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Activation of macrophage function by intraperitoneal administration of the streptococcal antitumor agent OK-432
Abstract:
Motility, adhesiveness, IL1 production, and inhibition of tumor cell growth in vitro were examined in murine peritoneal macrophages obtained after intraperitoneal injection of a streptococcal preparation OK-432, heat-inactivated OK-432 (HI-OK-432), and thioglycollate medium (TG). By varying the interval between intraperitoneal injection of OK-432 and the harvest of peritoneal macrophages, it was found that OK-432 induced a time-dependent multi-step alteration of these properties: step I increased motility on day 1: step II increased adhesiveness on day 2; and step II increased inhibition of tumor cell growth and IL1 production. During step III, the peritoneal macrophage population, including Ia-bearing cells, increased dramatically in the peritoneal cavities of OK-432-treated mice. In contrast, injection of either HI-OK-432 or TG, which lack antitumor activity in vivo, initiated steps I and II, but not step III. The Ia-bearing macrophages induced by OK-432 showed high ability of IL1 production, but low growth inhibitory activity against tumor cells. Based on these results, OK-432 seems to be performing a dual function: eliciting a new population of macrophages to the site of injection (heat stable function), and inducing two different populations of antitumor macrophages and Ia-bearing macrophages (heat unstable function).
Insights
Streptococcal preparation OK-432 enhances macrophage antitumor activity through a time-dependent, multi-step process. This involves increased motility, adhesion, IL1 production, and tumor cell growth inhibition, distinct from heat-inactivated OK-432 or thioglycollate medium.
Area of Science:
- Immunology
- Cancer Research
- Microbiology
Background:
- Murine peritoneal macrophages play a crucial role in immune responses.
- The streptococcal preparation OK-432 is known to modulate immune cells.
- Understanding macrophage activation is key to developing cancer therapies.
Purpose of the Study:
- To investigate the time-dependent effects of OK-432 on murine peritoneal macrophage functions.
- To compare the effects of active OK-432 with heat-inactivated OK-432 (HI-OK-432) and thioglycollate medium (TG).
- To elucidate the dual functions of OK-432 in macrophage recruitment and activation.
Main Methods:
- Intraperitoneal injection of OK-432, HI-OK-432, or TG into mice.
- Harvesting peritoneal macrophages at various time intervals post-injection.
- Assessing macrophage motility, adhesiveness, IL1 production, and inhibition of tumor cell growth in vitro.
Main Results:
- OK-432 induced a time-dependent, multi-step alteration in macrophage properties: increased motility (day 1), increased adhesiveness (day 2), and enhanced IL1 production and tumor cell growth inhibition (step III).
- Step III, characterized by a dramatic increase in peritoneal macrophages including Ia-bearing cells, was specific to active OK-432.
- HI-OK-432 and TG induced only early steps (motility and adhesiveness) but lacked the ability to induce step III and antitumor activity in vivo.
Conclusions:
- OK-432 exhibits a dual function: a heat-stable function for macrophage recruitment and a heat-unstable function for inducing distinct antitumor and Ia-bearing macrophage populations.
- The Ia-bearing macrophages induced by OK-432 are potent IL1 producers but have limited tumor growth inhibitory activity.
- These findings highlight OK-432's complex immunomodulatory role and potential in cancer immunotherapy.