Immunological aspects of Theileria annulata infection in calves.  1.  E., EA, and EAC rosette forming cells in calves infected with T. annulata. 
Peripheral blood lymphocytes (PBLs) from normal and Theilaria annulata-infected calves were assayed for E, EA, and EAC rosette formation.  The E rosette forming cells showed the first increase on day 8 of the infection.  This continued in all animals till day 14 the maximum increase was recorded.  After that they showed reduced percentages of E rosettes, reaching normal values (as obtained before the infection) on day 24 to 30.  When the recovered animals were challenged 64 days after the first infection, an increase in the percentage of E rosette formation was again observed.  Although a moderate increase in the percentage of EAC rosette formation was recorded the tendency was the same as for E rosettes in regard to the course of the infection.  In contrast to E rosettes, EAC rosettes remained constant during the challenge infection.  The EA rosette forming cells generally had the same tendency as E rosettes during both the first and the challenge infection.