ABSTRACT
The developmental pathways of T and B lymphocytes have much in common: both cell types derive from bone marrow stem cells and, during development, they must undergo gene rearrangement to produce their antigen receptors. However, whereas B cells rearrange their immunoglobulin genes while remaining in the bone marrow, the precursors of T cells have to leave the bone marrow and enter another primary lymphoid organ-the thymus-before they rearrange their T-cell receptor genes. Gene rearrangements in developing T cells proceed in a broadly similar fashion to those in B cells, but with key differences. The main one being the formation of two distinct T-cell lineages: one expressing α:β receptors and the other γ:δ receptors (see Section 5-5).
