Evaluation of anticoagulants for serologic assays of cholera vaccination

Effects of anticoagulants and Ficoll on human serum antibody reactivities and functions against Mycobacterium tuberculosis

The ability to utilize leftover samples containing anticoagulants or Ficoll would provide substantial opportunities for future antibody and biomarker studies. Some anticoagulants might influence antibody reactivity against pathogens, but comprehensive studies investigating effects in the context of TB are lacking. We enrolled 24 individuals with and without history of M. tuberculosis and/or HIV-infection and investigated TB antibody reactivities, function, and other host protein biomarkers in simultaneously obtained serum and plasma from serum separation, EDTA, heparin, acid citrate dextrose (ACD), or mononuclear cell preparation (CPT™) tubes which contain heparin and Ficoll. Antibody isotype reactivities to two mycobacterial antigens, as well as phagocytosis of M. tuberculosis, correlated strongly and significantly between serum and plasma, irrespective of type of anticoagulant or Ficoll present (r ≥ 0.85, p < 0.0001). However, the presence of ACD resulted in slightly lower values than those obtained with serum in both indirect (antibody reactivities to mycobacterial antigens) and Sandwich ELISAs (soluble CD14 measurements). Our data demonstrate that leftover plasma, regardless of containing anticoagulants or Ficoll, can be used in TB antibody or other host protein biomarker studies but suggest the value of a correction factor when using ACD plasma interchangeably with serum in antibody binding studies.

Immunogenicity of a bivalent killed thimerosal-free oral cholera vaccine, Euvichol, in an animal model

PURPOSE

An oral cholera vaccine (OCV), Euvichol, with thimerosal (TM) as preservative, was prequalified by the World Health Organization (WHO) in 2015. In recent years, public health services and regulatory bodies recommended to eliminate TM in vaccines due to theoretical safety concerns. In this study, we examined whether TM-free Euvichol induces comparable immunogenicity to its TM-containing formulation in animal model.

MATERIALS AND METHODS

To evaluate and compare the immunogenicity of the two variations of OCV, mice were immunized with TM-free or TM-containing Euvichol twice at 2-week interval by intranasal or oral route. One week after the last immunization, mice were challenged with Vibrio cholerae O1 and daily monitored to examine the protective immunity against cholera infection. In addition, serum samples were obtained from mice to measure vibriocidal activity and vaccine-specific IgG, IgM, and IgA antibodies using vibriocidal assay and enzyme-linked immunosorbent assay, respectively.

RESULTS

No significant difference in immunogenicity, including vibriocidal activity and vaccine-specific IgG, IgM, and IgA in serum, was observed between mice groups administered with TM-free and -containing Euvichol, regardless of immunization route. However, intranasally immunized mice elicited higher levels of serum antibodies than those immunized via oral route. Moreover, intranasal immunization completely protected mice against V. cholerae challenge but not oral immunization. There was no significant difference in protection between two Euvichol variations.

CONCLUSION

These results suggested that TM-free Euvichol could provide comparable immunogenicity to the WHO prequalified Euvichol containing TM as it was later confirmed in a clinical study. The pulmonary mouse cholera model can be considered useful to examine in vivo the potency of OCVs.

Prospective evaluation of accuracy and clinical utility of the Dual Path Platform (DPP) assay for the point-of-care diagnosis of leptospirosis in hospitalized patients

Early detection of leptospirosis with field-ready diagnostics may improve clinical management and mitigate outbreaks. We previously validated the point-of-care Dual Path Platform (DPP) for leptospirosis with sera in the laboratory. This prospective study compares the diagnostic accuracy and clinical utility of the DPP using finger stick blood (FSB) against the serum DPP, venous whole blood (VWB) DPP, IgM-ELISA, and clinical impression. We sequentially enrolled 98 patients hospitalized for acute febrile illnesses, of which we confirmed 32 by leptospirosis reference tests. Among syndromes consistent with classic leptospirosis, the FSB DPP showed similar sensitivity and specificity (Se 93% and Sp 80%), and positive and negative predictive values (PPV 74% and NPV 95%), to VWB DPP (Se 96%, Sp 75%, PPV 68%, and NPV 97%), serum DPP (Se 85%, Sp 87%, PPV 79%, and NPV 91%) and IgM-ELISA (Se 81%, Sp 100%, PPV 100%, and NPV 90%). The FSB DPP provided a favorable likelihood ratio profile (positive LR 4.73, negative LR 0.09) in comparison to other assays and clinical impression alone. Additionally, we identified four of five leptospirosis-associated meningitis patients by whole blood DPP, none of which clinicians suspected. This demonstrates potential for the DPP in routine detection of this less common syndrome. The FSB DPP demonstrated similar discrimination for severe human leptospirosis compared with serum assays, and it is a simpler option for diagnosing leptospirosis. Its performance in other epidemiological settings and geographic regions, and for detecting atypical presentations, demands further evaluation.

The reliable, portable, point-of-care DPP assay effectively discriminates case status for patients presenting to hospital with acute febrile syndromes consistent with classic leptospirosis. Diagnostic accuracy of the finger stick DPP using the initial acute-phase specimen at the bedside is similar to serum DPP and IgM-ELISA, yet diagnosticians can perform the DDP assay in 20 minutes without laboratory equipment. The finger stick DPP expands rapid diagnostic options at the bedside for severe leptospirosis in humans.

Preanalytical Stability of Antibodies to Pathogenic Antigens

Background: Serologic testing for antibodies against epitopes from pathogens is a valuable tool for investigating the relationship between infection and disease. This study comprehensively evaluates the impact of preanalytic variation on antibody seropositivities to a selected set of antigens arising from delays in processing of blood samples, preprocessing storage temperature, and vacutainer type.Methods: We assessed peripheral blood collected from 29 volunteers in four different Vacutainer types [ethylenediaminoetetraacetic acid (EDTA), acid-citrate-dextrose (ACD), lithium heparin (LH), serum separator tubes (SST)], and stored at 4°C or room temperature for 0, 1, 2, 3, 4, 5, and 6 days before processing. Multiplex serology was used to determine antibody reactivity against 35 antigens derived from human papillomaviruses, human polyomaviruses, Epstein-Barr virus, and Helicobacter pylori Cohen's κ statistic was used to measure agreement on seropositivity status between samples exposed to standard and nonstandard clinical practice conditions.Results: For samples processed without delay, κ was not associated with storage-temperature (P value range 0.23 to 0.95) or vacutainer type (P value range, 0.35-0.89). Kappa did not significantly decline with increasing delays in processing for any vacutainer-type storage temperature combination (P slope range, 0.06-1.00).Conclusions: Antibodies to epitopes from various pathogenic infectious agents can be measured reliably from samples stored in SST, EDTA, ACD, or LH vacutainers at either room temperature or 4°C for up to 6 days before processing.Impact: Serologic testing is robust to several preanalytic options. These findings are particularly important for epidemiologic studies recruiting participants from remote settings where sample exposure to preanalytic conditions can vary considerably. Cancer Epidemiol Biomarkers Prev; 26(8); 1337-44. ©2017 AACR.

Serum bactericidal assay for the evaluation of typhoid vaccine using a semi-automated colony-counting method

Typhoid fever, mainly caused by Salmonella enterica serovar Typhi (S. Typhi), is a life-threatening disease, mostly in developing countries. Enzyme-linked immunosorbent assay (ELISA) is widely used to quantify antibodies against S. Typhi in serum but does not provide information about functional antibody titers. Although the serum bactericidal assay (SBA) using an agar plate is often used to measure functional antibody titers against various bacterial pathogens in clinical specimens, it has rarely been used for typhoid vaccines because it is time-consuming and labor-intensive. In the present study, we established an improved SBA against S. Typhi using a semi-automated colony-counting system with a square agar plate harboring 24 samples. The semi-automated SBA efficiently measured bactericidal titers of sera from individuals immunized with S. Typhi Vi polysaccharide vaccines. The assay specifically responded to S. Typhi Ty2 but not to other irrelevant enteric bacteria including Vibrio cholerae and Shigella flexneri. Baby rabbit complement was more appropriate source for the SBA against S. Typhi than complements from adult rabbit, guinea pig, and human. We also examined the correlation between SBA and ELISA for measuring antibody responses against S. Typhi using pre- and post-vaccination sera from 18 human volunteers. The SBA titer showed a good correlation with anti-Vi IgG quantity in the serum as determined by Spearman correlation coefficient of 0.737 (P < 0.001). Taken together, the semi-automated SBA might be efficient, accurate, sensitive, and specific enough to measure functional antibody titers against S. Typhi in sera from human subjects immunized with typhoid vaccines.

•

Improved SBA against S. Typhi was developed using a colony counting system.

•

The improved SBA was specific to S. Typhi but not to other gram-negative bacteria.

•

There was a good correlation between SBA and anti-Vi IgG titers in vaccinee’s sera.

•

This SBA would be useful for the clinical immuno-monitoring of typhoid vaccines.