We developed the syncytium induction assay in which peripheral blood lymphocytes from HTLV-I healthy carrier donors were co-cultivated with the human epidermoid cancer cells (ME180).
A significant increase of multinucleated syncytium formation was observed in ME180 cells along with HTLV-I expression after co-cultivation with 1×106 HTLV-I carrier lymphocytes. Co-cultivation with HTLV-I negative lymphocytes did not induce a significant syncytium formation. The syncytium formation activities varied widely among carrier lymphocytes and did not correlate with the expression of HTLV-I antigen in the lymphocytes. By freeze-thawing treatment to lymphocytes this syncytium formation was inhibited.
This syncytium induction assay using ME180 cells can be utilized for detection of infectious HTLV-I in peripheral lymphocytes in healthy carriers and thereby for their follow up study whose natural history is largely unknown.