PERIPHERAL-BLOOD LYMPHOCYTE PROLIFERATIVE RESPONSES IN CATTLE INFECTED WITH OR VACCINATED AGAINST ANAPLASMA-MARGINALE

An assay was developed for measurement of the peripheral blood lymphoc yte proliferative response (PBLPR) in cattle infected with or immunise d against Anaplasma marginale. PBLPR was not evident in all cattle tha t had recovered from A. marginale infection. However, A. marginale-sen sitised lymphocytes were detected in the spleens of all immune cattle tested in the absence of detectable PBLPR. During the course of initia l infection, cattle exhibited detectable PBLPR for a period correspond ing with and up to 2 weeks after patent parasitaemia, followed by a se cond, usually larger peak in PBLPR corresponding to the time of sub-cl inical relapse of cattle. Analysis of the PBLPR of A. marginale chroni cally infected cattle demonstrated highly variable PBLPR be tween indi viduals and over time. A positive PBLPR was induced in cattle by vacci nation using a crude A. marginale antigen preparation. The PBLPR of va ccinated cattle subsequently infected with A. marginale was markedly d ifferent from that of naive cattle, with reduced PBLPR being associate d with the onset of parasitaemia. The antigen used in the PBLPR assay was inactivated by proteolysis. Proteolysis also abolished immunity th at had been induced in cattle vaccinated using the antigen preparation . A. marginale-sensitised PBL did not proliferate in response to antig en from the heterologous species A. centrale. A. centrale-sensitised P BL, however, responded to A. marginale antigen. Interferon-gamma (IFN- gamma) was detected in PBLPR-assay supernatants and was associated wit h a strong PBLPR.