No serological evidence for a role of HHV-6 infection in chronic fatigue syndrome

Abstract

Human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B) are associated with a variety of conditions including rash, fever, and encephalitis and may play a role in several neurological diseases. Here luciferase immunoprecipitation systems (LIPS) was used to develop HHV-6 serologic diagnostic tests using antigens encoded by the U11 gene from HHV-6A (p100) and HHV-6B (p101). Analysis of the antibody responses against Renilla luciferase fusions with different HHV-6B p101 fragments identified an antigenic fragment (amino acids 389 to 858) that demonstrated ~86% seropositivity in serum samples from healthy US blood donors. Additional experiments detected a HHV-6A antigenic fragment (amino acids 751-870) that showed ~48% antibody seropositivity in samples from Mali, Africa, a known HHV-6A endemic region. In contrast to the high levels of HHV-6A immunoreactivity seen in the African samples, testing of US blood donors with the HHV-6A p100 antigenic fragment revealed little immunoreactivity. To potentially explore the role of HHV-6 infection in human disease, a blinded cohort of controls (n=59) and chronic fatigue syndrome (CFS) patients (n=72) from the US was examined for serum antibodies. While only a few of the controls and CFS patients showed high level immunoreactivity with HHV-6A, a majority of both the controls and CFS patients showed significant immunoreactivity with HHV-6B. However, no statistically significant differences in antibody levels or frequency of HHV-6A or HHV-6B infection were detected between the controls and CFS patients. These findings highlight the utility of LIPS for exploring the seroepidemiology of HHV-6A and HHV-6B infection, but suggest that these viruses are unlikely to play a role in the pathogenesis of CFS.

Keywords: Chronic Fatigue Syndrome (CFS); Human Herpes Virus-6 (HHV6); luciferase immunoprecipitation systems (LIPS).

Figure 1

Detection of anti-p101 HHV-6 antibody responses in healthy US blood donors. (A) Diagrammatic representation of the five different protein fragments from the p101 protein of HHV-6B tested by LIPS (B) Heat map representation of antibody responses to the five different p101 HHV-6B protein fragments in 22 healthy US blood donors. Antibody levels were transformed to fold above buffer blank and then color coded as indicated by the scale. Each individual row represents the antibody level in a single serum sample tested with the different fragments.

Figure 2

HHV-6A and HHV-6B antibody titers in African samples. (A) Scatter plot representation of antibody titers detected by LIPS against the most immunoreactive HHV-6A protein fragment, p100-Δ5, and the HHV-6B p101 protein in African samples. Each circle or square symbol represents average of at least two independent experiments in each individual sample. The dashed line represents the mean plus 10 standard deviations of buffer blanks as cut-off point. (B) Heat map representation of antibody responses of African samples to HHV-6A p100-Δ5 and HHV-6B p100-Δ2. Antibody levels were transformed to fold over buffer blank then color coded as indicated by the scale at right.

Figure 3

LIPS immunoreactivity detection against the HHV-6B p100 and HHV-6A p100 in US samples. Each circle or square symbol represents antibody levels in individual US samples. The dashed line represents the cut-off level for determining seropositivity. As shown, little immunoreactivity was detected by LIPS with the p101 HHV-6A.

Figure 4

LIPS detection of antibodies to HHV-6A p100 (A) and HHV-6B p101 (B) in blood donor control subjects (n=59) and patients with chronic fatigue syndrome (n=72). Each circle or square symbol represents individual sample. The dashed line represents the cut-off level for determining seropositivity.