Late onset allergic reactions can also be referred to as T cell-mediated type IV hypersensitivity reactions, as the name implies allergic reactions are relatively slow, occurring 24-72 hours after invasion, and are primarily inflammatory reactions with single nucleated cells infiltrating tissue damage, occurring independent of antibodies and complement. The common ones are mainly infectious delayed allergic reactions, such as tuberculous injury, and contact delayed allergic reactions, such as contact dermatitis. Less commonly, such hypersensitivity reactions occur in transplant rejection allogeneic, intergenic transplants, often mediated by T cells.