A systematic review and risk of bias analysis of in vitro studies on trophoblast response to immunological triggers

An increasing amount of evidence suggests that immune responses may affect trophoblast functioning, which in turn may play a role in gestational disorders and fetal development. This systematic review offers the first summary of in vitro studies on the trophoblast response to immunological triggers, in conjunction with a risk of bias analysis. A search in Pubmed and Embase yielded 110 relevant studies. Primary trophoblasts were the most commonly used cell type, but trophoblast subtypes were not always defined. Similarly, the exact natures of trophoblast cell lines were sometimes unclear. Cytokines and Toll-like receptor agonists were often used as interventions, but most studies focused on a select few substances such as tumor necrosis factor-α and lipopolysaccharide. In regard to the outcome parameters, some important trophoblast functions, such as hormone production and barrier formation were underrepresented. Whether or not risk of bias was high varied strongly between types of bias. Risk of selection bias, for example, was usually low. However, none of the included studies mentioned blinding or plate randomization. Only a select few studies mentioned passage numbers, use of vehicle control or conflict of interest. In conclusion, better characterization of trophoblast subtypes and a broader range of studied interventions and outcome parameters would contribute to a more complete understanding of trophoblast responses to immune stimuli. Additionally, researchers are encouraged to replicate experiments and pay close attention when setting up and writing down methodologies, in order to improve the reproducibility and translatability of their work.