[The degree of virulence in Far Eastern strains of the tick-borne encephalitis virus].

Screening of immunomodulating properties of 45 tick-borne encephalitis (TBE) virus strains isolated in the southern part of the Soviet Far East was carried out. TBE virus strains were found to have different effects on the immune responsiveness of host splenocytes. Over 90% of the strains isolated from hematothermals could inhibit the immune response of the host to a heterologous antigen (sheep erythrocytes); similar properties were found in 5 strains isolated from ticks. At the same time, most strains isolated from the vectors were unable to modulate the immune response of antibody-producing cells and 3 strains even had immunostimulating properties. The existence of significant correlation (r = -0.57; p < 0.01) between the immunomodulating activity of a strain and peripheral virulence of the virus for white mice indicates that the immunomodulation parameter may be used as another pathogenetic marker. This marker and that of the peripheral activity served the basis for creation, by means of the mathematical method of discrimination analysis, of a new pathogenetic characteristic--a single marker of strain virulence.