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Immunoregulatory role of in vitro differentiated macrophages on human natural killer (NK)-cell activity
Z L Chang1, T L Whiteside, R B Herberman
1Department of Pathology, University of Pittsburgh School of Medicine, Pennsylvania 15213.
Abstract:
Immunoregulatory effects of human macrophages on natural killer (NK) activity were studied. Monocytes were isolated by adherence to plastic, after leukapheresis of normal blood donors, and cultured for 1 to 14 days. In vitro-differentiated (5-7 days) human macrophages consistently and significantly (P less than 0.01) augmented NK activity of fresh autologous or allogeneic PBMNC. During culture, these macrophages also developed increased antitumor cytostatic activity. The optimal time for both the expression of cytostatic activity and up-regulation of NK activity was 5-7 days in culture. In contrast, 12- to 14-day macrophages significantly suppressed NK activity and had less cytostatic activity. Macrophages in culture demonstrated shifts in Leu-M3+HLA-DR+ phenotype from the mean of 60% +/- 11 (SD) in fresh monocytes to 90% +/- 5 between Days 5 and 7 in culture and then down to 10% +/- 5 in 14-day cultures. The activity of NK (CD56+CD3-) cells, purified by Percoll gradient centrifugation and flow cytometry, was up-regulated directly by in vitro-differentiated macrophages at low macrophage to NK cell ratios, and this up-regulation was not dependent on T lymphocytes or other accessory cells. The modulation of NK activity by differentiated macrophages was not MHC-restricted and depended on the viability and cellular integrity of macrophages. Sonicated macrophages could no longer up-regulate NK activity. This study shows that antitumor effects mediated by human in vitro differentiated LeuM3+HLA-DR+ macrophages may simultaneously involve more than one mechanism, namely direct cytostasis of tumor cells and activation of NK cells.
Insights
Human macrophages can boost natural killer (NK) cell activity and antitumor effects when differentiated in vitro for 5-7 days. Older macrophages (12-14 days) suppress NK activity, indicating a time-dependent immunomodulatory role.
Area of Science:
- Immunology
- Cell Biology
- Cancer Research
Background:
- Human macrophages play a critical role in immune regulation.
- Natural Killer (NK) cells are crucial for innate immunity and tumor surveillance.
- Understanding macrophage-NK cell interactions is key to developing immunotherapies.
Purpose of the Study:
- To investigate the immunoregulatory effects of in vitro-differentiated human macrophages on NK cell activity.
- To determine the impact of macrophage differentiation time on their ability to modulate NK cell function and antitumor effects.
Main Methods:
- Isolation and in vitro culture of human monocytes to differentiate into macrophages over 14 days.
- Assessment of NK cell activity using autologous or allogeneic peripheral blood mononuclear cells (PBMNC).
- Phenotypic analysis of macrophages (Leu-M3+, HLA-DR+) and NK cells (CD56+, CD3-) using flow cytometry.
- Evaluation of macrophage cytostatic activity against tumor cells.
Main Results:
- Macrophages differentiated for 5-7 days significantly augmented NK activity and developed antitumor cytostatic effects.
- Optimal NK cell activation and cytostasis occurred at 5-7 days of macrophage differentiation.
- Macrophages cultured for 12-14 days suppressed NK activity and showed reduced cytostatic potential.
- Macrophage-mediated NK cell up-regulation was direct, not MHC-restricted, and dependent on macrophage viability.
Conclusions:
- In vitro-differentiated macrophages exhibit time-dependent immunomodulatory effects on NK cells.
- Early-stage differentiated macrophages (5-7 days) enhance NK cell activity and antitumor functions.
- Late-stage differentiated macrophages (12-14 days) exhibit immunosuppressive properties.
- Macrophage-mediated antitumor effects involve direct tumor cell cytostasis and NK cell activation.