However, it is also notable that the inhibitory effect of DN T cells in an antigen-specific setting is superior to non-specific inhibition. As a result of the vigorous HBeAg-specific proliferative
property of the DN T-cell population during in vitro culture, it is possible CP-690550 chemical structure that the DN cells are derived from HBeAg-specific CD4+, CD8+ or from an independent DN progenitor population. To determine the origin of the DN T-cell population, depletion of T-cell subpopulations from total spleen of HBeAg × 7/16-5 dbl-Tg mice was performed and the remaining cells were cultured in vitro with p120–140 for 4 days and compared with total spleen cells. As shown in Fig. 6, CD4+ and CD8+ T-cell depletion from total spleen did not affect the generation of the DN T-cell population in the culture (i.e. 40–48%). However, negative depletion of DN T cells before culture prevented the generation of the HBeAg-specific DN T-cell population in the 4-day culture (i.e. 8%). Hence, HBeAg-specific DN T cells exist in the periphery and are not generated from CD4+ or CD8+ T cells in the periphery. It is notable that without DN T cells, CD4+ T cells from HBeAg × 7/16-5 dbl-Tg mice demonstrate robust proliferation GW-572016 molecular weight and cytokine
production in vitro (data not shown). The frequency of Vβ11+ DN T cells in thymus and spleen ex vivo was measured. The Vβ11+ DN T cells in thymus of 7/16-5 × HBeAg dbl-Tg mice were present at a slightly higher frequency (5% higher) than in the thymus of 7/16-5 × HBcAg dbl-Tg mice. There was also a 20% higher frequency of Vβ11+ DN T cells in
the ex vivo spleens of 7/16-5 × HBeAg compared with the spleens of 7/16-5 single TCR-Tg mice (data not shown). However, in absolute terms DN Vβ11+ T cells are present in low frequency in situ in HBeAg × 7/16-5 dbl-Tg mice (i.e. 3–5%) and require antigen stimulation for expansion. It is not clear if DN T cells can proliferate and be activated in vivo. To determine the capability of DN T cells to expand in vivo, we injected HBeAg-derived p120–140 (250 μg) into 7/16-5 × HBeAg-dbl Tg mice. As shown in Fig. 7, at least a twofold increase in the DN T-cell frequency in vivo was observed 1 and 2 weeks after injection, whereas in control, 7/16-5 mice no evidence of expansion of DN T cells occurred. Although HBeAg-specific Treg cells appear quiescent in vivo HDAC inhibitor in HBeAg × 7/16-5 dbl-Tg mice, these cells are capable of being activated in vivo, in this case by exogenous antigen. The ability to activate DN T cells in vivo will permit further studies of their in vivo function. To further pursue the origins of DN T cells, we bred 7/16-5 × HBeAg dbl-Tg mice onto MHC class I KO, and TCR α-chain KO backgrounds. Because the 7/16-5 TCR is surprisingly expressed on CD8+ as well as CD4+ T cells in the thymus and the periphery, it was important to determine if expression of CD8 was necessary for selection of the DN T-cell population.