**2.1 Immunological tolerance**

To keep the body healthy, the immune system is expected to entail invading pathogens while avoiding reactivity to self-tissues. This so-called immunological tolerance engages both central and peripheral modes of action (for review, see [5]).

## *2.1.1 Central tolerance*

It is referred to immature B and T cells when they are present in the primary lymphoid organs—B cells in the bone marrow and T cells in the thymus. Mechanisms of central tolerance are, for example, clonal deletion and elimination of self-reactive cells.
