EUVAC.NET collaborative study: evaluation and standardisation of serology for diagnosis of pertussis.

As part of the new EUVAC.NET contract with ECDC (Pertussis Work Area 4), a collaborative study was organised in July-December 2010. Two well-defined reference preparations with high and low IgG antibodies to pertussis toxin (PT), were sent to participants. The purposes of this study were to assess current laboratory performance of serological assays for pertussis; to compare in-house reference preparations that are currently used by participants for the serological assay; and to identify needs for standardisation of the serological assay. Reference Laboratories in Europe currently performing serological assays for the diagnosis of pertussis by measuring antibody to PT, were invited to participate in the study. A total of 17 laboratories/countries participated in this study. Results were reported from a total of 9 participants who used in-house ELISA assays and 10 participants who used commercial kits. All participants using in-house ELISA with purified PT coating plates distinguished the 2 preparations and gave results that were comparable to the expected values. A total of 6 commercial kits included in the study showed different results. The kits coated with mixture antigens did not appear to be able to give results that were correlated to the WHO reference preparations.

Characterization of reference materials for human antiserum to pertussis antigens by an international collaborative study.

Enzyme-linked immunosorbent assay (ELISA) has been widely used to evaluate antibody responses to pertussis vaccination and infection. A common reference serum is essential for the standardization of these assays. However, no internationally recognized reference serum is available. At the request of the Expert Committee on Biological Standardization (ECBS) of the World Health Organization (WHO), a set of four candidate international standards has been prepared. These candidate materials have been assessed for suitability and compared to the widely used U.S. reference pertussis antiserum (human) lot 3, lot 4, and lot 5 by 22 laboratories from 15 countries in an international collaborative study. Laboratories measured immunoglobulin G (IgG) and IgA antibodies to pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (PRN), and fimbriae (Fim2&3) using their established immunoassays. The results of this study showed each of the four candidates to be suitable as an international standard. With the agreement of the participants, a recommendation has been made to the ECBS that the candidate material coded 06/140 be established as the First International Standard for pertussis antiserum (human), with the following assigned international units (IU): IgG anti-PT, 335 IU/ampoule; IgA anti-PT, 65 IU/ampoule; IgG anti-FHA, 130 IU/ampoule; IgA anti-FHA, 65 IU/ampoule; IgG anti-PRN, 65 IU/ampoule; and IgA anti-PRN, 42 IU/ampoule. No formal units have been proposed for anti-Fim2&3 because most assays used a mixture of fimbrial antigens. In addition, the candidate material coded 06/142 has been proposed as a WHO working preparation for characterization of assay systems.

Use of monoclonal antibodies to serotype Bordetella pertussis isolates: comparison of results obtained by indirect whole-cell enzyme-linked immunosorbent assay and bacterial microagglutination methods.

Sixty-one Bordetella pertussis isolates were tested blindly in two laboratories to determine their serotype nature by monoclonal antibodies using two independent methods: the standard bacterial microagglutination assay and an indirect whole-cell enzyme-linked immunosorbent assay. Both methods gave concordant results in 60 of the 61 isolates.

Determination of serum antibody to Bordetella pertussis adenylate cyclase toxin in vaccinated and unvaccinated children and in children and adults with pertussis.

Presence of antibody to adenylate cyclase toxin (ACT) has been noted following Bordetella pertussis infection. Because ACT is not presently in any acellular pertussis vaccines, it has been considered as a possible antigen to use in B. pertussis diagnostic enzyme-linked immunosorbent assay (ELISA) studies. We determined antibody to B. pertussis ACT by ELISA and Western blot tests in serum samples obtained from unvaccinated children, from children vaccinated with several diphtheria and tetanus toxoid vaccines (DTP vaccines), from children vaccinated with vaccines containing acellular pertussis components in combination with diphtheria and tetanus toxoids (DTaP vaccines), and from children and adults with pertussis. Primary infections with either B. pertussis or Bordetella parapertussis stimulated a vigorous antibody response to ACT. In contrast, patients in whom DTP and DTaP vaccines failed had minimal ACT antibody responses. The lack of a significant ACT antibody response in children in whom the vaccine failed is of interest but would seem to preclude the use of ACT in diagnostic tests.