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Published on: August 15, 2012
Responses of microglia in vitro to the gram-positive bacterial component, lipoteichoic acid
Ya-Fen Jiang-Shieh1, Kuei-Ying Yeh, I-Hua Wei
1Department of Anatomy, National Cheng Kung University Medical College, Tainan, Taiwan.
Abstract:
An increase in incidence and severity of gram-positive infections has emerged in the past decade. In this regard, attention has been focused recently on immune responses of microglial cells in the central nervous system to gram-positive bacteria. The underlying immunological and cellular events in microglial activation induced by specific bacterial toxin of gram-positive bacteria, however, have not yet been clarified fully. This study reports that a simple cell wall product, lipoteichoic acid (LTA), derived from gram-positive bacteria (Staphylococcus aureus) could trigger microglial activation in vitro. Microglia challenged with LTA showed intense ruffling of plasma membrane in the form of lamellipodia or rounded up forming cell aggregates. MTT assay and Western blot analysis with anti-proliferating cell nuclear antigen antibody showed a significant microglial proliferation that may be induced at the later phases of LTA treatment with low doses but at the early period with a high dose. Concentrated LTA also caused apoptotic death of cultured microglia showing fragmented nuclei and increased expression of annexin V or caspase 3. In response to LTA, isolated microglia increased the expression of inducible nitric oxide synthase and major histocompatibility complex class II antigen. Microglial LTA receptors such as CD14 molecule, complement receptor type 3, and macrophage scavenger receptor were upregulated concurrently. In conclusion, staphylococcal LTA can exert an immunomodulatory effect on microglial morphology, cell cycle, and immunomolecules, including its receptors.
Insights
Lipoteichoic acid (LTA) from Staphylococcus aureus activates microglia, influencing their morphology, proliferation, and immune molecule expression. This study clarifies the central nervous system immune response to gram-positive bacterial components.
Area of Science:
- Neuroimmunology
- Microbiology
- Cellular Biology
Background:
- Rising incidence and severity of gram-positive bacterial infections.
- Growing interest in microglial cell immune responses in the central nervous system (CNS) to gram-positive bacteria.
- Incomplete understanding of microglial activation mechanisms by gram-positive bacterial toxins.
Purpose of the Study:
- To investigate the in vitro effects of lipoteichoic acid (LTA), a cell wall component of gram-positive bacteria, on microglial cells.
- To elucidate the immunological and cellular events underlying microglial activation induced by LTA.
Main Methods:
- In vitro challenge of primary microglia with lipoteichoic acid (LTA) from Staphylococcus aureus.
- Morphological analysis of microglial activation (ruffling, aggregation).
- MTT assay and Western blot for assessing microglial proliferation (PCNA expression).
- Assessment of apoptosis (annexin V, caspase 3 expression, nuclear fragmentation).
- Analysis of immune molecule expression (iNOS, MHC class II) and microglial receptor upregulation (CD14, CR3, MSR).
Main Results:
- LTA induced significant microglial activation, including membrane ruffling and aggregation.
- Microglial proliferation was observed, dependent on LTA dose and treatment duration.
- High LTA concentrations led to microglial apoptosis.
- LTA upregulated key immune molecules (iNOS, MHC class II) and microglial receptors (CD14, CR3, MSR).
Conclusions:
- Staphylococcal LTA effectively triggers microglial activation in vitro.
- LTA modulates microglial morphology, cell cycle progression, and the expression of immunomodulatory molecules and receptors.
- These findings highlight LTA's role in CNS immune responses to gram-positive bacteria.
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