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Clearance of myelin basic protein from blood of normal and EAE rabbits
Abstract:
The rate of clearance of porcine myelin basic protein (MBP) from plasma of rabbits was determined following intravenous injection of 20 mg MBP. The MBP level in the plasma was measured by a 2-site immunoradiometric assay with specific antibody to guinea pig MBP produced in rabbits. Plasma MBP-antibody levels were determined by competitive binding radioimmune assay (RIA). Unsensitized and those sensitized with complete Freund's adjuvant (CFA), with porcine MBP in CFA, and with whole porcine spinal cord in CFA were studied. Unsensitized and CFA sensitized rabbits exhibited maximum MBP levels in the plasma within two minutes after injection with rapid decrease to undetectable levels in one hour. Thirty-nine of the unsensitized (control) rabbits exhibited normal, rapid clearance and no subsequent physical signs of EAE while one of the control rabbits exhibited a slightly retarded clearance rate. Histologic examination of autopsy tissues from the control group revealed that five rabbits showed lesions which could be attributed to Encephalitozoan cuniculi or Toxoplasma and one rabbit autopsied 65 days after clearance had minimal EAE lesions. Rabbits sensitized with MBP exhibited a retarded rate of clearance at the acute stage of EAE and following recovery. Rabbits sensitized with whole spinal cord in CFA also exhibited a retarded rate of MBP clearance. Anti (MBP) antibodies were detected in the plasma of all rabbits which exhibited a retarded rate of MBP clearance. Significant rates of retardation were not detected until approximately three weeks after sensitization with CFA-MBP or CFA-spinal cord. While MBP antibody levels in most animals were not detected by the immunodiffusion technique, antibodies were demonstrated by RIA. The 20 mg MBP given intravenously is probably in great antigen excess and conducive to the formation of soluble MBP-anti (MBP) complexes in the blood.
Insights
The clearance rate of myelin basic protein (MBP) is slower in rabbits sensitized with MBP or spinal cord, correlating with the presence of anti-MBP antibodies. This suggests a role for immune complexes in MBP clearance during experimental autoimmune encephalomyelitis (EAE).
Area of Science:
- Neuroimmunology
- Protein Metabolism
- Autoimmune Diseases
Background:
- Myelin basic protein (MBP) is a key autoantigen in experimental autoimmune encephalomyelitis (EAE).
- Understanding MBP clearance kinetics is crucial for elucidating EAE pathogenesis.
Purpose of the Study:
- To investigate the plasma clearance rate of porcine myelin basic protein (MBP) in rabbits.
- To determine the correlation between MBP clearance, sensitization protocols, and antibody production.
Main Methods:
- Intravenous injection of 20 mg porcine MBP into rabbits.
- Measurement of plasma MBP levels using a 2-site immunoradiometric assay.
- Quantification of anti-MBP antibodies via competitive binding radioimmune assay (RIA).
- Comparison of clearance rates in unsensitized, CFA-sensitized, MBP-sensitized, and spinal cord-sensitized rabbits.
Main Results:
- Unsensitized and CFA-sensitized rabbits showed rapid MBP clearance within one hour.
- Rabbits sensitized with MBP or whole spinal cord exhibited retarded MBP clearance, particularly during the acute EAE stage.
- Retarded MBP clearance correlated with the presence of anti-MBP antibodies detected by RIA.
- Antibodies were detected approximately three weeks post-sensitization.
Conclusions:
- Sensitization with MBP or spinal cord retards MBP plasma clearance in rabbits.
- The formation of MBP-antibody complexes likely influences MBP clearance kinetics.
- RIA is a sensitive method for detecting anti-MBP antibodies relevant to EAE pathogenesis.