My understanding is that when an APC (more specifically a dendritic cell) encounters an antigen in the periphery, it ingests it and presents it on its surface. It then migrates to lymph nodes to activate the T-cell that has the specific receptor for this antigen.
Now, I know that T-cells circulate throughout the body, but given the amount of the cells in a lymph node, and the fact that only a few T-cells are specific for a given antigen, it seems to me highly improbable for the APC to meet the specific T-cell.
Is it really that the APCs randomly check every T-cell there? If so, do we know how long would that take? Or is there a way to quickly locate the specific T-cell?