γδ T cells:: novel initiators of adaptive immunity

In this review, we discuss the potential role of human gamma delta T cells in the control of adaptive immunity. Our latest findings emerged as a consequence of our working hypothesis, which predicts a close relationship between the migration control in leukocytes and their function in immune processes as diverse as hematopoiesis, initiation of adaptive immunity, and immune surveillance in peripheral tissues. Leukocyte migration control is defined by the combination of migration and adhesion receptors on their surface and the tissue distribution of the corresponding ligands. According to our hypothesis, leukocytes featuring migration receptors for homing to lymph nodes (LNs) will also display activities that preferentially take place within LNs. Following this line of thought, by showing LN-homing properties in a subset of human gamma delta T cells, we speculated that gamma delta T cells influence the initiation of T- and B-cell responses. Here, we summarize our recent data, showing that LN-homing gamma delta T cells have potent antigen-presenting cell characteristics. This unexpected finding is discussed with regards to microbial sensing by human gamma delta T cells and a possible role for these cells in anti-microbial immunity.