Specific lysis of Theileria annulata-infected lymphoblastoid cells by a monoclonal antibody recognizing an infection-associated antigen.

A monoclonal antibody (4H5) recognizing a Theileria annulata infection-associated antigen was assayed to see if it could either suppress the proliferation of T. annulata-infected lymphoblastoid cells, as monitored by the incorporation of tritiated thymidine by proliferating host cells, or lyse T. annulata-infected lymphoblastoid cells, as assessed by counts of target cell numbers and examination of Giemsa stained smears. These assays showed that binding of the monoclonal antibody, in the presence of complement, both lysed and suppressed the proliferation of the T. annulata Hissar-infected cell line against which this monoclonal antibody was raised. This effect extended both to other (allogeneic) T. annulata Hissar-infected cell lines and to lymphoblastoid cell lines infected with other geographical stocks of T. annulata. An uninfected bovine lymphoid cell line was not affected by the antibody. The results obtained in these in vitro experiments are taken to mean that binding of the monoclonal antibody 4H5 to a T. annulata infection-associated antigen, in the presence of complement, will lyse and suppress specifically the proliferation of T. annulata-infected lymphoblastoid cells. These observations raise the possibility that immunization of cattle with the purified T. annulata infection-associated antigen recognized by this monoclonal antibody may provoke immune responses which are capable of suppressing the proliferation of T. annulata-infected lymphoblastoid cells in vivo and thus provide an effective method of immunoprophylaxis against tropical theileriosis.