“…It has been further shown that the capacity to manifest delayed hypersensitivity reactions and in vitro lymphoblast transformation of blood lymphocytes by phytohemagglutinin, are due to thymus dependent small lymphocytes [20]. In addition, impaired lymphocyte transformation has been ob served in diseases involving immunological disorders, as in ataxiatelangiectasia [46,68,77], agammaglobulinemia [9], Sjogren's syndrome [47], congenital absence of the thymus [22,44,50] and thymic dysplasia [29,56]. The available evidence strongly indicates that the in vitro lymphocyte transformation is related to the cellular immune reactions, particularly to the delayed hypersensitivity [8,21,29,43,60,69], although a recent report offers evidence indicating that it is related to both cellular and humoral immune reactions [12].…”