Every molecule in the body is made from instructions in a gene and everybody's genes are slightly different. For more about MHC molecules try this lecture. There are 3 main types of T cells. They're a bit like the NK cells but more specific. These are clever bacteria because they can avoid being killed by the lethal processes that occur in phagocytosis.
Macrophages can become so overcome with the bacteria that they start to die and a granuloma forms.
The T inflammatory cells look for macrophages that have phagocytosed some intracellular bacteria and need assistance to deal with them. Messages are also sent to call for more back-up from other macrophages. These messages are in the form of chemicals called cytokines. The Complement system is a group of proteins found in the blood and tissues. Each is known by a capital C followed by a number.