CD4 and viral infectious disease: IRF7 is a key transcription factor in response to viral infections and CD4+ T cell in IRF7-deficient patients shows dysregulated IFNγ production.32 CD30L-deficient mice showed impaired Th1 responses against M. bovis bacillus Calmette-Guérin infection, suggesting that CD30L/CD30 signalling induced by CD30+-CD30L+ T cell interaction play an important role in amplification of Th1 responses.33 PD-L2 is known to inhibit aberrant T cell activation.