Final answer:
A dendritic cell engulfs a pathogen through phagocytosis and then presents antigen fragments on its surface, signaling other immune cells to activate an immune response.
Step-by-step explanation:
When a dendritic cell detects a pathogen, it acts as an antigen-presenting cell (APC) within the adaptive immune response. The dendritic cell engulfs the pathogen via phagocytosis, digests it, and presents fragments of the antigen on its surface. These antigen fragments serve as signals to other immune cells, including T cells, which are then activated to mount a specific immune response against the pathogen. Dendritic cells do not secrete antibodies; instead, they present antigens to T cells, leading to the production of antibodies by B cells.