Effect of heat and fresh human serum on the infectivity of human T-cell lymphotropic virus type III evaluated with new bioassay systems.

MT-4 cells, which are a human T-cell lymphotropic virus type I (HTLV-I)-positive cell line highly permissive to HTLV-III infection, were used to detect the biologically active virus. For quantitation of the virus, induction of HTLV-III-specific antigen(s) and inhibition of DNA synthesis in infected MT-4 cells were assessed by indirect immunofluorescence and by a proliferation assay measuring [3H]thymidine uptake, respectively. HTLV-III was fully inactivated by treatment at 56 degrees C for 30 min. It was not inactivated by treatment with fresh anti-HTLV-III-negative serum. Thus, these assay systems with MT-4 cells would be useful in further studies on acquired immune deficiency syndrome.