Melittin, a bee venom peptide, can activate the immune system against porcine reproductive and respiratory syndrome viruses (PRRSV) by upregulating Th1 cytokines (IL-12 and IFN-) and other immune cells, such as gd-T cells, CD3+–CD8+, and CD4+–CD8+, causing a decrease in viral load and a reduction in infection severity (in pigs infected with PRRSV) [137]. The gene discussed is CD8A; the disease is infection.