Factors affecting the sensitivity and reproducibility of passive haemagglutination test for the quantitation of measles-specific antibodies.

Various factors affecting the passive haemagglutination test (PHA) for the quantitation of measles-specific antibodies have been evaluated with the aim to obtain maximum sensitivity and reproducibility of the test. The antigen used for sensitization was prepared in Vero cells using Edmonston 245 strain of measles virus. Sheep red blood cells (SRBCs) were found most sensitive for use in PHA test. The optimum dilution of tannic acid was found to be 1:40,000 for tanning of fixed and 1:10,000 for unfixed SRBCs, when the tanning was carried out at 4 degrees C overnight. Fixed and tanned SRBCs sensitized with 32 HA units of measles HA antigen at 56 degrees C for 30 mins were found optimal. SRBCs from different sheep affected the sensitivity of the assay. Stability study of SRBCs showed that storage at -70 degrees C of glutaraldehyde-fixed and sensitized SRBCs gave better results as compared to those stored at -20 degrees C and +4 degrees C. Tanned SRBCs could be stored at -70 degrees C only up to 15 days. Sensitized SRBCs with-stood two cycles of freezing and thawing after removal from -20 degrees C and -70 degrees C. Sensitized SRBCs could be stored for 120 days without any significant loss of titer at -20 degrees C, +4 degrees C or 22 degrees C; when lyophilized with stabilizers, there was a slight decline in the titer after exposure at 37 degrees C for 30 days. The lyophilized sensitized SRBCs after reconstitution were found to be stable at +4 degrees C for 3 days without any loss in the titer.(ABSTRACT TRUNCATED AT 250 WORDS)