The likely activation of Th1/Th17 T cell populations in conjunction with the simultaneous increment of the inflammatory cytokines/chemokines (TNF, IL-1β, IL-6, MCP-1, and MIP-1β) in response to BCG could explain the onset of paucibacillary leprosy (PB) in a small percentage of leprosy contacts after vaccination[28][10][34][35]. The gene discussed is IL1B; the disease is leprosy.