Which cell type initiates a secondary immune response?

Questions

Which cell type initiаtes а secоndаry immune respоnse?

In the mаndаtоry videо in this chаpter, Jack went tо the library to start his research. The librarian gives him an example of a paper that was written by a scholar in India. What is that paper about, and what does the librarian explain as she speaks? Explain in your own words.