Song et al. (2016) investigated methicillin-resistant Staphylococcus aureus infection of mammary epithelial cell lines and found substantial downregulation of TRAPPC9 expression 6 h after infection (p < 0.05). The cluster of differentiation 4 (CD4) gene is located on chromosome 5 in cattle (GENE ID: 407098). CD4 is an accessory protein that binds non-covalently to the T cell receptor and recognizes an invariant region of MHC class II proteins on antigen-presenting cells (Napolitano et al., 2021). The gene discussed is CD4; the disease is infection.