The difference in the pathogenicity displayed in different chicken breeds can be due to the existence of some avian genes such as PLAU, VCAM1, TNFRSF1A, and PGF gene, which were downregulated during inflammatory response in the lungs of the chicken breed, which can affect disease tolerance; the commercial broiler in Spain was reported to be resistant toward the clade 2.3.4.4b H5N8 HPAIV infection [45]. The gene discussed is PGF; the disease is infection.