The Responses of Normal and Athymic Mice to Infections by Togaviruses: Strain Differentiation in Active and Adoptive Immunization

formerly of The Microbiological Establishment Porton Down, Salisbury, Wilts, U.K. Strains of yellow fever virus (YFV), Venezuelan equine encephalomyelitis virus (VEEV) and Semliki Forest virus (SFV) have been used to compare the stimulations of regulatory immunity (pre-challenge), antibody synthesis and protective immunity (post-challenge) in athymic-nude and normal mice. Similarly, direct assessments have been extended to athymic recipients of normal spleen cells and to adoptively immunized mice. The results indicate that the responses of mice to different togaviruses or strains of togaviruses may be differentially T-lymphocyte dependent at any one or more of the above three stages of host response. T-cell reconstitution or adoptive immunization may be effective only for the virus strains of highest immunogenicity. These results suggest a resolution of T-lymphocyte dependence at three levels of host response to virus infections. This approach may be of value in the similarly direct in vivo differentiation of other virus strains and as a practical framework for the consideration of the in vivo significance of the variety of in vitro lymphocyte markers. * Address for reprint requests: Sutherlands, Pitton, Salisbury SP5 1DZ, Wilts, U.K. Received 14 June 1979; accepted 30 August 1979.