CD4 and peripheral nerve injury: The noteworthy results here provide the first evidence that inflammatory CD4+ αβ T cells (IFNγ-expressing Th1 cells) selectively enter into the DR leptomeninges along the somatosensory pathways for the transmission of mechanical allodynia; these antigen-specific and MHC II-restricted T cells contribute to the development of chronic mechanical allodynia after peripheral nerve injuries (Fig. 8).