Macrophages　are　involved　in　a　number　of　diseases,　such　as　HIV　infection/AIDS,　tuberculosis,　tumor　development　and　atherosclerosis.　Macrophages　possess　several　cell　surface　receptors　(e.g.,　the　mannose　receptor,　MR)　that　may　serve　as　drug　delivery　cellular　portals　for　nanocarriers　(NCs).　In　this　study,　the　optimal　structural　configuration　for　cell　uptake　of　mannosylated　poly(ethylene　glycol)-conjugate　type　NCs　was　determined.　A　series　of　NCs　were　synthesized　to　systematically　evaluate　the　effects　of　the　number　of　mannose　units　(Man),　the　PEG　carrier　size　and　the　mPEG　spacer　length　between　adjacent　mannose　units　on　NC　uptake　into　MR-expressing　J774.E　murine　macrophage-like　cells.　Among　NCs　with　0,　1,　2　or　4　units　of　mannose,　the　uptake　of　(Man)(2)-NC　was　the　highest,　suggesting　a　trade-off　between　avidity　and　NC-MR　clustering　on　the　cell　surface　that　sterically　hinders　endocytosis.　This　optimal　(Man)　2-NC　configuration　was　built　into　subsequent　NCs　to　optimize　the　other　two　parameters,　PEG　carrier　size　and　spacer　length.　NCs　with　0,　5,　12,　20,　30　or　40　kDa　linear　PEG　carriers　showed　an　inverse　relationship　between　PEG　size　and　uptake.　The　12　kDa　PEG　carrier　was　chosen　for　investigating　the　third　parameter,　the　Man-Man　distance,　since　it　may　represent　the　best　trade　off　(i.e.,　tissue　penetration　vs.　systemic　clearance)　for　in　vivo　macrophage　targeting.　Three　(Man)(2)-PEG(12kDa)　NCs　with　different　Man-Man　distances　(39,　56　or　89　angstrom)　were　synthesized.　The　uptake　of　the　NC　with　the　56　angstrom　distance　between　mannoses　was　four-and　two-fold　higher　than　NCs　with　39　angstrom　and　89　angstrom　distances,　respectively.　Confocal　microscopy　confirmed　that　the　optimized　(Man)(2)-PEG(12kDa)　NC　with　the　56　angstrom　Man-Man　distance　was　internalized　via　endocytosis　consistent　with　temperature-dependent　active　uptake.　In　conclusion,　the　optimal　NC　structural　parameters　for　targeting　the　MR　on　macrophage-like　J774.E　cells　are　(i)　a　small　PEG　polymer　carrier,　(ii)　two　mannose　units　per　NC　and　(iii)　a　56　angstrom　distance　between　adjacent　mannose　units.　(C)　2014　Elsevier　B.V.　All　rights　reserved.