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Down-regulation of macrophage lysozyme by lipopolysaccharide and interferon
Abstract:
Lipopolysaccharide (LPS) treatment of resident mouse peritoneal macrophages (M phi) was found to suppress intracellular as well as secreted lysozyme (LZM). Interferon (IFN) had a similar effect. LZM was identified by the capacity of cell lysates or medium to lyse Micrococcus lysodeikticus, and by the presence of a 14.5 Kd protein band which co-migrated with human LZM in SDS-PAGE and which reacted positively in Western blots with antiserum to human LZM. The size of the 14.5 Kd band decreased sequentially with increasing concentrations of LPS to which the cells were exposed. Although the LPS influence on LZM levels was dose-dependent, the intracellular LZM pool responded more readily than secreted LZM. Maximal intracellular LZM suppression of 80% was obtained with 10 micrograms LPS, whereas secreted LZM was reduced by only 66%. An IFN concentration of 100 U reduced secreted LZM by 24%, whereas 10,000 U of IFN decreased the amount of LZM secreted by 71%. Thioglycolate-elicited M phi had 75% less intracellular LZM than untreated resident M phi. Moreover, thioglycolate-elicited M phi were hyporesponsive to the suppressive effects of LPS added in vitro. Because both LPS and IFN have been shown to stimulate numerous M phi functions, the data are of interest because they support the concept, based on other studies, that agents which are capable of enhancing some M phi activities may concomitantly down-regulate other functions.
Insights
Lipopolysaccharide (LPS) and Interferon (IFN) suppress lysozyme (LZM) levels in mouse macrophages. This study shows that while some macrophage functions are enhanced by these agents, others, like LZM production, are downregulated.
Area of Science:
- Immunology
- Cell Biology
Background:
- Macrophages play a crucial role in innate immunity.
- Lysozyme (LZM) is a key enzyme in the antimicrobial defense system of macrophages.
- Lipopolysaccharide (LPS) and Interferon (IFN) are known immune modulators.
Purpose of the Study:
- To investigate the effect of LPS and IFN on intracellular and secreted LZM levels in mouse macrophages.
- To examine the responsiveness of different macrophage populations to LPS and IFN-induced LZM suppression.
Main Methods:
- Treatment of mouse peritoneal macrophages with varying concentrations of LPS and IFN.
- Quantification of LZM activity using Micrococcus lysodeikticus lysis assay.
- Identification and molecular weight analysis of LZM protein using SDS-PAGE and Western blotting.
- Comparison of LZM levels in resident and thioglycolate-elicited macrophages.
Main Results:
- LPS and IFN significantly suppressed both intracellular and secreted LZM in a dose-dependent manner.
- Intracellular LZM was more readily suppressed by LPS than secreted LZM.
- Thioglycolate-elicited macrophages exhibited lower basal LZM levels and were hyporesponsive to LPS-induced suppression.
- A 14.5 Kd protein band, identified as LZM, decreased in size with increasing LPS concentration.
Conclusions:
- LPS and IFN downregulate LZM production in macrophages, indicating a complex regulatory role in immune cell function.
- These findings support the concept that immune-stimulating agents can simultaneously suppress certain macrophage activities.
- The differential response of macrophage populations highlights the heterogeneity in immune cell function and regulation.