memory T-cells) when compared to other assays[8],[9]. of interferon- spot forming cells in human peripheral blood mononuclear cells stimulated withMycobacterium tuberculosisderived antigens. The differences in the protocols were compared directly. We found that several sources of variation in assay protocols can be eliminated, for example by avoiding serum supplementation and using AIM-V serum free medium. In addition, the number of cells added to ELISpot wells should also be standardised. Importantly, delays in peripheral blood mononuclear cell processing before stimulation had a marked effect on the number of detectable spot forming cells; processing delay thus should be minimised as well as standardised. Finally, a pre-stimulation culture period improved the sensitivity of the assay, however this effect may be both antigen and donor dependent. In conclusion, small differences in ELISpot protocols in routine use can affect the results obtained and care should be given to conditions selected for 6-Maleimido-1-hexanol use in a given study. A pre-stimulation step may improve the sensitivity of the assay, particularly when cells have been previously frozen. == Introduction == In the absence of any reliable surrogate markers of protection against tuberculosis (TB) the monitoring of vaccine-induced immunity using an effective assay for immune markers is considered the best selection criterion for moving a new vaccine candidate forward from Phase 1 and IIa safety and immunogenicity studies through into Phase IIb and Phase 3 efficacy testing. Markers associated with protection against disease have not yet 6-Maleimido-1-hexanol been identified, although multiple efforts are ongoing in biomarker identification and validation[1][3]. The production of interferon- (IFN-), a Th1 cytokine, is frequently measured as an indicator of immune activity against TB. Although its presence does not directly imply protection against development of disease, studies have revealed it to be at least an important component of a protective immune phenotype[4][7]. The ELISpot assay is an effective tool to enumerate the number of cells producing IFN- in response to a whole series of antigens, including peptides, peptide pools, proteins and crude bacterial extracts. Tailor-made selection of antigens can be made, which for vaccine trials will include specific vaccine components as well as positive and negative controls. In addition, the ELISpot assay has proven particularly sensitive in the detection of low-level responses (i.e. memory T-cells) when compared to other assays[8],[9]. The great advantages of ELISpot are the lack of assay-specific equipment essential for assay performance, especially when considering developing countries as important and necessary trial sites for Phase II and III evaluation, its relative high-throughput performance and its potential robustness. Although ELISpot assays will yield potentially very important data, results may be influenced by variations in the protocol or even by execution of the same protocol by different laboratory members[10]. Especially for monitoring of immune responses where longitudinal follow up of individual patients or volunteers is usually desirable, it is extremely important to have comparable results in all assays. Monitoring immunity by ELISpot becomes even more complicated when executed at different study sites between which data will have to be compared. Depending on the exact study set up and research questions, samples can be assayed in real-time, implicating assay variation between follow up time points of each single volunteer, or all longitudinal samples from a volunteer can be analysed in a single assay to minimize inter-assay variation and theoretically increase assay sensitivity. Both strategies have their own advantages and disadvantages, the most significant being freezing and thawing of PBMCs in the case 6-Maleimido-1-hexanol of batch analysis. New and frozen cells may need different protocols to yield optimal ELISpot results. The addition of a pre-incubation step to improve assay level of sensitivity for freezing materials might solve the issue of reduced indicators, but side-by-side evaluations are lacking. With this paper we analysed multiple elements that are of potential significance for ELISpot efficiency and identified the ones that should become harmonized between laboratories if evaluations between immune system responses should be made. Like a starting place we likened 6-Maleimido-1-hexanol ELISpot protocols found in the writers’ laboratories and determined the major 6-Maleimido-1-hexanol variations in strategy (Desk 1). Where suitable, these variations may be eradicated for better unity between research, or indeed utilized to identify the very best strategy for confirmed study with regards to the particular circumstances. Also of take note are process steps which many protocols consent like the commercial way to obtain antibody pairs. Although the reason why for this aren’t necessarily medical but could be due to effective marketing and suggestion by person to person, a solid case may be designed for organizations who usually do not use these reagents to look at them. == Desk 1. Major variations (and commonalities) in ELISpot protocols posted by Dll4 4 participant laboratories. == == Components.