Human immunodeficiency virus type 1 (HIV-1) is responsible for acquired immunodeficiency syndrome (AIDS). During the progression of this disease, the vital cells that are effective in the immune system -helper T cells (CD4+ T cells, T cells that contain CD4), macrophages, and dendritic cells (which present antigenic material to the cell surface of T cells)are infected by HIV. Consequently, the number of CD4+ T cells decreases, leading to cell death in the host. When the number of CD4+ T cells reaches a critical point, cell-mediated immunity is lost and the body becomes sensitive to infections, resulting in AIDS .