Objective: IL-15 has been postulated to play an important role in HIV-1 infection, yet there are conflicting reports regarding its expression levels in these patients. We sought to measure the level of IL-15 in a large, well characterised cohort of HIV-1 infected patients and correlate this with well known markers of inflammation, including CRP, D-dimer, sCD163 and sCD14.
Design and methods: IL-15 levels were measured in 501 people (460 patients with HIV-1 infection and 41 uninfected controls). The HIV-1 infected patients were divided into 4 groups based on viral load: <50 copies/ml, 51-10,000 copies/ml, 10,001-100,000 copies/ml and >100,000 copies/ml. The Mann Whitney test (non-parametric) was used to identify significant relationships between different patient groups.
Results: IL-15 levels were significantly higher in patients with viral loads >100,000 copies/ml (3.02 ± 1.53 pg/ml) compared to both uninfected controls (1.69 ± 0.37 pg/ml, p<0.001) or patients with a viral load <50 copies/ml (1.59 ± 0.40 pg/ml (p<0.001). There was a significant correlation between HIV-1 viremia and IL-15 levels (Spearman r = 0.54, p<0.001) and between CD4+ T cell counts and IL-15 levels (Spearman r = -0.56, p<0.001).
Conclusions: IL-15 levels are significantly elevated in HIV-1 infected patients with viral loads >100,000 copies/ml compared to uninfected controls, with a significant direct correlation noted between IL-15 and HIV-1 viremia and an inverse correlation between IL-15 levels and CD4+ T cell counts. These data support a potential role for IL-15 in the pathogenesis of HIV-associated immune activation.