP fusion protein, to that reported

previously and following the initial appearance of GFP+ and Y-Ae+ cells in the draining LNs at 1–4 h, these cells decreased until 12–24 h when a second wave of migrants arrived this website from the injection site. By 24 h we observed large numbers of Y-Ae+ cells, although they showed considerable heterogeneity with respect to both GFP and CD11c expression. This may reflect different states of maturation and/or different cell lineages (e.g. myeloid DC vs. pDC). Although we observed Y-Ae+ and GFP+ cells in non-draining LNs (data not shown), the low frequency of these cells highlights how Ag distribution and thus effective Ag dose, has important consequences for the location and/or duration of Ag presentation. Similarly, when we immunised with different Ag doses we observed rapid diminution of our ability to detect

cell-associated Ag and pMHC complexes with decreasing Ag dose. Ag doses lower Bcr-Abl inhibitor than 100 μg substantially decreased our ability to detect GFP+ or Y-Ae+ cells within both the CD11c+ and CD11clow/− populations, however we were confident that we could detect cells from these unpurified cell suspensions down to a dose of 1 μg–100 ng. Selective enrichment of

Y-Ae+ cells may further improve the sensitivity of these analyses. Collectively, our results using EαGFP (and EαRFP) protein, highlight the impact of Ag dose and distribution and importance of detailed kinetic analyses for detecting rare pMHC cells in vivo. Nevertheless, we did detect rare pMHC+CD11c+ cells in the peripheral LNs of pDNA-immunised mice, 3 days after injection. In contrast to the clearly defined, although heterogeneous, Y-Ae+ cells we observed 24 h after protein injection, we did not many observe a discrete population of pMHChigh cells, but rather an increase in Y-Ae fluorescence intensity of about 14% of CD11c+ cells. This was similar to what we observed 72 h after protein immunisation, when Ag was limiting. We were unable to demonstrate CD11c+pMHC+ cells in tissue sections, which was not particularly surprising as we observed only a slight increase in fluorescence intensity by flow cytometry. However, we observed dispersed Y-Aehigh cells in the subcapsular sinus of draining LNs, 3 days after injection of Eα-expressing plasmids. Due to the scarcity of these cells we were unable to phenotype them further, but their location in the subcapsular sinus suggests they had migrated to the LNs in afferent lymphatics or were subcapsular sinus resident macrophages [45] and [46].