Increased expression of CD39 on natural killer cells in patients with chronic hepatitis C is associated with an immature phenotype

Natural killer (NK) cell function has been shown to be crucial in the innate immune response against chronic viral infections such as hepatitis C (HCV) and HIV. The Regulation of NK cells is not dominated by a single receptor as in B or T cells, but the result of an orchestrated interplay of a variety of activating and inhibitory molecules such as C-type lectin and killer cell immunoglobulin receptors. CD39 is an ectonucleotidase which is known for its ability to degrade ATP to AMP and in connection with CD73 to adenosine. Recent findings in chronic viral infections and especially in the liver revealed the importance of this modulatory pathway for dysfunctional CD8+ and regulatory T cell responses.

The aim of this study is to investigate the distribution and expression level of CD39 on different NK cell populations derived from peripheral blood. To furthermore reveal its role in chronic infections such as HIV and HCV, we compared PBMC samples from HCV mono-infected, HCV/HIV co-infected and HIV mono-infected patients to healthy controls.

In a multicolor flow cytometry panel NK cell subsets were characterized by their expression of CD56 and CD16 (otherwise lineage negative) and were analyzed for expression of KIR2D, KIR3DL1/DL2 and CD57 as well as the ectonucleotidases CD39 and CD73.

Overall, the frequency of CD39-positive CD3-CD56+ NK cells was significantly increased in patients with HCV (Mean 8.86% ± 6.43), HCV/HIV (Mean 14.63% ± 10.51) and HIV infection (Mean 23.39% ± 12.22) compared to healthy controls (Mean HC 4.35% ± 3.67, HC vs. HCV p = 0.0097; HC vs. HCV/HIV p = 0.0076; HC vs. HIV p = 0.0041). Furthermore, the CD3-CD56brightCD16 ± NK cell subset shows a relatively higher frequency of CD39-positive cells compared to the CD3-CD56dimCD16 ± NK cell subset within all groups (e.g. HCV Mean: 24.95% ± 11.43 (CD56bright NK) vs. 5.73% ± 5.65 (CD56dim NK), p < 0.0001). Next, we hypothesized that expression of CD39 might be associated with NK cell differentiation. We compared its expression on CD56bright, CD56dimpanKIR-CD57- and CD56dimpanKIR+CD57+ NK cells subsets representative for a previously described maturation pathway. We observed the highest frequency of CD39-positive cells in CD56bright NK cells, followed by a stepwise decline in frequency from CD56dim panKIR-CD57- NK cells to CD56dimpanKIR+CD57+ NK cells within all groups (e.g. HCV Mean: From 26.33% ± 11.85 over 14.22% ± 8.09 to 2.20% ± 3.26; CD56bright vs. CD56dimpanKIR-CD57- p = 0.01; CD56bright vs. CD56dimpanKIR+CD57+ p < 0.0001).

Our data provides evidence that the frequency of CD39-positive NK cells is increased in chronic viral infections like HCV and HIV. The distribution of CD39-positive NK cells shows an association with NK cell maturation. Taken together these results indicate a differentiation-associated skewing of the modulatory function of NK cells mediated via CD39 expression in HCV and HIV compared to healthy controls.

Corresponding author: Dierks, Patrick

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