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Morphological study of cytotoxicity produced by PSK-induced polymorphonuclear leukocytes (PMNs) and Nocardia rubra
1First Department of Internal Medicine, Kyoto Prefectural University of Medicine, Japan.
Abstract:
The morphologic changes in PMNs induced by an i.p. injection of PSK, a polysaccharide from the mycelia of Coriolus versicolor, and tumor cells undergoing cell death, were evaluated by immunohistochemical staining and electron microscopy. Male C3H/He mice, 8-10 -weeks old, received an i.p. injection of 125 mg/kg of PSK. Their PMNs were obtained 6 h after the PSK injection by peritoneal lavage. N-CWS (Nocardia rubra cell wall skeleton) was added at the start of the chromium release assay using the MM46 mammary carcinoma cell line, which is syngeneic to C3H/He mice, as target cells. During the cytotoxic assay, the cells were fixed at various time points. The MM46 cells expressed ICAM-1 while the PMNs expressed both ICAM-1 and LFA-1 as determined by immunohistochemical staining and immunoelectron microscopy using anti-ICAM-1 and anti-LFA-1 antibodies. PMNs with ruffle-like microvilli adhered to the MM46 tumor cells 30 min after the addition of N-CWS. Immunoelectron microscopic findings suggested that the adhesion molecules were LFA-1 on the PMNs and ICAM-1 on the MM46 tumor cells, but cell fusion between the PMNs and tumor cells was not observed. The MM46 tumor cells gradually lost their microvilli, which showed cell damage, and died 6-7 h after the addition of the N-CWS. This time course of tumor cell death is compatible with the results of the cytotoxic assay. Pretreatment of PMNs by anti-LFA-1 antibody suppressed 1% lysis of MM46 tumor cells from 90% to 10% (p < 0.01). These data suggest that adhesion molecule on the surface of PMNs such as LFA-1 might play an important role on signal transduction of these PMNs cytotoxic function in this experimental system.
Insights
Polysaccharide K (PSK) from Coriolus versicolor induces changes in polymorphonuclear leukocytes (PMNs) that enhance their cytotoxic function against tumor cells. The adhesion molecule LFA-1 on PMNs is crucial for this tumor cell killing mechanism.
Area of Science:
- Immunology
- Cell Biology
- Pharmacology
Background:
- Polysaccharide K (PSK), derived from Coriolus versicolor, is known for its immunomodulatory effects.
- Polymorphonuclear leukocytes (PMNs) play a role in immune responses, including anti-tumor activity.
- Understanding the mechanisms of PSK-induced anti-tumor effects is crucial for developing novel cancer therapies.
Purpose of the Study:
- To investigate the morphologic changes in PMNs induced by PSK.
- To elucidate the role of adhesion molecules in PSK-mediated PMN cytotoxicity against tumor cells.
- To evaluate the contribution of LFA-1 and ICAM-1 in the interaction between PMNs and tumor cells.
Main Methods:
- Immunohistochemical staining and electron microscopy were used to examine PMN morphology and adhesion molecules.
- A chromium release assay was employed to measure PMN cytotoxicity against MM46 mammary carcinoma cells.
- Antibodies against LFA-1 and ICAM-1 were used to block adhesion molecule function.
Main Results:
- PSK treatment induced morphologic changes in PMNs, including ruffle-like microvilli.
- PMNs expressed LFA-1 and MM46 tumor cells expressed ICAM-1, facilitating adhesion.
- Blocking LFA-1 significantly reduced PMN-mediated tumor cell lysis, indicating its critical role.
Conclusions:
- PSK enhances PMN cytotoxic function through mechanisms involving adhesion molecules.
- LFA-1 on PMNs and ICAM-1 on tumor cells are key mediators of PMN-tumor cell interaction and subsequent cell death.
- These findings highlight the potential of PSK as an immunotherapeutic agent targeting PMN-mediated anti-tumor responses.