Typing of ECHO Viruses by a Complement Fixation Technic

Abstract

Typing of ECHO viruses(1) by standard neutralization tests is an inconvenient and laborious procedure because of large number of prototypes. Recent findings, that complement-fixing (CF) antigens for ECHO viruses could be prepared consistently from monkey kidney tissue cultures and that these antigens reacted type specifically with ECHO antisera prepared in guinea pigs and monkeys(2), suggested the possibility of typing ECHO virus isolates by means of a CF technic. This preliminary report describes simple methods which have been successful in typing 28 ECHO virus isolates by such a procedure.†

Methods. CF antigens were prepared by inoculating each of 4 rhesus kidney tissue culture tubes containing 1 ml of the following: lactalbumin hydrolysate 0.5%, calf serum 2%, Earle's solution 97.5%, with 0.1 ml of undiluted fluid from the original or an early monkey kidney passage of the ECHO isolate. After complete degeneration of tissue had taken place, the tubes were frozen and thawed, and pooled tissue culture fluid from these tubes was used as antigen without centrifugation. Of 28 ECHO virus isolates tested, 15 were from a Washington, D.C. welfare institution(3), and 13 were from other sources in Washington, D.C., and from other localities in U.S. and England (ECHO type 9).‡ All were typed originally by neutralization tests except the ECHO type 10 isolates. The latter, however, produced the unique cytopathogenic effect characteristic of the prototype strain of ECHO 10 virus. The CF typing tests for most strains were done without prior knowledge of the neutralization test data. ECHO antisera used in CF tests had been prepared in monkeys (4).§ Homotypic and heterotypic CF titers of these sera against CF antigens of ECHO prototype strains prepared in monkey kidney tissue culture are published elsewhere(2).