Co-expression of CD4 and CD8 associated with elevated interleukin-4 in a cord T cell line derived by cocultivating normal cord leukocytes and an HTLV-II-producing simian leukocyte cell line (Si-IIA)

A new interleukin-2(IL-2)-dependent T cell line, designated CS-IIA, was established by cocultivating normal human cord leukocytes and a lethally X-irradiated HTLV-II-producing simian leukocyte cell line (Si-IIA). CS-IIA showed CD4 dominance during the early culture. However, after addition of IL-2, CS-IIA predominantly co-expressed CD4 and CD8 (69.5%) and also expressed the surface markers CD1^–, CD3⁺, CD19^–, CD25⁺ and HLA-DR⁺. A significantly elevated level of IL-4 (1697 pg/ml) was observed in the culture supernatant from CS-IIA. In addition, the conversion of phenotype from some CD4⁺CD8⁺ cells to CD4⁺CD8^– was demonstrated by the neutralization assay using anti-IL-4 antibody. CS-IIA had a normal human karyotype and was free from Epstein-Barr virus nuclear antigen and immunoreactive with sera of HTLV-I- or HTLV-II-infected patients and anti-HTLV-1, p19 or p24 mAb. The provirus genome of HTLV-II was detected in this cell line by the polymerase chain reaction combined with a digoxigenin-enzyme-linked immunosorbent assay. However, electron microscopy of CS-IIA cells revealed no C-type virus particles in the extracellular space. These results indicate that HTLV-II can be transmitted from an HTLV-II-infected simian leukocyte cell line to human cord T lymphocytes and suggest that co-expression of CD4 and CD8 on T cells may be induced by the high level of IL-4, which can mediate CD8 induction on CD4⁺ T cell clones.