**4. Advancement of technology facilitates the progress in bovine immunology**

Technology is a critical factor that drives the advancement of science, and bovine immunology is not an exception, particularly regarding bovine CD4+ T cell research. In the late 80s, the study of bovine Th1/Th2 responses depended heavily on the measurement of cytokines in the supernatant of cultured CD4+ T cells through simple biological assays such as ELISA, or detection of IgG subtypes in the serum of infected animals through ELISA or immunoblotting techniques. In this context, upregulation of supernatant IFNγ and serum IgG2 would represent a Th1 response, upregulation of IL-4 and detection of serum IgG1 would indicate a Th2 response [18, 80], and detection of both cytokines and both IgG subtypes (IgG1 and

### *CD4+ T Cell Responses to Pathogens in Cattle DOI: http://dx.doi.org/10.5772/intechopen.100410*

IgG2) would represent a Th0 response [142]. In the late 90s, advancements in molecular biology enabled scientists to measure cytokines at the transcriptional level (mRNA). Thus, reverse transcription polymerase chain reaction (RT-PCR) was commonly used to detect the presence of mRNA of Th1/Th2 cytokines in PBMCs, DLNs, and tissues of infected cattle [143–145]. In the next decade, the advent of quantitative PCR (qPCR) improved the detection of Th1/Th2 transcripts from a qualitative to a quantitative level [146]. Later, with the invention and use of flow cytometry, scientists were able to measure protein production of Th1/Th2 cytokines on a population level [147]. More recently, some very exciting technological advancements have been developed, such as single-cell RNA sequencing, proteomics, metabolomics, confocal microscopy, which are considered excellent tools for a deeper understanding of immune mechanisms [148–152]. Therefore, the advancement of bovine immunology research is closely associated with the development of novel technology in science, especially in the context of understanding Th1/Th2 responses in cattle.
