ABSTRACT
Dendritic cells (DC) are powerful inducers of primary T-cell responses, but their role in secondary responses has not been extensively analysed. Here, we address the role of two DC subsets derived from human CD16(+) (16(+) mDC) or CD16(-) (16(-) mDC) monocytes on the reactivation of memory responses. CD4(+) CD45RA(-) memory T cells were obtained from adult blood donors, and central (T(CM)) and effector (T(EM)) memory T cells were isolated by fluorescence-activated cell sorting with anti-CCR7 antibodies. The 16(+) mDC and 16(-) mDC were cocultured with autologous lymphocytes, either unpulsed or loaded with purified protein derivatives of Mycobacterium tuberculosis (PPD) or tetanus toxoid (TT), and were analysed for up to 8 days. Over a range of doses, 16(+) mDC drove stronger T-cell proliferative responses against both antigens. Overall, antigen-specific memory cells tended to acquire a phenotype of T(EM) at later time-points in the culture, whereas cells that had completed fewer cycles of division were similar to T(CM). The 16(+) mDC induced higher rates of proliferation on both T(CM) and T(EM) lymphocytes than 16(-) mDC. This phenomenon was not related to the ability of both DC to induce CD25 expression on T cells, to lower secretion of interleukin-2, or to raise production of interleukin-10 during T-cell/16(-) mDC cocultures. The induction of T(CM) effector capacity in terms of interferon-gamma production was faster and more pronounced with 16(+) mDC, whereas both DC had similar abilities with T(EM). In conclusion, these data might reveal new potentials in vaccination protocols with 16(+) mDC aimed at inducing strong responses on central memory T cells.
