Furthermore, the expression level of TLR4, HSP70, caspase3, NF-κB, and the pro-apoptotic Bax was significantly upregulated while the anti-apoptotic Bcl2 was downregulated in Cd-treated birds which suggested that HSP70/TLR4/NF-κB signaling pathway may be involved in the molecular mechanism of Cd immunotoxicity which is confirmed by the excessive damage of the BF tissue with marked lymphopenia, vacuolation, and follicular atrophy. The gene discussed is BAX; the disease is lymphopenia.