Independent skewing of the T cell and NK cell compartments associated with cytomegalovirus infection suggests division of labor between innate and adaptive immunity

Abstract

Cytomegalovirus (CMV) infection induces profound changes in different subsets of the cellular immune system. We have previously identified an immune risk profile (IRP) where CMV-associated changes in the T cell compartment, defined as a CD4/CD8 ratio < 1, are associated with increased mortality in elderly people. Since natural killer (NK) cells have an important role in the defense against viral infections, we examined whether the expansion of CD8 + T cells seen in individuals with CD4/CD8 ratio < 1 is coupled to a parallel skewing of the NK cell compartment. A number of 151 subjects were examined with CMV serology and a flow cytometry panel for assessment of T cell and NK cell subsets. CMV-seropositive individuals had higher frequencies of CD57 + and NKG2C + NK cells and lower frequencies of NKG2A + NK cells, in line with a more differentiated NK cell compartment. Intriguingly, however, there was no correlation between CD4/CD8 ratio and NK cell repertoires among CMV-seropositive donors, despite the profound skewing of the T cell compartment in the group with CD4/CD8 ratio < 1. Conversely, donors with profound expansion of NK cells, defined as NKG2C + NK cells with high expression of CD57 and ILT-2, did not display more common changes in their T cell repertoire, suggesting that NK cell expansion is independent of the T cell-defined IRP. Altogether, these results indicate that the effect of CMV on CD8 T cells and NK cells is largely nonoverlapping and independent.

Fig. 1

Identification of T cell and NK cell subsets. Whole blood was stained and analyzed by six-color flow cytometry. The T cells were gated according to the expression of CD3 together with CD4 and CD8, respectively (a). The NK cells were identified as CD3neg CD56pos lymphocytes and then gated according to their expression of NKG2A, NKG2C, ILT-2, and CD57 (b)

Fig. 2

Influence of CMV on the T cell compartment. The subjects were divided into three groups based on CMV seropositivity and CD4/CD8 ratio: CMV- (n = 33), CMV + CD4/CD8 > 1.2 (referred as CD4/CD8 > 1.2, n = 71), and CMV + CD4/CD8 < 1 (referred as CD4/CD8 < 1, n = 47) (a). The CD4/CD8 < 1 group had a lower (p = 0.021) CD4 count than the CMV- and CD4/CD8 > 1.2 groups (b), but the most prominent difference was an increased CD8 count in the CD4/CD8 < 1 group, indicative of CD8 T cell expansion (c). The median value is indicated for every group.

Fig. 3

Normal NK cell repertoires in individuals with an inverted CD4/CD8 ratio. The total number of NK cells and the ratio of CD56^bright/CD56^dim NK cells were similar irrespective of CMV seropositivity and CD4/CD8 ratio of the donors (a–c). CMV-seronegative subjects had higher frequencies of NKG2A + NK cells compared to CMV-seropositive individuals but the levels were similar in individuals with or without an inverted CD4/CD8 ratio (d–e). NKG2C + NK cells were more common in CMV-seropositive individuals, but there was no significant difference according to CD4/CD8 ratio (d–e). The expression of CD57 and ILT-2 showed a large inter-individual variation, but there was no significant difference between individuals with or without an inversed CD4/CD8 ratio (d–e). The median value is indicated for every group

Fig. 4

NK cell expansion and correlation to CD4/CD8 ratio. Representative staining of donors with and without NK cell expansions, defined as high expression of NKG2C + in conjunction with CD57 and/or ILT-2 (a). NK cell expansions were more common in CMV-seropositive donors but independent of CD4/CD8 ratio (b). When combining the T and NK cell analysis, the cohort could be divided into five groups based on CMV serostatus, CD4/CD8 ratio and whether or not the individual had an expanded NK cell subset or not: CMV-seronegative donors (CMV-), CMV-seropositive donors without any visible imprints in their immune repertoire (CMV + CD4/CD8 > 1.2 Exp-), CMV-seropositive donors with only CD8 T cell expansion (CMV + CD4/CD8 < 1 Exp-), CMV-seropositive donors with only NK cell expansion (CMV + CD4/CD8 > 1.2 Exp+) and CMV-seropositive donors with both CD8 T cell and NK cell expansion (CMV + CD4/CD8 < 1 Exp+) (c).

Fig. 5

T cell differentiation status in correlation to NK cell expansion, CD4/CD8 ratio and CMV serostatus. Absolute numbers and frequencies of naive (CCR7 + CD27 + CD28 + CD45RA+), effector memory (CCR7-CD27-CD28-CD45RA-) and TEMRA (CCR7-CD27-CD28-CD45RA+) T cells in the CD8+ (a) and CD4+ (b) compartments correlated with NK cell expansion, an inversed CD4/CD8 ratio and CMV serostatus. An inversed CD4/CD8 ratio was associated with a decrease in naive T cells and an increase in effector memory and TEMRA cells, but generally the number of highly differentiated T cells was independent of NK cell expansion. The median value is indicated for every group