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Human astrocytes express membrane cofactor protein (CD46), a regulator of complement activation
D L Gordon1, T A Sadlon, S L Wesselingh
1Department of Microbiology and Infectious Diseases, Flinders Medical Center, Bedford Park, South Australia.
Abstract:
Expression of membrane cofactor protein (CD46) on cultured human astrocytes was demonstrated by indirect immunofluorescence microscopy and flow cytometry following staining with a monoclonal antibody specific for CD46. Western transfer and immunoblotting detected a doublet of Mr 66,000 and 56,000. Analysis of astrocyte mRNA revealed the presence of multiple alternatively spliced transcripts encoding different extracellular regions or cytoplasmic tails of CD46. Astrocytes were also shown to express decay accelerating factor, but not the type 1 complement receptor. Upregulation of astrocyte CD46 occurred following cytomegalovirus infection. These results indicate that astrocytes express proteins involved in regulation of complement activation and protection against autologous complement.
Insights
Human astrocytes express membrane cofactor protein (CD46) and decay accelerating factor, proteins that regulate complement activation. Cytomegalovirus infection upregulates CD46 expression on astrocytes, suggesting a role in complement protection.
Area of Science:
- Neuroimmunology
- Complement biology
- Cellular immunology
Background:
- Astrocytes play crucial roles in central nervous system immunity.
- The complement system is a key component of innate immunity with implications in neurological diseases.
- Understanding complement regulatory protein expression on astrocytes is vital for neuroinflammatory research.
Purpose of the Study:
- To investigate the expression and function of complement regulatory proteins, specifically membrane cofactor protein (CD46), on human astrocytes.
- To determine if astrocyte CD46 expression is altered during viral infection, such as by cytomegalovirus.
Main Methods:
- Indirect immunofluorescence microscopy and flow cytometry were used to detect CD46 expression on cultured human astrocytes.
- Western transfer and immunoblotting identified the molecular weight of CD46.
- Analysis of astrocyte messenger RNA (mRNA) identified alternatively spliced CD46 transcripts.
- Expression of decay accelerating factor and type 1 complement receptor was also assessed.
Main Results:
- Human astrocytes express membrane cofactor protein (CD46), detected as a doublet of Mr 66,000 and 56,000.
- Multiple alternatively spliced CD46 transcripts were found in astrocytes.
- Astrocytes express decay accelerating factor but not the type 1 complement receptor.
- Cytomegalovirus infection led to the upregulation of CD46 expression on astrocytes.
Conclusions:
- Astrocytes express key proteins, including CD46 and decay accelerating factor, that regulate complement activation.
- Astrocyte CD46 expression is upregulated following cytomegalovirus infection.
- These findings suggest that astrocytes possess mechanisms to protect themselves against autologous complement-mediated damage.