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Anti-liver-kidney microsome antibody recognizes a 50,000 molecular weight protein of the endoplasmic reticulum
Abstract:
Children with autoimmune chronic active hepatitis may have high titers of antibodies detected by immunofluorescence staining of hepatocytes and tubular cells in rat liver and kidney sections, respectively. These antibodies are directed against antigens contained in microsomal fractions prepared from these two organs. We have found that sera from these patients recognized a 50,000 mol wt protein present in higher concentration in smooth microsome subfractions compared with rough microsome subfractions. This protein is an integral membrane protein and is not glycosylated. It is exposed on the cytoplasmic face of the endoplasmic reticulum and is rather resistant to proteolysis with proteinase K. Since patients with liver disease of different etiology and similar severity of cell lysis do not give rise to liver-kidney microsome antibody (LKMA), lysis of hepatocytes is apparently not a sufficient condition for their development.
Insights
Children with autoimmune hepatitis produce antibodies targeting a specific liver microsomal protein. This protein, identified as a 50,000 mol wt integral membrane protein, is crucial for diagnosing this autoimmune liver disease.
Area of Science:
- Immunology
- Hepatology
- Molecular Biology
Background:
- Autoimmune chronic active hepatitis in children can be associated with high antibody titers.
- These antibodies are detected against antigens in microsomal fractions of liver and kidney.
- Liver-kidney microsome antibody (LKMA) is a key diagnostic marker.
Purpose of the Study:
- To identify the specific antigen recognized by LKMA in children with autoimmune chronic active hepatitis.
- To characterize the properties of this antigen.
Main Methods:
- Immunofluorescence staining of rat liver and kidney sections.
- Analysis of microsomal fractions using protein assays.
- Characterization of the antigen's molecular weight, glycosylation, and cellular localization.
Main Results:
- Sera from patients recognized a 50,000 mol wt protein in microsomal fractions.
- This protein was more concentrated in smooth microsomes than rough microsomes.
- The antigen is an integral membrane protein, not glycosylated, located on the cytoplasmic face of the endoplasmic reticulum, and resistant to proteinase K.
- Hepatocyte lysis alone does not induce LKMA development.
Conclusions:
- The primary target antigen for LKMA in autoimmune chronic active hepatitis is a 50,000 mol wt integral membrane protein.
- This protein is localized to the endoplasmic reticulum.
- The presence of LKMA is specific to autoimmune liver disease and not solely dependent on hepatocyte damage.