ABSTRACT
Some double-negative cells (representing about 20% of all double-negative cells in the thymus) express the genes encoding the rare g:d receptor; these cells represent a separate developmental lineage of CD4-CD8-thymocytes. A second double-negative population expresses the pre-T receptor; these cells mature into double-positive (CD4+CD8+) thymocytes. Once the mature T-cell receptor a chain is expressed, these rapidly proliferating cells phosphorylate RAG-2 protein and degrade it; consequently there is no further gene arrangement.
