Line Immunoblot Assay for Tick-Borne Relapsing Fever and Findings in Patient Sera from Australia, Ukraine and the USA

Recombinant protein immunoblots for differential diagnosis of tick-borne relapsing fever and Lyme disease

Lyme disease (LD) is caused by a group of tick-borne bacteria of the genus Borrelia termed Lyme disease Borreliae (LDB). The detection of serum antibodies to specific LDB antigens is widely used to support diagnosis of LD. Recent findings highlight a need for serological tests that can differentiate LD from tick-borne relapsing fever (TBRF) caused by a separate group of Borrelia species termed relapsing fever Borreliae. This is because LD and TBRF share some clinical symptoms and can occur in overlapping locations. The development of serological tests for TBRF is at an early stage compared with LD. This article reviews the application of line immunoblots (IBs), where recombinant proteins applied as lines on nitrocellulose membrane strips are used to detect antibodies in patient sera, for the diagnosis and differentiation of LD and TBRF.

A serological assay to detect and differentiate rodent exposure to soft tick and hard tick relapsing fever infections in the United States

Human cases of relapsing fever (RF) in North America are caused primarily by Borrelia hermsii and Borrelia turicatae, which are spread by argasid (soft) ticks, and by Borrelia miyamotoi, which is transmitted by ixodid (hard) ticks. In some regions of the United States, the ranges of the hard and soft tick RF species are known to overlap; in many areas, recorded ranges of RF spirochetes overlap with Lyme disease (LD) group Borrelia spirochetes. Identification of RF clusters or cases detected in unusual geographic localities might prompt public health agencies to investigate environmental exposures, enabling prevention of additional cases through locally targeted mitigation. However, exposure risks and mitigation strategies differ among hard and soft tick RF, prompting a need for additional diagnostic strategies that differentiate hard tick from soft tick RF. We evaluated the ability of new and previously described recombinant antigens in serological assays to differentiate among prior exposures in mice to LD, soft or hard tick RF spirochetes. We extracted whole-cell protein lysates from RF Borrelia cultures and synthesized six recombinant RF antigens (Borrelia immunogenic protein A (BipA) derived from four species of RF Borrelia, glycerophosphodiester phosphodiesterase (GlpQ), and Borrelia miyamotoi membrane antigen A (BmaA)) to detect reactivity in laboratory derived (Peromyscus sp. and Mus sp.) mouse serum infected with RF and LD Borrelia species. Among 44 Borrelia exposed mouse samples tested, all five mice exposed to LD spirochetes were correctly differentiated from the 39 mice exposed to RF Borrelia using the recombinant targets. Of the 39 mice exposed to RF spirochetes, 28 were accurately categorized to species of exposure (71%). Segregation among soft tick RF species (Borrelia hermsii, Borrelia parkeri and Borrelia turicatae) was inadequate (58%) owing to observed cross-reactivity among recombinant BipA protein targets. However, among the 28 samples accurately separated to species, all were accurately assigned to soft tick or hard tick RF type. Although not adequately specific to accurately categorize exposure to soft tick RF species, the recombinant BipA protein targets from soft and hard tick RF species show utility in accurately discriminating mouse exposures to LD or RF Borrelia, and accurately segregate hard tick from soft tick RF Borrelia exposure.

IgG and IgM antibody formation to spike and nucleocapsid proteins in COVID-19 characterized by multiplex immunoblot assays

BACKGROUND

Rapid and simple serological assays for characterizing antibody responses are important in the current COVID-19 pandemic caused by SARS-CoV-2. Multiplex immunoblot (IB) assays termed COVID-19 IB assays were developed for detecting IgG and IgM antibodies to SARS-CoV-2 virus proteins in COVID-19 patients.

METHODS

Recombinant nucleocapsid protein and the S1, S2 and receptor binding domain (RBD) of the spike protein of SARS-CoV-2 were used as target antigens in the COVID-19 IBs. Specificity of the IB assay was established with 231 sera from persons with allergy, unrelated viral infections, autoimmune conditions and suspected tick-borne diseases, and 32 goat antisera to human influenza proteins. IgG and IgM COVID-19 IBs assays were performed on 84 sera obtained at different times after a positive RT-qPCR test from 37 COVID-19 patients with mild symptoms.

RESULTS

Criteria for determining overall IgG and IgM antibody positivity using the four SARS-CoV-2 proteins were developed by optimizing specificity and sensitivity in the COVID-19 IgG and IgM IB assays. The estimated sensitivities and specificities of the COVID-19 IgG and IgM IBs for IgG and IgM antibodies individually or for either IgG or IgM antibodies meet the US recommendations for laboratory serological diagnostic tests. The proportion of IgM-positive sera from the COVID-19 patients following an RT-qPCR positive test was maximal at 83% before 10 days and decreased to 0% after 100 days, while the proportions of IgG-positive sera tended to plateau between days 11 and 65 at 78-100% and fall to 44% after 100 days. Detection of either IgG or IgM antibodies was better than IgG or IgM alone for assessing seroconversion in COVID-19. Both IgG and IgM antibodies detected RBD less frequently than S1, S2 and N proteins.

CONCLUSIONS

The multiplex COVID-19 IB assays offer many advantages for simultaneously evaluating antibody responses to different SARS-CoV-2 proteins in COVID-19 patients.

Lyme Disease: Diversity of Borrelia Species in California and Mexico Detected Using a Novel Immunoblot Assay

Background: With more than 300,000 new cases reported each year in the United States of America (USA), Lyme disease is a major public health concern. Borrelia burgdorferi sensu stricto (Bbss) is considered the primary agent of Lyme disease in North America. However, multiple genetically diverse Borrelia species encompassing the Borrelia burgdorferi sensu lato (Bbsl) complex and the Relapsing Fever Borrelia (RFB) group are capable of causing tickborne disease. We report preliminary results of a serological survey of previously undetected species of Bbsl and RFB in California and Mexico using a novel immunoblot technique. Methods: Serum samples were tested for seroreactivity to specific species of Bbsl and RFB using an immunoblot method based on recombinant Borrelia membrane proteins, as previously described. A sample was recorded as seropositive if it showed immunoglobulin M (IgM) and/or IgG reactivity with at least two proteins from a specific Borrelia species. Results: The patient cohort consisted of 90 patients residing in California or Mexico who met the clinical case definition of chronic Lyme disease. Immunoblot testing revealed that 42 patients were seropositive for Bbsl (Group 1), while 56 patients were seropositive for RFB (Group 2). Eight patients were seropositive for both Bbsl and RFB species. Group 1 included patients who were seropositive for Bbss (14), B. californiensis (eight), B. spielmanii (10), B. afzelii/B. garinii (10), and mixed infections that included B. mayonii (three). Group 2 included patients who were seropositive for B. hermsii (nine), B. miyamotoi (seven), B. turicatae (nine), and B. turcica (two). In the remaining Group 1 and Group 2 patients, the exact Borrelia species could not be identified using the immunoblot technique. Conclusions: Lyme disease is associated with a diverse group of Borrelia species in California and Mexico. Current testing for Lyme disease focuses on detection of Bbss, possibly resulting in missed diagnoses and failure to administer appropriate antibiotic therapy in a timely manner. The genetic diversity of Borrelia spirochetes must be considered in future Lyme disease test development.