Thymic development of V gamma 3 cells

Several characteristics of V gamma 3 cells are clearly different from those of other T cells. V gamma 3 thymocytes mainly originate from fetal precursor cells and only differentiate efficiently in a fetal thymic environment. Evidence is discussed that the early appearance of V gamma 3 cells is probably due to differential gene accessibility which regulates gene rearrangement. Another characteristic of V gamma 3 cells is the canonical sequence of their T-cell receptor (TCR), which seems to be mainly shaped intracellularly by the combination of targeted gene rearrangement, homology-directed recombination and the absence of terminal deoxynucleotidyl transferase, rather than by cellular selection. Contrary to alpha beta cells, V gamma 3 cells express the Fc epsilon RI gamma chain in their TCR complex and other protein tyrosine kinases are important for their thymic differentiation. Also, expression of several cell surface markers is regulated differently on V gamma 3 cells as compared to alpha beta cells. Collectively, these findings show that V gamma 3 cells are a separate lineage of T cells with unique requirements for proper thymic differentiation and survival.