Anti-CMV IgG Seropositivity is Associated with Plasma Biomarker Evidence of Amyloid-β Accumulation

INTRODUCTION

A growing body of literature suggests that common viral infections may increase the risk of late-life dementias [1]. In particular, some studies suggest that infection with herpes family viruses may be a risk factor for Alzheimer’s disease and related dementias (ADRD) [2, 3]. The herpes virus family comprises eight viruses that are endemic to humans, each of which can establish lifelong reservoirs of latently infected cells. Additionally, emerging evidence also suggests that amyloid-β (Aβ), whose aggregation initiates the pathologic cascade leading to Alzheimer’s disease (AD), may function as an antimicrobial peptide in the innate immune response against viral infection, including herpes viruses [4, 5]. Chronic infection with herpesviruses may therefore contribute to ADRD risk through its effects on Aβ metabolism.

The strongest evidence for an association of herpesvirus infections with incident dementia and its prodrome, mild cognitive impairment, is with the alpha herpesviruses: herpes simplex virus (HSV)-1, HSV-2, and varicella zoster virus (VZV) [2, 6]. There is less evidence for cytomegalovirus (CMV), a member of the beta herpesvirus family [7, 8]. CMV is endemic, with adult seroprevalence estimated at 83% globally and at 48% in the United States [9, 10]. CMV primarily infects myeloid cells, including monocytes; however, all resident cells of the central nervous system (CNS), including microglia and astrocytes, are susceptible to CMV infection [11, 12].

A 2019 systematic review and meta-analysis failed to identify an association of prior CMV infection with incident dementia or mild cognitive impairment [2]. Relatively few studies have evaluated associations of measures of CMV seropositivity with biomarkers of ADRD pathology [7, 13]. One study evaluated associations of plasma Aβ with anti-CMV Immunoglobulin G (IgG) in individuals with AD and healthy controls. This study found no significant association between measures of CMV seropositivity and Aβ pathology, however the study’s methodology for plasma Aβ quantification may not have been sufficiently sensitive for comprehensive detection of Aβ levels [8].

To our knowledge, no studies have evaluated the association of anti-CMV IgG with plasma biomarkers of ADRD risk in middle-aged adults using ultrasensitive assay methodologies. The objective of this analysis was to determine, in a sample of young and middle-aged adults recruited for an exercise study, the cross-sectional associations among measures of CMV seropositivity with plasma biomarkers of ADRD risk, including Aβ (the ratio of Aβ₄₂/Aβ₄₀ with a lesser ratio reflecting greater risk of CNS Aβ accumulation), neurofilament light (NfL, a marker of axonal neurodegeneration) and glial fibrillary acidic protein (GFAP, a marker of neuroinflammation).

METHODS

RESULTS

Association of anti-CMV IgG with plasma ADRD biomarkers

We first evaluated whether CMV seropositivity was associated with the plasma ADRD biomarkers. CMV seropositivity was associated with a lesser plasma Aβ₄₂/Aβ₄₀ ratio, adjusting for age, sex, and race (Table 2). There were no significant associations of CMV seropositivity with plasma log-NfL or log-GFAP (all p≥0.622). We next evaluated associations of anti-CMV IgG levels with the plasma Aβ₄₂/Aβ₄₀ ratio, excluding participants who were CMV seronegative. In CMV seropositive participants, greater anti-CMV IgG levels were associated with a lesser Aβ₄₂/Aβ₄₀ ratio, adjusting for age, sex, and race (Table 3). Adjusting for log-CRP did not affect our findings (data not shown). To determine whether associations of anti-CMV IgG levels with the Aβ₄₂/Aβ₄₀ ratio differed by age, sex, or race in CMV seropositive participants, we refitted models with an interaction term. There was no evidence that associations were significantly moderated by age (p = 0.086), sex (p = 0.501), or race (p = 0.931). Scatter plots showing associations of anti-CMV IgG levels with the plasma ADRD biomarkers in CMV seropositive participants are shown in Fig. 1.

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Table 2

Association of CMV Seropositivity with the Plasma ADRD Biomarkers. Univariate linear

	Aβ42/Aβ40 Ratio			GFAP			NfL
	Beta	95% CI	p	Beta	95% CI	p	Beta	95% CI	p
Age	–2.49e–04	–4.07e–04, –9.07e–05	0.002	2.37e–02	1.92e–02, 2.82e–02	<0.001	3.06e–02	2.65e–02, 3.47e–02	<0.001
Sex
Female	—	—		—	—		—	—
Male	–5.07e–04	–3.45e–03, 2.44e–03	0.735	–1.99e–01	–2.83e–01, –1.15e–01	<0.001	–5.97e–02	–1.36e–01, 1.68e–02	0.126
Race
Not African American	—	—		—	—		—	—
African American	2.19e–04	–4.03e–03, 4.47e–03	0.919	–4.33e–02	–1.64e–01, 7.75e–02	0.481	–1.49e–01	–2.59e–01, –3.81e–02	0.009
CMV Carrier Status
CMV Seronegative	—	—		—	—		—	—
CMV Seropositive	–3.02e–03	–5.97e–03, –7.18e–05	0.045	2.08e–02	–6.30e–02, 1.05e–01	0.625	1.26e–02	–6.41e–02, 8.92e–02	0.747

CI, confidence interval; NfL, neurofilament light; GFAP, glial fibrillary acidic protein.

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Table 3

Association of Anti-CMV IgG Levels with the Plasma

	Aβ42/Aβ40 Ratio
	Beta	95% CI	p
Age	–2.68e–04	–4.98e–04, –3.90e–05	0.022
Sex
Female	—	—
Male	–5.85e–04	–5.05e–03, 3.88e–03	0.796
Race
Not African American	—	—
African American	–4.20e–04	–5.86e–03, 5.02e–03	0.879
Anti–CMV IgG Levels	–4.85e–05	–8.45e–05, –1.25e–05	0.009

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Fig. 1

Association of anti-CMV IgG levels with the plasma ADRD biomarkers in CMV seropositive participants. Scatterplot showing the association of anti-CMV IgG levels (EU/mL) with the plasma Aβ₄₂/Aβ₄₀ ratio in CMV seropositive participants. Pearson correlation coefficient and corresponding p-value are shown.

DISCUSSION

To our knowledge, this is the first study to evaluate associations between anti-CMV IgG levels and ultrasensitive plasma measures of ADRD pathology. Here, in a sample of mostly middle-aged adults recruited for an exercise intervention, anti-CMV IgG levels were not associated with plasma GFAP or NfL. However, in CMV seropositive participants, anti-CMV IgG levels were associated with a lesser plasma Aβ₄₂/Aβ₄₀ ratio. This association may be direct and causally related to CMV neuro-cytotoxicity, indirect and mediated by inflammatory factors resulting from CMV infection burden and/or the immune response, or a combination of direct and indirect factors.

The inverse association between anti-CMV IgG levels and plasma Aβ₄₂/Aβ₄₀ may result from an endogenous protective response to CMV infection. This association is consistent with work in animal and in vitro AD models indicating human Aβ-amyloidosis serves as a protective response against herpesvirus infection [4]. Aβ is upregulated by pattern- and damage-associated molecular patterns (PAMPs/DAMPs), likely functioning as a cytokine in the innate immune response [17]. CMV may induce CNS Aβ production, CNS Aβ accumulation, and plasma Aβ₄₂/Aβ₄₀ reduction. Also, the immune response to CMV viral activity could induce peripheral Aβ production [17] from the adrenal gland, kidney, heart, liver, and various peripheral cell types including thrombocytes and endothelial cells [18]. Increases in peripheral Aβ could lead to increased CNS Aβ and CNS Aβ aggregation while reducing Aβ₄₂/Aβ₄₀ [18]. To our knowledge, as compared to HSV-1, HHV-6, and HHV-7, there is no evidence of CNS CMV infection in post-mortem human AD brain tissue [19–21]. Thus, it is possible that in the CNS, periphery, or both, CMV induces an immune response that produces Aβ and resolves CNS CMV infection; however, residual accumulation leads to ADRD development without post-mortem evidence of prior CMV infection.

Our findings are consistent with human population studies showing ADRD associations with clinical diagnoses of herpesvirus infections generally, and CMV specifically. Based on data from the FinnGen and UK biobanks [1], risk of dementia is increased after diagnosis of herpes and other viral infection, with greatest risk in the initial year following infection. However, in this study, over time, the increased risk of dementia was attenuated, suggesting these findings were impacted by an observation bias whereby recently infected individuals have greater healthcare exposure and a greater likelihood of dementia diagnosis. Also, a greater 10-year risk of developing AD is associated with the combination of CMV and HSV-1 infection [22], implying a potential synergistic effect of multiple herpesvirus infections. Consistent with CMV-specific contributions to ADRD pathology, an increased risk of dementia is associated with a prior history of CMV-associated end-organ disease [23].

Our findings are also consistent with connections between herpesvirus infections and ADRD pathology measures including brain imaging, cognitive performance, and ADRD biomarkers. In data from the Baltimore Longitudinal Study of Aging, a clinical diagnosis of varicella-zoster, HSV-1, or HSV-2 is associated with longitudinal CNS white matter volume decline, accelerated declines in attention, and elevated plasma GFAP; furthermore, treatment with antivirals attenuate declines in occipital white matter [24]. However, herpesvirus-related diagnoses were not associated with plasma Aβ₄₂/Aβ₄₀ ratio or NfL.

In contrast to clinical diagnoses of herpes or CMV infection, seropositivity and antibody concentrations are less consistently related to dementia [2, 25], cognitive performance [26–28], or plasma Aβ [8], consistent with our work. Further, CMV antibody concentrations may reflect successful endogenous Aβ responses to CMV infection, reducing the likelihood of clinical CMV infection, dementia, or cognitive impairment diagnoses.

CMV infection and the response to infection is very likely to be one of many factors including genetics and cardiometabolic risk factors that contributes to Aβ production, CNS Aβ aggregation, and eventual development of CNS Aβ amyloidosis, tau pathology, and dementia. These multiple etiologies for ADRD explain, in part, that in the general population, the plasma Aβ₄₂/Aβ₄₀ ratio is poorly predictive of future dementia risk [29], and significant CNS Aβ accumulation without tau pathology or cognitive impairment occurs in up to 25% of cognitively unimpaired older adults [30].

Future studies are required to determine whether CMV seropositivity is associated with gold standard assessments of CNS Aβ-amyloidosis using CSF or Aβ PET imaging. Additionally, longitudinal studies are required to determine whether anti-CMV IgG levels predict future CNS Aβ-amyloidosis. If CMV infection is associated with future CNS Aβ-amyloidosis, the next step would be to determine whether anti-CMV antivirals can delay or prevent CNS Aβ-amyloidosis in high-risk individuals. There is currently a clinical trial underway evaluating high dose valacyclovir—an anti-viral medication with efficacy against HSV-1, HSV-2, VZV, and CMV—in mild AD dementia [31].

AUTHOR CONTRIBUTIONS

Daniel Parker (Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Visualization; Writing – original draft; Writing – review & editing); Heather E. Whitson (Writing – review & editing); Patrick J. Smith (Writing – review & editing); Virginia B. Kraus, MD, PhD (Writing – review & editing); Janet L. Huebner (Investigation; Methodology; Writing – review & editing); Rebecca North (Methodology; Writing – review & editing); William E. Kraus (Funding acquisition; Investigation; Resources; Writing – review & editing); Harvey Jay Cohen (Writing – review & editing); Kim M. Huffman (Writing – review & editing).