Equid herpesvirus-induced immunosuppression is associated with lymphoid cells and not soluble circulating factors

A paresis isolate of equid herpesvirus 1 (EHV1, Ab4/8) and a plaque-purifie d virus derived from it (EHV1, Ab4/13), induced long-term suppression of bo th mitogenic and antigen-specific lymphocyte proliferations in adult outbre d ponies, Peripheral blood mononuclear cells (PBMC) taken from a pony after EHV1 infection suppressed the in vitro function of normal cells but serum did not. This showed that the observed immune suppression was associated wi th circulating PBMC and/or their products rather than circulating soluble f actors such as antigen or immune complexes. The results suggested that prod uctive infection of lymphocytes by EHV1 was unlikely to result in the obser ved in vitro effects. Moreover, prostaglandin release from monocytes was no t likely to have caused the observed suppression, because lymphocyte respon siveness was not restored in the presence of indomethacin.