Pathogen or Bystander: Clinical Significance of Detecting Human Herpesvirus 6 in Pediatric Cerebrospinal Fluid.

Human herpesvirus 6 (HHV-6) is an important cause of meningitis and meningoencephalitis. As testing for HHV-6 in cerebrospinal fluid (CSF) is more readily available using the FilmArray Meningitis/Encephalitis panel (FA-ME; BioFire Diagnostics, Salt Lake City, UT), we aimed to determine the clinical significance of detecting HHV-6 in order to identify true infections and to ensure appropriate antiviral initiation. Chart review on 25 patients positive for HHV-6 by FA-ME was performed to determine clinical presentation, comorbidity, treatment, and outcome. The presence of chromosomally integrated HHV-6 (ciHHV-6) DNA was also investigated. Of 1,005 children tested by FA-ME, HHV-6 was detected in 25 (2.5%). Five patients were diagnosed with either HHV-6 meningitis or meningoencephalitis based on HHV-6 detection in CSF, clinical presentation, and radiographic findings. Detection of HHV-6 by FA-ME led to discontinuation of acyclovir within 12.0 h in all 12 patients empirically treated with acyclovir. Six of the 12 patients were started on ganciclovir therapy within 6.8 h; 4 of these were treated specifically for HHV-6 infection, whereas therapy was discontinued in the remaining 2 patients. CSF parameters were not generally predictive of HHV-6 positivity. The presence of ciHHV-6 was confirmed in 3 of 18 patients who could be tested. Five of the 25 patients included in the study were diagnosed with HHV-6 meningitis/meningoencephalitis. FA-ME results led to discontinuation of empirical antiviral treatment in 12 patients and appropriate initiation of ganciclovir in 4 patients. In our institution, detection of HHV-6 using FA-ME led to faster establishment of disease etiology and optimization of antimicrobial therapy.

Interactions between mouse IgG2 antibodies are common and mediated by plasma C1q.

BACKGROUND: The simultaneous use of multiple antibodies for multicolor flow cytometry is increasingly common and presents the opportunity for antibody interactions. METHODS: Antibodies of differing isotypes were evaluated in pair-wise combinations for the presence of antibody interactions, using a standard whole blood lysing method or variations thereof. RESULTS: Artifactual interactions were identified and preferentially involved IgG2a (58%) or IgG2b (33%) antibodies and a single IgG1 antibody (3%). The interactions were present in all 10 random peripheral blood samples evaluated and required only whole blood and the two antibodies. Plasma removal prior to antibody incubation eliminated the interaction, as did switching any single IgG2 antibody to an IgG1 clone. Heat-inactivated plasma eliminated the interactions, and the addition of purified C1q to washed cells was capable of recreating the interaction in its entirety, confirming the mediation by complement C1q. CONCLUSIONS: Complement C1q mediates significant interactions between mouse IgG2 class antibodies; these interactions are very common and may be prevented by either complete serum removal or use of alternate IgG1 clones. Such interactions represent a significant potential source of artifact in the use of whole blood lysis methods for specimen preparation for multicolor flow cytometry.