Widespread Tau-Specific CD4 T Cell Reactivity in the General Population

Abstract

Tau protein is found to be aggregated and hyperphosphorylated (p-tau) in many neurologic disorders, including Parkinson disease (PD) and related parkinsonisms, Alzheimer disease, traumatic brain injury, and even in normal aging. Although not known to produce autoimmune responses, we hypothesized that the appearance of aggregated tau and p-tau with disease could activate the immune system. We thus compared T cell responses to tau and p-tau-derived peptides between PD patients, age-matched healthy controls, and young healthy controls (<35 y old; who are less likely to have high levels of tau aggregates). All groups exhibited CD4+ T cell responses to tau-derived peptides, which were associated with secretion of IFN-γ, IL-5, and/or IL-4. The PD and control participants exhibited a similar magnitude and breadth of responses. Some tau-derived epitopes, consisting of both unmodified and p-tau residues, were more highly represented in PD participants. These results were verified in an independent set of PD and control donors (either age-matched or young controls). Thus, T cells recognizing tau epitopes escape central and peripheral tolerance in relatively high numbers, and the magnitude and nature of these responses are not modulated by age or PD disease.

Copyright © 2019 by The American Association of Immunologists, Inc.

Figures

Figure 1.. Tau autoimmune responses are detected throughout the protein sequence.

a-c, Magnitude of responses expressed as average SFC (dark blue: proportion IFNγ and red, green or light blue colored bar: proportion IL-5 responses) per 106 PBMCs per peptide. The X-axis indicates the start position of peptide along the tau protein sequence. Left, response to individual overlapping non-modified 16-mer peptides. Right, responses against modified 16-mer peptides. Limit of detection is 100 SFC per 106 PBMCs. a, Patients with Parkinson’s disease (PD: n=22); b, Age-matched healthy controls (HCam: n=21); c, Healthy controls below 35 years of age (HC35: n=21). d, Total magnitude of response (sum of IFNγ and IL-5 responses) per donor, PD (n=22), HCam (n=21), HC35 (n=21). One-tailed Mann-Whitney test, two-tailed Mann-Whitney comparing HCam vs. HC35. Median ± interquartile range is indicated.

Figure 2.. Cytokine profiles of tau-specific responses.

After eliminating non-lymphocytes and doublet cells by forward and side-scatter T cells were gated based on CD3 expression. Boolean gating was used to define cytokine-producing (IFNγ, IL-4, IL-10 or IL-17) cells expressing CD4 and/or CD8. a, Percentage of total cytokine detected from CD3+ T cells in response to tau peptides. Each dot represents one participant (PD, red circles, n=5; HCam, green squares, n=5; HC35, blue triangles, n=9). Median ± interquartile range is indicated. Dotted line indicates 0.05% cut-off for specific cytokine production by CD3+ T cells. b, c, Each point represents one participant that exceeded the cut-off (PD, red circles, n=4; HCam, green squares, n=4; HC35, blue triangles, n=6). Median ± interquartile range is indicated. b, Percentage of responding T cells that produce each cytokine, IFNγ, IL-4, IL-10 and IL-17. c, Percentage of responding T cells that are CD4+, CD8+, CD4−CD8−, or CD4+CD8+.

Figure 3.. Breadth and magnitude of tau-epitope specific responses.

a, Total number of tau-epitopes recognized in the three cohorts, PD (n=22), HCam (n=21), HC35 (n=21). One-tailed Mann-Whitney test. Dotted line indicates cut-off at 10 epitopes. Median ± interquartile range is indicated. b, Average magnitude of response (sum of IFNγ and IL-5 responses) per donor and tau-epitope eliciting a positive response, PD (n=48 epitopes), HCam (n=34), HC35 (n=27). One-tailed Mann-Whitney. Median ± interquartile range is indicated.

Figure 4.. Predicted HLA class II binding for dominant tau epitopes.

Peptide promiscuity based on predicted HLA class II binding for immunodominant epitopes (n=27; black circles) and non-dominant epitopes (n=42; non-epitopes, white circles) derived from tau. X-axis indicates number of HLA class II alleles bound and y-axis indicates the cumulative percentage of peptides that are predicted to bind the number of HLA class II alleles.

Figure 5.. Higher response-frequency and magnitude of tau-specific responses.

a, Total magnitude of response (sum of IFNγ and IL-5 responses) per PD donor (n=13) tested against tau and α-synuclein. Wilcoxon matched-pairs signed rank test. b, Total magnitude of response (sum of IFNγ and IL-5 responses) per HC35 donor (n=25) tested against tau and albumin. Two-tailed Mann-Whitney test.

Figure 6.. Responses against tau peptide pools in independent cohorts.

Total magnitude of response (sum of IFNγ and IL-5 responses) for tau megapool (a) and a pool of the 19 most immunodominant epitopes (b). a, PD (n=37), HCam (n=39), and HC35 (n=38). b, PD (n=25), HCam (n=24), and HC35 (n=19) Two-tailed Mann-Whitney test. Red circles, PD; Green squares, HCam and Blue triangles, HC35. Median ± interquartile range is indicated. c, Percentage IFNγ of total tau response per donor. PD (n=57), HCam (n=57) and HC35 (n=59). † indicates one sample t test for IFNγ polarization more than 50%. Two-tailed Mann-Whitney test for comparison between cohorts. Median ± interquartile range is indicated.