The immune system responds differently to pathogens that infect intracellularly, such as viruses, than it does when responding to extracellular pathogens, like most bacteria. The MMR vaccine is a combination vaccine used against three viruses. Our bodies develop immunity through a series of steps that result in the activation of cytotoxic T cells against virally-infected cells. Place the following steps for T cell activation in the correct order. First Step to Last Step:1. A helper T cell binds to the MHC-II protein of an infected dendritic cell.2. The dendritic cell secretes IL-12 to differentiate the helper T cell into a type 1 helper T cell.3. Dendritic cells infected with the virus migrate to lymph nodes.4. Activated cytotoxic T cells undergo clonal expansion. The type 1 helper T cell secretes IL-2 to activate the cytotoxic T cell.5. Activated cytotoxic T cells self-stimulate and leave the lymph node.6. A cytotoxic T cell binds to the MHC-I protein of an infected dendritic cell.