Figure 7

Pre-TCR and pre-BCR. Schematic drawing of pre-T cell receptor (pre-TCR; thymus, large pre-T cell with rearranged TCRβ gene) and pre-B cell receptor (pre-BCR; bone marrow, large pre-B cell with rearranged IgHμ gene). Defects of the pre-TCR, subdivided into defects of V(D)J recombination and defects of signaling through the pre-T cell receptor, cause arrest of the development of T lymphocytes at the stage of large pre-T cell and therefore SCID; defects of the pre-BCR cause arrest of the development of B lymphocytes at the stage of large pre-B cell and therefore agammaglobulinemia.