TBX21 and infection: However, comparison of resistant and susceptible animals showed that there was no differential expression of any of the three master regulators (or variants) that control T cell polarization, TBX21, GATA3 or RORC2. A possible explanation for this is that the lymph nodes studied had been responding to T. circumcincta infection for 12 weeks and that the regulatory events controlling T cell polarization occurred much earlier in infection; during initial activation of T helper cells.