Although recognized as fundamental aspects of T lymphocyte development , only recently have the mechanisms governing positive and negative selection been examined at a molecular level .
although recognized as fundamental aspects of t lymphocyte development , only recently have the mechanisms governing positive and negative selection been examined at a molecular level .
O O O O O O B-cell_type I-cell_type O O O O O O O O B-other_name O B-other_name I-other_name O O O O O O O