Background:  Chemokine ligand 3-like 1 (CCL3L1), as a member of the chemokine family, is encoded by a variable copy-number gene and plays an important role HIV-1/AIDS susceptibility. Individuals with more copies of CCL3L1 than their population median have been found to be less susceptible to HIV infection. We investigated whether lower CCL3L1 gene copy number than population median is associated with HIV-1 infection among intravenous drug users (IDU).

Methods:  Blood samples were collected from 385 Caucasian IDU (mean age 26 years). Of these 219 were HIV⁺ (all ART-naive); 282 hepatitis C virus (HCV)⁺; both infections were seen in 175 subjects. The CCL3L1 gene copy-number was measured by real-time polymerase chain reaction (PCR) using primers as described elsewhere and confirmed at 2 copies per diploid genome for each sample.

Results:  In HIV⁺ and HIV^– subjects the CCL3L1 copy numbers ranged between 0 and 5 and 0 and 6, respectively, with the median value of 2 in both populations. More HIV⁺ (86%) or those co-infected with HCV (88%) had 0 to 2 CCL3L1 gene copies than HIV^– (73%), HCV mono-infected (67%) or HIV mono-infected (71%) (OR = 2.13 with 95%CI, 1.28 to 3.58 HIV⁺ vs HIV^–; OR = 3.56 with 95%CI, 1.13 to 1.51) HIV⁺/HCV⁺ vs HIV^–/HCV⁺; OR = 3.0 with 95%CI, 1.2 to 7.4 HIV⁺/HCV⁺ vs  HIV⁺/HCV^–). The number of subjects with CCL3L1 copy numbers of 0 to 2 in HCV⁺ and HCV^– population irrespective of HIV status was similar.

Conclusions:  In the high risk IDU population the subjects who display smaller number of copies of CCL3L1 gene than their population median have increased risk of acquiring HIV-1, indicating that this chemokine may play an essential role in protective immunity.