Expression of the interleukin-2 receptor γ chain on cord blood mononuclear cells

Lymphocytes in umbilical cord blood and neonatal peripheral blood have been shown to have less ability in an immune reaction. In our present experimental approach to address this issue, we made use of the cord blood of full-term birth infants to investigate the expression of the interleukin-2 receptor γ (IL-2Rγ) chain that is shared with receptors for IL-4, IL-7, IL- 9, and IL-15 as well as IL-2. The γ chain expression in cord blood lymphocytes was about one-third that in the lymphocytes of adults, whereas no significant difference between cord blood and adult monocytes was observed. A reduced expression of the γ chain was observed in all of the CD4⁺ T cells, CD8⁺ T cells, γδ T cells, B cells, CD16⁺ natural killer (NK) cells, and CD56(bright) NK cells of the cord blood lymphocytes. The reduced γ chain expression reached two-thirds of that in adults after 3 days of culture in vitro and in infants 3 days after birth, thus implying that the increase in the γ chain may significantly contribute to the prevention of neonatal infection.