TLR4 and lymphopenia: 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.