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By analyzing the entry of primary and memory cells into the cell cycle, we found that the two populations proliferated similarly until day 5; after this time, fewer of the reactivated memory cells proliferated. At this time, fewer of the reactivated memory cells made IL-2 than primary responding cells, but more made IFN\u03b3. Both these factors affected the low proliferation of the memory cells, because either exogenous IL-2 or inhibition of IFN\u03b3 increased the proliferation of the memory cells.<\/jats:p>","DOI":"10.1073\/pnas.0807449105","type":"journal-article","created":{"date-parts":[[2008,9,11]],"date-time":"2008-09-11T21:10:06Z","timestamp":1221167406000},"page":"14521-14526","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":51,"title":["CD4 memory T cells divide poorly in response to antigen because of their cytokine profile"],"prefix":"10.1073","volume":"105","author":[{"given":"Megan K. 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