A blunted TH17 cytokine signature in women with mild cognitive impairment: insights from inflammatory profiling of a community-based cohort of older adults

Abstract

People with dementia have an increase in brain inflammation, caused in part by innate and adaptive immune cells. However, it remains unknown whether dementia-associated diseases alter neuro-immune reflex arcs to impact the systemic immune system. We examined peripheral immune cells from a community-based cohort of older adults to test if systemic inflammatory cytokine signatures associated with early stages of cognitive impairment. Human peripheral blood mononuclear cells were cultured with monocyte or T-cell-targeted stimuli, and multiplex assays quantitated cytokines in the conditioned media. Following T-cell-targeted stimulation, cells from women with cognitive impairment produced lower amounts of T_H17 cytokines compared with cells from cognitively healthy women, while myeloid-targeted stimuli elicited similar amounts of cytokines from cells of both groups. This T_H17 signature correlated with the proportion of circulating CD4+ and CD8+ T cells and plasma glial fibrillary acidic protein and neurofilament light concentrations. These results suggest that decreases in T_H17 cytokines could be an early systemic change in women at risk for developing dementia. Amelioration of T_H17s cytokines in early cognitive impairment could, in part, explain the compromised ability of older adults to respond to vaccines or defend against infection.

Keywords: Alzheimer’s disease; biomarker; immunity; neuroimmunology; sex differences.

Graphical Abstract

Figure 1

T_H17 cytokines from αCD3/αCD28-stimulated PBMC associate with cognitive impairment in women. (A) PBMCs were stimulated with LPS or αCD3/αCD28. Study participants were divided into healthy controls (CDR = 0) or cognitively impaired (CDR = 0.5–1). (B) Cognitive status had no effect on levels of cytokines produced by the LPS-stimulated PBMCs. The cytokines produced by αCD3/αCD28-stimulated PBMCs were clustered into functional categories, including (C) cytokines that promote growth and survival of T cells; (D) T_H1-type cytokines that promote cellular immune and inflammatory responses to infection and injury, (E) T_H2-type cytokines associated with allergy and anti-inflammatory activity; (F) IL-27 associated with polarization of T cells from T_H1/T_H2 to a T_H17 response; and (G) T_H17 cytokines associated with activating cellular immunity and autoimmune disease. (H) The T_H17 cytokines (IL-17A, IL-17F, IL-21, IL-22, CCL20) were standardized and the average z-score was used to identify a T_H17 signature. Cognitively impaired women had a lower T_H17 signature than control women. Circles represent individual study participants. *FDR < 0.05, **FDR < 0.01, ***FDR < 0.001 for unadjusted t-test. See Supplemental Tables 4 and 5 for all statistical comparisons. Multiple comparisons corrected with the Benjamini–Hochberg FDR.

Figure 2

The association of age, apoE genotype, and CVD risk factors with cytokine production from stimulated PBMCs. (A) Increased age correlated with lower amounts of cytokines produced from αCD3/αCD28-stimulated PBMCs. The correlation was gender-dependent, particularly with the T_H17-associated cytokines, where age correlated with lower cytokines in men but not women. (B) In men, ApoE4 carriers (one or two copies) had higher IL-1β, TNFα, and CCL20 from LPS-stimulated PBMCs compared with the E4− group. In women, stimulated E4+ PBMCs produced fewer cytokines (IFNγ, LTα, IL-22, and CCL20) than stimulated E4− PBMCs. Age was not different between the E4− or E4+ groups (t = −1.01, P = 0.32). (C) In men, a greater burden of CVD risk factors (2–3 versus 0–1) was associated with more cytokines produced from αCD3/αCD28-stimulated PBMCs. Women did not show the same pattern. Circles are individual participants. The dashed line shows the 95% confidence interval for the linear regression (A). *FDR < 0.05, **FDR < 0.01, ***FDR < 0.001, unadjusted t-test results (B and C). See Supplemental Tables 7–10 for all statistical comparisons. The Benjamini–Hochberg adjustment used for FDR values.

Figure 3

PBMCs from cognitively impaired subjects make lower amounts of T_H17-associated cytokines than cognitively unimpaired subjects. (A) Individuals with cognitive impairment on the MMSE (score <25) had a low T_H17 signature (mean Z-score of IL-17A, IL-17F, IL-21, IL-22, CCL20) compared with those within a normal MMSE range (score ≥25) (****P < 0.0001; corrected for age and education). (B) The MoCA correlated with the T_H17 signature (age and education adjusted). The dashed line shows the 95% confidence interval for the linear regression. (C) Staging for dementia was based on CDR and MMSE results. The T_H17 signature was lower in women with MCI and mild dementia. In men, the lower T_H17 signature was only seen in individuals with mild dementia. When including both genders, the decline in the T_H17 signature was only seen with mild dementia and not MCI (*P < 0.05, **P < 0.01, ***P < 0.001, Tukey test). (D) The neuropsychological consensus diagnosis for the visit when PBMCs were collected also showed a significant association of a lower T_H17 signature with dementia (*P < 0.05, Tukey test). Markers are individual participants. Statistical tests used: (A) t-test, (B) linear regression, (C and D) one-way ANOVA with Tukey post hoc test.

Figure 4

The T_H17 cytokine signature correlates with fluid biomarkers of neuronal injury and neuroinflammation. Plasma biomarkers, measured by Simoa assays, were correlated with the T_H17 cytokine signature (mean z-score of IL-17A, IL-17F, IL-21, IL-22, CCL20) of the αCD3/αCD28 Dynabead-stimulated PBMCs. Aβ42/40 ratio (A) and p-tau¹⁸¹ (B) levels in plasma did not correlate with the T_H17 cytokine signature. NF-L (C) and GFAP (D) were negatively correlated with the T_H17 cytokine signature. Open circles are male participants. Closed diamonds are female participants. The dashed line shows 95% confidence interval for the linear regression. FDR values are for the unadjusted analysis. See also Supplemental Table 13.

Figure 5

Steady-state plasma cytokine levels fail to detect a dementia-associated immune signature. (A) Cytokine levels were measured in plasma. There was no effect of cognitive impairment status on T_H1 (B) or T_H17 (C) cytokine levels in the plasma. A mean z-score (D) of the four T_H17 cytokines measured in the plasma (C) did not define a dementia-associated immune signature. See also Supplemental Table 14. The plasma cytokine levels did not correlate with cytokines produced by LPS (E) or αCD3/αCD28 Dynabead (F) stimulated PBMCs. The dashed line shows 95% confidence interval for the linear regression. P-values are uncorrected. Markers are individual participants. FDR values are for the unadjusted analysis. See also Supplemental Table 15. Statistical tests used: (A–D) t-test, (E and F) linear regression. Multiple comparisons adjusted using the Benjamini–Hochberg FDR.

Figure 6

The frequency of CD4+ T cells correlates with T_H17 cytokine signature. (A) Gating strategy and (B) representative example of CD4+ and CD8+ T-cell populations in the experimental groups. (C) A significant decrease in the percentage CD3+ CD4+ and CD4+/CD8+ ratio was found in women with cognitive decline compared with control women (FDR < 0.05, see also Supplemental Table 16). (D) The TH17 signature from stimulated PBMCs correlated with the percentage of T cells in the unstimulated PBMCs. Statistical tests used: (C) t-test and (D) linear regression.