Measles virus inhibits lymphocyte proliferation in vitro by two different mechanisms.

We studied the effect of two different strains of measles virus (MV) on the lymphocyte blast transformation response. Infectious virus inhibited the proliferation response to PHA early during the culture when freshly isolated PBMC were stimulated. However, MV stimulated the proliferation of T cell lines early after infection and the inhibition was a late phenomenon associated with cell death. The early inhibition by the Edmonston strain of MV was shown to be monocyte-dependent by depletion studies with monoclonal antibodies. It could be partially explained by IFN-alpha production as the addition of anti-IFN-alpha antiserum to the cultures reversed the virus-induced inhibition and the addition of IFN reduced the response of uninfected PBMC. The late inhibition by the Edmonston strain was associated neither with monocytes nor with IFN-alpha but correlated with cell death in cultures. The inhibition by the Halle strain of MV was strong and associated with cell death already early after infection. The results demonstrate that MV inhibits lymphocyte proliferation by two different mechanisms and different virus strains vary both in the magnitude and mechanism of inhibition.