Testing Vaccines by the Complement Fixation Test for Avian Leukosis Virus Using a Short Cell Culture Passage Interval

Abstract

SUMMARY The current complement fixation for avian leukosis (COFAL) test for screening veterinary vaccines requires a 21-day maintenance period of chick embryo (CE) cell cultures. The method described requires only 9 days. The two methods gave similar sensitivity. Also, starting the test with primary cells was as good as starting with secondary cells in contributing to the sensitivity of the test. The COFAL test was originally described by Sarma, Turner and Huebner (2). This is a two-part procedure: propagation of lymphoid leukosis virus on chick embryo cell cultures; and detection of the antigen by a microtiter complement-fixation technique. The current vaccine screening test (3) of the Veterinary Biologics Division requires 21 days for virus propagation. The complement fixation part of the test is adapted from the method described in Public Health Monograph No. 74 (4). Furminger and Beale (1) compared the sensitivity of the COFAL test and the Rubin interference test. In using the COFAL test for detection of Rous-associated virus (RAV)-1 in chick embryo cells (keeping their cell cultures in a state of maximum growth by subculturing every third or fourth day) they found that the virus, diluted to its endpoint of 10-7, was detected by the 11th day. By contrast, in unpassaged cells the highest dilution in which the virus was detected was 10-4 after 14 days of incubation. In comparing the 9-day propagation time with the 21-day propagation time, tenfold dilutions of RAV-1 and RAV-2 (prototypes for subgroup A and subgroup B lymphoid leukosis viruses) were made and secondary CE cell cultures were inoculated. The materials and methods were as described in Veterinary Biologics