Background:  Although different type I interferons (IFN) appear to vary in their anti-HIV activity, they have not been assessed in the same primary cell type. We hypothesize that different classes of type I IFN can be classified as weak or strong inhibitors of HIV replication in monocyte-derived macrophages (MDM).

Methods:  Monocytes obtained from peripheral blood mononuclear cells (PBMC) derived from healthy donor blood were seeded in wells of 48-well plates at a density which gave rise to 2x10⁵ MDM per well after 5 days of macrophage colony-stimulating factor (MCSF) treatment. MDM were exposed to IFN pretreatments followed by HIV infection for 2 hours at an multiplicity of infection (MOI) of 0.3. IFN were not replaced in the media following washing to remove the virus. The significance of different IFN treatments to be estimated for 6 to 8 replicate wells per condition using a 1-way ANOVA with a Tukey correction. HIV replication was assessed in the cell supernatants by enzyme-linked immunosorbent assay (ELISA) for p24 and by the detection of gag transcripts by quantitative real-time polymerase chain reaction (qRT-PCR).

Results:  Preliminary experiments assessed the length of IFN-a2 pretreatment needed to fully protect MDM from HIV infection. MDM were pretreated with IFN-a2 for 2, 6, 12, and 18 hours prior to HIV infection, and p24 quantities assessed at days 1, 4, 8, and 14 post-infection. p24 levels at day 8 revealed that all lengths of IFN-a2 pretreatment significantly inhibited HIV replication (p <0.01), but that increasing lengths of pretreatment were significantly better (p <0.01) for as long as 12 hours, such that there was no significant difference between 12 and 18 hours of pretreatment. Therefore, a 12-hour pretreatment of MDM was selected to determine the ability of 186 picomolar solutions of different type I IFN (IFN-a1, -a2, and -a7, -b, -t, and -w) to inhibit HIV replication. p24 levels at day 8 post-infection indicated that:  all IFN treatments significantly inhibited HIV replication (p <0.01), all IFN treatments apart from IFN-t were significantly better than IFN-a1 (p <0.01), and  only IFN-a2 and -b were significantly better than IFN-t (p <0.05). This result was replicated when gag transcript levels were measured by qRT-PCR.

Conclusions:  Type I IFN can be classified as weak (IFN-a1 and -t), moderate (IFN-a7 and -w), or strong inhibitors of HIV replication (IFN-a2 and -b). In the future, microarray gene expression analysis will identify interferon-stimulated genes with anti-HIV properties as those that are up-regulated by strong inhibitors, but not by weak or moderate inhibitors or by HIV infection alone.