In recent years, numerous qualitative discoveries have been made in immunology research. However, the effect of quantitative events, long recognized as the driving factors for determinism in developmental biology, that dictate the quality of the immune response elicited to an antigen in concert with microbial products still requires serious attention. Here we discuss how the often-neglected issue of quantification affects the specification, differentiation and commitment of helper T cells. As reductionist in vitro approaches have been instrumental in the elucidation of the factors determining the development of helper T cells, in this perspective we highlight the need for the standardization of protocols, also fundamental for the comparison of immune responses in mice and humans. Improving understanding of how these in vitro quantitative events translate to immune responses in vivo, which can be studied in mouse models, is of importance in obtaining information on immune responses in humans, thus empowering translational research.