HIV-1 is not sensitive to blood exosomes. (A) TZM-bl cells were evaluated for cellular uptake of green fluorochrome-labelled blood serum exosome (BE) by FACS. PKH67Green-labelled PBS (gray histogram) was used as control. (B) PCR analysis of host restriction factor (HRF) mRNA present in BE donor samples. Numbers 1 to 4 represent different donors. GAPDH is present in BE and was used as loading control. (C) TZM-bl indicator cells challenged with HIV-1NL4-3 pre-incubated with PBS or with 100 μg/ml donor (n =3) BE. Infectivity was determined by luminescence output with control set at 100% infection. (D) TZM-bl cells exposed to R5- and X4-tropic lab-adapted HIV-1 isolates, including R5-monotropic clade B (SF162), X4-monotropic clade B (IIIB and U1) pre-incubated with PBS or BE. Infectivity was assessed by luminescence expression. Vehicle infectivity was set at 100%. (E) TZM-bl cells exposed to transmitted founder (T/F) molecular infectious clones (REJO and CH162) of HIV-1 pre-incubated with PBS or BE were examined for infectivity by luminescence output. Differences between treatments were not significant (ns). Experiments were repeated at least three times with similar results.