Counterimmunoelectrophoresis (CIE) is a modification of Ouchterlony method that speeds up migration of an antigen and antibody by applying an electrical current.
Most bacterial antigens are negatively charged in a slightly alkaline environment, whereas antibodies are neutral. When an electric field is applied in an electrophoresis appartus filled with buffer (pH 8.4) and containing known known antibodies and unknown antigens in the agarose well, the antibodies will migrate towards the negative end (cathode) where as antigens will migrate towards the positive end (anode). As the antibody and antigen move towards each other in an electric field, they will soon meet in optimal proportion (zone of equivalence is formed) at some points between the well and visible precipitation occurs.
- Modification of the Ouchterlony method.
- Unknown bacterial antigen and a known specific antibody move towards each other in an electrical field.
- Most bacterial antigen are negatively charged (exceptions Streptococcus pneumoniae serotypes 7 and 14) in a slightly alkaline environment.
- When Ag and Ab meet in optimal proportions, a line of precipitation appear within the agar matrix.
- The entire procedure takes about one hour.
- Any antigen for which antisera is available can be tested by CIE
- Sensivity less than that of particle agglutination (0.01-0.05 mg/ml) of antigen.
Uses of Counterimmunoelectrophoresis
Counterimmunoelectrophoresis is used to detect presence of capsular antigens in CSF of
- H. influenzae
- N. meningitidis
- S. Pneumoniae etc
Demerits of the test:
- CIE is more expensive than agglutination based tests.
- Initial capital outlay for the apparatus
- Need of large quantity of Ag and Ab