Specific lysis ofTheileria annulata‐infectedlymphoblastoid cells by a monoclonal antibody recognizing an infection‐associated antigen

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Abstract
SummaryA monoclonal antibody (4H5) recognizing aTheileria annulatainfection‐associated antigen was assayed to see if it could either suppress the proliferation ofT. annulata‐infectedlymphoblastoid cells, as monitored by the incorporation of triated thymidine by proliferating host cells, or lyseT. annulata‐infectedlymphoblastoid 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 theT. annulataHissar‐infected cell line against which this monoclonal antibody was raised. This effect extended both to other (allogeneic)T. annulataHissar‐infected cell lines and to lymphoblastoid cell lines infected with other geographical stocks ofT. annulata.An uninfected bovine lymphoid cell line was not affected by the antibody. The results obtained in thesein vitroexperiments are taken to mean that binding of the monoclonal antibody 4H5 to aT. annulatainfection‐associated antigen, in the presence of complement, will lyse and suppress specifically the proliferation ofT. annulata‐infectedlymphoblastoid cells. These observations raise the possibility that immunization of cattle with the purifiedT. annulatainfection‐associated antigen recognized by this monoclonal antibody may provoke immune responses which are capable of suppressing the proliferation ofT. annulata‐infectedlymphoblastoid cellsin vivoand thus provide an effective method of immunoprophylaxis against tropical theileriosis.