Value of cell studies that reflect the natural situation and whether, histiocyte-derived U-937 cells are the cell-line of choice, for studies of HIV infection interactions of monocytes and macrophages
Garry Lynch, University of Sydney
27 October 2011
In the article by Ferrucci et al `Cellular phenotype impacts human immunodeficiency virus type 1 viral protein R subcellular localization¿ Virology Journal 8: 397 (10th of August) 2011 (1), applauded is their approach taken in this study of HIV Vpr protein localization, using cells that more closely represent the types of cells infected in nature as compared to numerous previous studies that deployed laboratory cell-lines (e.g., HeLa cells) derived from cell types that do not naturally harbour HIV infection. The latter approach has undoubtedly been useful and beneficial in many different situations to reveal various important aspects of HIV infection and its interactions. However, given the inherent and specialised compositions and proteome(s) of each different cell type that underpins their size, shapes and activities in the complex body system it is reasonable and pertinent to consider whether for other situations red herring or un-natural blind-ends similarly may have also been collaterally promulgated. And some for which we may still remain in the dark of their true biologic activities in their natural cell environment? Perhaps some of the differences in the HIV Vpr localisation (viz cytoplasmic versus nuclear) between cell types that are representative of naturally infected cells (this present study) versus laboratory manipulated cell targets may have uncovered one such instance.
Accepting the limitations of cell-lines as stand-ins for primary cells such as fresh PBMC¿s, raised is the question of whether U-937 cells is the ideal cell-line choice to in-general and collectively represent native monocytes and differentiated macrophages for HIV studies. As it is well known that there are significant differences in the HIV infection of monocytes and their more differentiated macrophage forms (2), it is unreasonable to lump them together as synonymous entities, and although related should be separately demarcated as monocytes and macrophages. U-937 cells were originally derived and developed from a case of histiocytic lymphoma (3). As such histiocytes (ergo U-937 cells) from bone marrow derived myeloid progenitors (4), differ from monocytes, as they are already well differentiated, and committed resident cells of connective tissue and are relatively inactive and immobile compared with other monocytes/macrophages. Furthermore as U-937 cells express cell surface markers that differ from primary monocytes (5, 6), they poorly represent monocytes. Perhaps a follow up study by these investigators is necessary to establish whether the localisation of Vpr in monocytes is the same as for macrophages. Proposed therefore is whether the monocytoid cell line THP-1 (7), derived from a monocytic leukemia, may have been a more preferred cell-line to represent monocytes. And for which THP-1 stimulation to a differentiated macrophage phenotype can be achieved by treatment with phorbol ester (8), that would enable comparison of the spectrum of monocyte to macrophage HIV Vpr protein locales¿ to be realised. With the proviso of course that such laboratory cell-line findings are validated against primary monocytes and macrophages.
With the above technicality raised, the present study by Ferrucci et al is an appropriate addition to the field using cell lines that more closely represent those myeloid-lineage cells infected in nature, than earlier cell studies of unrelated lineage, and necessary to demarcate the Vpr cell localisation properties (and possibly other HIV related proteins) of cells infected in vivo.
Virology Journal
Value of cell studies that reflect the natural situation and whether, histiocyte-derived U-937 cells are the cell-line of choice, for studies of HIV infection interactions of monocytes and macrophages
27 October 2011
In the article by Ferrucci et al `Cellular phenotype impacts human immunodeficiency virus type 1 viral protein R subcellular localization¿ Virology Journal 8: 397 (10th of August) 2011 (1), applauded is their approach taken in this study of HIV Vpr protein localization, using cells that more closely represent the types of cells infected in nature as compared to numerous previous studies that deployed laboratory cell-lines (e.g., HeLa cells) derived from cell types that do not naturally harbour HIV infection. The latter approach has undoubtedly been useful and beneficial in many different situations to reveal various important aspects of HIV infection and its interactions. However, given the inherent and specialised compositions and proteome(s) of each different cell type that underpins their size, shapes and activities in the complex body system it is reasonable and pertinent to consider whether for other situations red herring or un-natural blind-ends similarly may have also been collaterally promulgated. And some for which we may still remain in the dark of their true biologic activities in their natural cell environment? Perhaps some of the differences in the HIV Vpr localisation (viz cytoplasmic versus nuclear) between cell types that are representative of naturally infected cells (this present study) versus laboratory manipulated cell targets may have uncovered one such instance.
Accepting the limitations of cell-lines as stand-ins for primary cells such as fresh PBMC¿s, raised is the question of whether U-937 cells is the ideal cell-line choice to in-general and collectively represent native monocytes and differentiated macrophages for HIV studies. As it is well known that there are significant differences in the HIV infection of monocytes and their more differentiated macrophage forms (2), it is unreasonable to lump them together as synonymous entities, and although related should be separately demarcated as monocytes and macrophages. U-937 cells were originally derived and developed from a case of histiocytic lymphoma (3). As such histiocytes (ergo U-937 cells) from bone marrow derived myeloid progenitors (4), differ from monocytes, as they are already well differentiated, and committed resident cells of connective tissue and are relatively inactive and immobile compared with other monocytes/macrophages. Furthermore as U-937 cells express cell surface markers that differ from primary monocytes (5, 6), they poorly represent monocytes. Perhaps a follow up study by these investigators is necessary to establish whether the localisation of Vpr in monocytes is the same as for macrophages. Proposed therefore is whether the monocytoid cell line THP-1 (7), derived from a monocytic leukemia, may have been a more preferred cell-line to represent monocytes. And for which THP-1 stimulation to a differentiated macrophage phenotype can be achieved by treatment with phorbol ester (8), that would enable comparison of the spectrum of monocyte to macrophage HIV Vpr protein locales¿ to be realised. With the proviso of course that such laboratory cell-line findings are validated against primary monocytes and macrophages.
With the above technicality raised, the present study by Ferrucci et al is an appropriate addition to the field using cell lines that more closely represent those myeloid-lineage cells infected in nature, than earlier cell studies of unrelated lineage, and necessary to demarcate the Vpr cell localisation properties (and possibly other HIV related proteins) of cells infected in vivo.
Competing interests
None