CD4 and influenza: We studied the impact of IL-21 on monocyte subset distribution in light of recent reports linking CD11bhi-expressing monocytes with higher levels of inflammatory cytokine secretion, lower CD4+ T cell proliferation, diminished postvaccination influenza antibody titers, greater arterial thickness, and elevated plasma levels of CRP, LPS, and sCD14 in HIV-infected persons (18, 40, 52).