Changing of antigenic, imumnogenic and chemical properties of a Coxiella burnetii strain during chick embryo yolk sac passaging.

Coxiella burnetii (C.b.) strain 48 after an increasing number of chick embryo yolk sac (CEYS) passages had lost at egg passages (EP) 15--20 its antigenic, immunogenic and chemical properties typical of phase I. The change refers namely to phase I antibody-inducing ability in mouse, the inability to react in microagglutination (MA) test with the phase II-specific serum, the loss of phase I antibody-binding capacity as detected by immunofluorescence (IF), the capacity to induce an increased number of peritoneal exudate cells (PEC) in the mouse, the resistance to nonspecific phagocytosis by guinea pig macrophages, the polymer two-phase system. At the same time the phase I antibody-inducing ability in rabbit and phase I antibody-binding capacity as detected by the MA and CF tests were preserved up to EP 45, while the phase II antibody-binding capacity in IF and complement-fixation (CF) tests was determined as early as in EP 10 and EP 15, respectively. The changes of other properties, such as splenomegaly and hepatomegaly-inducing abilities as well as immunogenicity by resistance to challenge with phase I virulent cells were more gradual.