Comparative analysis of CD1 d-restricted natural killer T cells in people who inject drugs with chronic or spontaneously resolved hepatitis C

Background: Natural killer T (NKT) cells represent a subset of immune cells that share characteristics of innate and adaptive immunity. Invariant NKT cells recognize glycolipid antigens such as α galactosylceramide (αGalCer) presented by the non classical MHC molecule CD1 d. Decreased NKT cell frequencies have been reported in chronically HCV infected patients, however, contradicting reports exist. We therefore aimed to comparatively study NKT cell frequencies and function in people with chronic and spontaneously resolved HCV infection. Methods: CD1 d-restricted NKT (CD1 d NKT) cells of chronically HCV infected people who inject drugs (PWID) (n = 28) and PWID with resolved HCV infection (n = 33) were analyzed by flow cytometry utilizing a CD1 d-tetramer complexed with αGalCer. Results: CD1 d NKT cell frequencies did not differ between PWID with resolved HCV infection and PWID with chronic HCV infection. Expression of the NK cell receptors NKG2A, NKG2C, NKG2D and KIR2DL3 on CD1 d NKT cells, previously described to be differentially regulated on NK cells in HCV infection, was also not significantly different between groups. Interestingly, CD1 d NKT cells of chronically infected PWID showed significantly higher expression of the activation marker CD38. Despite this activated phenotype in PWID with chronic HCV infection CD1 d NKT cells expressed high levels of CD127 and CD161 and predominantly lacked CD57 irrespective of the infection status. Moreover, no difference in expression of the exhaustion markers PD-1 and BTLA could be observed between groups. Treatment of PBMCs with αGalCer induced robust CD1 d NKT cell expansion in both groups associated with upregulation of CD38 and downregulation of CD127. Independent of HCV status, CD1 d NKT cells produced similar levels of IFNγ, IL 2, TNFα, IL-4 and CD107a. Conclusion: Our data indicate that chronic HCV infection in PWID is associated with increased expression of the activation marker CD38 on CD1 d NKT cells, however, this activated phenotype was not associated with differential functionality or altered expression of other NK cell receptors or T cell differentiation markers. Corresponding author: Timm, Jörg E-Mail: joerg.timm@med.uni-duesseldorf.de