Inhibition of normal rat macrophage functions by soluble tumor products. Effect of systemic treatment with bacterial immunomodulators

Area of Science:

• Immunology
• Cancer Biology
• Macrophage Function

Background:

• Tumor-bearing rats (TBR) exhibit sera and tumor extracts that inhibit normal macrophage phagocytosis and chemotaxis.
• Bacterial immunomodulators are known to affect immune responses in cancer models.

Purpose of the Study:

• To investigate the effect of bacterial immunomodulator treatment on the inhibitory properties of TBR sera and tumor extracts on normal rat peritoneal macrophages.
• To determine if immunomodulator treatment alters the release of soluble factors from tumor cells that affect macrophage function.

Main Methods:

• Collection of sera and 3 M KCl tumor extracts from normal rats, TBR, and TBR treated with Corynebacterium parvum or Listeria monocytogenes.
• Assay of phagocytic and chemotactic activities of normal rat peritoneal macrophages incubated with these sera and extracts.

Main Results:

• Sera from untreated TBR inhibited both phagocytosis and chemotaxis.
• Sera from C. parvum- or L. monocytogenes-treated TBR showed reduced inhibition of phagocytosis.
• Sera from C. parvum-treated TBR still inhibited chemotaxis, while L. monocytogenes treatment did not.
• Tumor extracts from immunomodulator-treated TBR did not inhibit macrophage phagocytosis or chemotaxis.

Conclusions:

• Treatment with bacterial immunomodulators can reverse or reduce the inhibitory effects of tumor-derived factors on macrophage functions.
• Immunomodulator therapy may influence the production of soluble suppressive factors by tumor cells, thereby restoring macrophage activity.