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Aflatoxin B(1) inhibits CD14-mediated nitric oxide production in murine peritoneal macrophages
1College of Pharmacy, Sungkyunkwan University, 300, Chunchun-dong Suwon City, South Korea.
Abstract:
Aflatoxin B(1) (AFB(1)), a potent hepatocarcinogen, has been known to impair non-specific and specific immunity. Macrophages play an important role in host defense against tumors and microorganisms and a number of compounds are implicated in macrophage cytotoxicity. Since activated by the reaction of LPS with CD14, macrophages produce nitric oxide (NO) that is a cytotoxic effector molecule in cell killing. In the present study, we investigated whether the alteration of CD14 level on macrophages by AFB(1) affects NO production in murine peritoneal macrophages. When macrophages were stimulated with LPS after AFB(1)-pretreatment, or they were co-treated with LPS and AFB(1), the NO production decreased in a dose-dependent manner. In contrast, when macrophages were post-treated with AFB(1) after LPS-stimulation, NO production was unchanged. DNA, RNA, and protein synthesis were reduced by AFB(1)-pretreatment of macrophages. The addition of anti-CD14 antibodies to the cultures decreased NO production further. FACS analysis showed that the binding of anti-CD14 antibodies to the macrophages was suppressed by AFB(1)-pretreatment followed by LPS-stimulation. However, AFB(1) does not alter the binding anti-CD14 antibodies to the macrophages without LPS-stimulation. In contrast, AFB(1) pretreatment increased an amount of CD14 released in culture medium. Taken together, these data indicate that the reduced NO production in murine peritoneal macrophages by AFB(1)-pretreatment is related to the suppressed expression of CD14 on macrophage membrane and to the increased secretion of it to culture medium after LPS-stimulation.
Insights
Aflatoxin B(1) exposure reduces nitric oxide (NO) production by macrophages, a key immune response. This occurs because AFB(1) alters CD14 levels, impairing macrophage function.
Area of Science:
- Immunology
- Toxicology
- Cell Biology
Background:
- Macrophages are crucial for host defense, producing nitric oxide (NO) for cytotoxicity.
- Aflatoxin B(1) (AFB(1)) is a hepatocarcinogen known to suppress immune functions.
- CD14 is essential for macrophage activation by lipopolysaccharide (LPS) to produce NO.
Purpose of the Study:
- To investigate how AFB(1) affects CD14 levels on macrophages.
- To determine the impact of AFB(1)-induced CD14 alterations on NO production.
- To elucidate the mechanism by which AFB(1) modulates macrophage-mediated cytotoxicity.
Main Methods:
- Murine peritoneal macrophages were pre-treated, co-treated, or post-treated with AFB(1) and LPS.
- Nitric oxide production was measured using standard assays.
- Flow cytometry (FACS) was used to analyze CD14 expression and antibody binding.
- DNA, RNA, and protein synthesis were assessed to evaluate cellular effects.
Main Results:
- AFB(1) pre-treatment or co-treatment with LPS significantly decreased NO production in a dose-dependent manner.
- Post-treatment with AFB(1) after LPS stimulation did not affect NO production.
- AFB(1) reduced DNA, RNA, and protein synthesis in macrophages.
- AFB(1) pretreatment suppressed CD14 expression on the macrophage surface and increased its release into the culture medium upon LPS stimulation.
Conclusions:
- AFB(1) impairs macrophage NO production by downregulating CD14 expression and increasing its secretion.
- These alterations in CD14 contribute to the immunosuppressive effects of AFB(1).
- Understanding these mechanisms is vital for addressing AFB(1) toxicity and immune dysfunction.