Answer:
The given blank can be filled with thymus.
Step-by-step explanation:
The secondary branch of immunological tolerance known as the peripheral tolerance occurs in the immune periphery, that is, post the maturation and exit of the B and the T cells from the primary lymphoid organs like thymus. The main objective of the mechanism is to make sure that the self-destructive B and T cells that managed to pass through central tolerance do not result in autoimmune disease.