Effect of p12^I mutation on RNA, protein, and infectious virus production in transfected PBMC. (A) RT-PCR of total RNA from ACH- and ACH.p12^I-transfecants, MT-2 (HTLV-1-positive) and Jurkat (HTLV-1-negative) cells. The 232-bp p12^I and constitutive 183-bp ABL transcript products are indicated. (B) p19 antigen detected by ELISA in ACH and ACH.p12^I-transfectant PBMC culture supernatants. Results are expressed as mean pg/mL ± SEM of p19 antigen obtained from 10 independent transfections. (C) HTLV-1 env-mediated syncytia formation in HOS cells by ACH-, ACH.p12^I-, or pKS- (vector control) transfectants, Jurkat (HTLV-1-negative), or HuT102 (HTLV-1-positive) cells. Results are expressed as mean number ± SEM of syncytia (four or more nuclei) per well obtained from 10 wells (five independent transfections); a, b, and c are significantly different, P < .05. Note that HuT102 is a high virus-producing cell line and is expected to induce higher numbers of syncytia compared to the PBMC transfectants. (D) Infectious virus production as measured by p19 antigen production from cultures containing lethally irradiated ACH- or ACH.p12^I-transfectants alone or cocultured with naı̈ve rabbit PBMC. Results are expressed as absorbance values for 1 and 7 day after wash culture supernatants measured by p19 antigen ELISA.