CD4 and asthma: CD4+ lymphocytes producing Th2 cytokines are common for extrinsic asthma phenotype, however, as mRNA of Th2 type IL-13 was mainly suppressed by the materials in our study and not significantly changing at protein level except in response to CuO NH3, involvement of other types of CD4+ Th lymphocytes in responses driven by CuO nanomaterials might be possible.