Novartis Vaccines Institute for Global Health, Via Fiorentina 1, 53100 Siena, Italy.
J Immunol Methods. 2013 Jan 31;387(1-2):121-9. doi: 10.1016/j.jim.2012.10.005. Epub 2012 Oct 22.
Nontyphoidal isolates of Salmonella (NTS), particularly Salmonella Typhimurium, are a major cause of invasive bacteremia in Africa. Despite this, no vaccine against NTS is currently available for use in humans. If a NTS vaccine is to be developed in a timely manner, there is a need to develop assays to assess its in vivo efficacy. Assessment of potential efficacy of candidate vaccines in preclinical models is important for proof-of-concept and reduces attrition of vaccines in clinical trials. Serum bactericidal assays (SBA) are often used to assess the functional activity of vaccine-induced antibody responses targeted against Gram-negative bacteria with results given as the maximum dilution of serum that can effect bacterial killing. Previously we have found evidence for a protective role for antibody-induced complement-mediated killing of NTS in African children using an undiluted whole serum SBA. However, endogenous complement in diluted human sera is limiting and insufficient to effect bactericidal activity against S. Typhimurium beyond two two-fold dilutions. In the current study, we examined the requirements for SBA against NTS using baby rabbit serum (BRS) as an exogenous source of complement. We found that the amount of complement required for antibody-mediated bactericidal activity is much higher for the invasive African S. Typhimurium isolate D23580, compared with the laboratory S. Typhimurium LT2 and Salmonella Paratyphi A CVD1901. While 20% BRS was sufficient to kill LT2 and CVD1901, 75% BRS was needed to kill D23580. Our findings demonstrate that one concentration of exogenous complement is not suitable for SBA against all Salmonella isolates. To develop SBA to assess the in vivo efficacy of Salmonella vaccines, it is necessary to optimize the assay for the Salmonella isolates against which the vaccine is targeted.
非伤寒型沙门氏菌（NTS），尤其是鼠伤寒沙门氏菌，是非洲侵袭性菌血症的主要原因。尽管如此，目前还没有针对 NTS 的人类可用疫苗。如果要及时开发 NTS 疫苗，就需要开发评估其体内疗效的检测方法。在临床前模型中评估候选疫苗的潜在疗效对于概念验证很重要，并可减少疫苗在临床试验中的淘汰率。血清杀菌试验（SBA）常用于评估针对革兰氏阴性菌的疫苗诱导抗体反应的功能活性，结果以能有效杀死细菌的血清最大稀释度表示。以前，我们使用未经稀释的全血清 SBA 发现了针对 NTS 的抗体诱导补体介导杀伤在非洲儿童中具有保护作用的证据。然而，稀释人血清中的内源性补体是有限的，不足以对鼠伤寒沙门氏菌以外的细菌产生杀菌活性超过两个两倍稀释度。在本研究中，我们使用兔幼仔血清（BRS）作为外源性补体来源，研究了针对 NTS 的 SBA 的要求。我们发现，与实验室鼠伤寒沙门氏菌 LT2 和副伤寒 A 沙门氏菌 CVD1901 相比，用于抗体介导杀菌活性的补体需求量更高。虽然 20%的 BRS 足以杀死 LT2 和 CVD1901，但需要 75%的 BRS 才能杀死 D23580。我们的研究结果表明，一种浓度的外源性补体并不适合针对所有沙门氏菌分离株的 SBA。为了开发 SBA 来评估沙门氏菌疫苗的体内疗效，有必要针对目标沙门氏菌分离株优化该检测方法。
