CD4 and infection: In conclusion, young-adult cats infected with SARS-CoV-2 developed a strong antiviral immune response shortly after infection, as shown by a large number of antiviral DEGs on DPI 2 in the CD4+ subset in blood, increased percentages of CD4+ and CD8+ cells in the blood on DPI 7 and the presence of virus-neutralizing antibodies on DPI 7.