Simplify the following text for a Grade 13 native English-speaking person.
Original: After phagocytosis , macrophages and dendritic cells can also participate in antigen presentation , a process in which a phagocyte moves parts of the ingested material back to its surface .
Simplified: After phagocytosis , macrophages and dendritic cells can also do antigen presentation : this is when the phagocyte moves parts of the killed bacteria back to its surface .