Final answer:
Dendritic cells present antigen to T cells to activate them and can be found in secondary lymphoid tissues.
Step-by-step explanation:
Dendritic cells function as antigen-presenting cells (APCs) and play a key role in activating T cells. They can be found in secondary lymphoid tissues such as lymph nodes. Dendritic cells have a complex repertoire of receptors that allow them to recognize a wide range of pathogens and present antigen to T cells, activating the immune response.