The first is clonal deletion. Although it can be very effective, when actually studied in the periphery it seems to take a very long time to eliminate the autoreactive population [5]. In cases where

the antigen is chronic, this presents a problem since the animal continues to suffer a risk of autoimmunity while the cells are being “slowly deleted.” Therefore, two other processes are thought to operate to keep the cells in check — a functional inactivation, originally termed anergy and the action of Treg cells [6, 7]. However, a clear separation between the three processes in vivo and an understanding of the principles that CP-690550 datasheet lead to the choice of any one or a combination of them is still lacking. We have previously reported that adoptively transferring antigen specific T cells to mice expressing their target antigen resulted in the induction of anergy and “slow deletion”, but not of Treg cells [5]. Typically, these studies involved the infusion of 1–3 million TCR transgenic T cells to BGB324 concentration congenic hosts. About 10% of the injected cells effectively incorporate into the secondary lymphoid organs. Nevertheless, work from several labs (using acute immunization, not chronic or self-antigens)

subsequently suggested that at such high frequencies, the T-cell responses were severely constrained by interference between the transferred T cells themselves [8-14]. This phenomenon, termed clonal competition, affects the robustness of the initial T-cell response, the subsequent survival of the activated T cells (memory) and even the extent of differentiation into different subsets [13, 15]. We therefore wondered if such a “precursor frequency effect” could also influence the behavior of self-reactive T cells. Interestingly, we find that chronic antigen stimulation elicits a precursor frequency independent response pattern, compared to an acute challenge. In the latter case the expansion phase and to a much lesser extent, the

onset of contraction was influenced by how many T cells participated in the original response. However, the self-reactive T cells were only minimally affected by precursor frequency during the initial expansion phase. MYO10 Furthermore, in the later phase, recipients seeded with about a 100 self-reactive T cells showed no evidence of clonal deletion for over 4 months. But, even at lower frequency, the self-reactive T cells entered an anergic state marked by reduced recall cytokine production and no conversion to Foxp3 positivity. These data suggest that in the normal repertoire, T cells reactive to chronic self-antigens that escape thymic deletion can respond and persist in the periphery, albeit in an anergic state. The impact of initial precursor frequency on the magnitude of the subsequent T-cell response was modeled using an adoptive transfer strategy wherein log dilutions of congenically marked naïve T cells were injected intravenously into recipient mice and challenged in vivo.