INHIBITORY ACTIVITY IN SALIVA OF CELL-TO-CELL TRANSMISSION OF HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE-1 IN-VITRO - EVALUATION OF SALIVA AS AN ALTERNATIVE SOURCE OF TRANSMISSION

Human T-cell lymphotropic virus type 1 (HTLV-1) is known to be transmi tted vertically through breastfeeding and horizontally by blood transf usion and sexual contact, Our intervention study has suggested the pre sence of additional alternative maternal transmission pathways, To exp lore the possibility of transmission through saliva, we used PCR to qu antify the HTLV-1 provirus in saliva samples from 18 carrier mothers a nd 10 patients with HTLV-1-associated myelopathy/tropical spastic para paresis, The provirus was detected in 60 and 90%, respectively, of the samples, with estimated copy numbers in the range of 10 to 10(4)/ml, However, the saliva, regardless of the presence or absence of antibodi es to the virus, showed a strong tendency to inhibit the cell-to-cell transmission of HTLV-1 in vitro, as examined by a syncytium inhibition assay, The natural inhibitory activity in saliva of seronegative volu nteers was heat sensitive, and most of the activity was recovered by u ltrafiltration in the fraction of macromolecules with a molecular weig ht of more than 100,000, In addition to this natural activity, saliva of HTLV-1-infected individuals contained immunoglobulin G molecules ca pable of neutralizing syncytium formation, These results strongly sugg ested that HTLV-1-infected cells in the carriers' saliva, which contai ns neutralizing antibodies in addition to the natural activity inhibit ing cell-to-cell viral infection, barely transmit the virus, Transmiss ion of HTLV-1 through the saliva would thus seem to be rare, if it occ urs at all.