title: Detection of rabies virus antigen or antibody using flow cytometry.
abstract: BACKGROUND
  Rabies is invariably a fatal encephalomyelitis that is considered to be a serious public health problem. Rabies diagnosis must be rapid and conclusive. Detection and quantification of antirabies antibodies is used for assessment of the effectiveness of rabies vaccines. Hence, computer-automated detection of fluorescence using flow cytometry was attempted to reduce the work time required to undertake the conventional rapid fluorescent focus inhibition test (RFFIT).
  
  
  METHODS
  Pasteur virus (PV)-infected mouse neuroblastoma (MNA) cells were stained with rabies virus antinucleocapsid antibody, fluorescein isothiocyanate (FITC) conjugate, and the percentage of infected cells at 24, 48, and 72 h postinfection (PI) was determined using flow cytometry. Serum samples containing known antibody titres estimated by RFFIT in terms of IU/ml were used to neutralize 50 FFD50 dose of PV. The percentage of MNA cells infected by the un-neutralized virus was estimated by flow cytometry. Using the value of the percentage of cells infected in the presence of known negative serum as 100%, the infection inhibition caused by antibodies at each dilution of positive reference serum was calculated and a regression equation generated for the prediction of rabies virus antibody titres in test sera samples as equivalent units per ml (EU/ml).
  
  
  RESULTS
  There was a significant increase in the percentage of infected cells between 24 and 48 h PI from 26.45 to 75.28%. The percentage of cells having high side scatter was also highest at 72 h PI (11.11%). Antibody titres predicted by flow cytometry and those estimated by RFFIT as IU/ml showed a correlation coefficient of 0.74.
  
  
  CONCLUSIONS
  Thus, flow cytometry could be used to detect rabies virus antigen in infected cells and to predict serum antibody titres from a single dilution of serum tested with the potential advantages of automation, rapidity, and lack of subjectivity. It has the potential to replace the time-tested RFFIT in rabies serology in the years to come.
authors.affiliation: Department of Animal Biotechnology, Madras Veterinary College, Tamil Nadu Veterinary and Animal Sciences University, Chennai 600007, India.
authors.forename: Dayalan
authors.initials: D
authors.lastname: Vengatesan
authors.forename: Gopal Dhinakar
authors.initials: GD
authors.lastname: Raj
authors.forename: Angamuthu
authors.initials: A
authors.lastname: Raja
authors.forename: Pachaikani
authors.initials: P
authors.lastname: Ramadass
authors.forename: Lakshmanaswamy
authors.initials: L
authors.lastname: Gunaseelan
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D000956:Antigens, Viral / Q000097:blood*; D004285:Dogs; D005434:Flow Cytometry / Q000379:methods*; D005455:Fluorescent Antibody Technique / Q000379:methods; D051379:Mice; D009500:Neutralization Tests; D011818:Rabies / Q000175:diagnosis*; D011819:Rabies Vaccines / Q000276:immunology; D011820:Rabies virus / Q000276:immunology / Q000302:isolation & purification*; D012016:Reference Values; D012680:Sensitivity and Specificity
chemical_list: D000914:Antibodies, Viral; D000956:Antigens, Viral; D011819:Rabies Vaccines