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Tilorone and Poly rI:rC, in the presence of DEAE-dextran, were found to exhibit a marked synergism with respect to the induction of interferon in L929 and primary mouse embryo fibroblasts, but not human foreskin fibroblasts, in cell cultures. The degree of synergism was proportional to the concentrations of tilorone and Poly rI:rC and was influenced by the times of addition of the compounds relative to each other.

Nude athymic mice, which lack T-lymphocytes and are unable to mount a cellular immune response, failed to develop the lymphopenia so characteristically produced by a 100 mg/kg oral dose of tilorone hydrochloride in normal mice. The antiviral activity detected in athymic mice 18 hr after a 150 mg/kg oral dose of tilorone was significant, although somewhat less than that found in treated normal mice. These findings suggest that tilorone hydrochloride has a specific effect on T-lymphocytes that accounts for its effect on cellular immunity, but that its antiviral activity is not primarily mediated by T-lymphocytes.

Biological, biochemical, and biophysical properties of three lymphocytic choriomeningitis (LCM) virus strains were compared. The biological property examined was the concentration range of virus which would, when injected into neonates, cause a carrier state. The dosage range for the CA1371 and Traub strains was found to be as broad as the limits examined (5 to 100 ld(50) units/mouse). The WCP strain, however, would only produce carriers within a 3 to 5 ld(50) range. The biochemical properties examined were the growth rates in tissue culture and the effect of varying the input ratio of virus to cells. With identical input ratios, the Traub strain reached a peak titer 32 hr after infection. The CA1371 and WCP strain reached their peaks at the 40th hr. With a 10-fold decrease in the amount of CA1371 virus per cell, peak titer (as high as in the above experiments) was not obtained until 56 hr postinfection. The biophysical properties examined were stability in density gradients and inactivation rates at 4C. In potassium tartrate gradients, full recovery of the CA1371 and WCP strain could be achieved. However, inactivation kinetics showed that only the CA1371 strain was much more stable than the Traub-LCM. The realization that marked differences in LCM strains exist is discussed in relation to certain inconsistencies in the literature.