Submitted August 13, 2008
Accepted January 9, 2009
Murine neonatal recent thymic emigrants (RTE) are phenotypically and functionally distinct from adult RTE
Shannon J Opiela, Tulay Koru-Sengul, and Becky Adkins*
Department of Microbiology and Immunology, University of Miami Miller School of Medicine, Miami, FL, United States
Department of Epidemiology and Public Health, University of Miami Miller School of Medicine, Miami, FL, United States
* Corresponding author; email: radkins{at}med.miami.edu.
In contrast to adults, the murine neonatal CD4+ compartment contains a high frequency of recent thymic emigrants (RTE). However, the functional capabilities of these cells in neonates are relatively unknown. Moreover, it has not been determined whether RTE from neonates and adults are comparable. Here we have directly compared neonatal and adult CD4+ RTE for the first time, using a transgenic mouse strain that allows for the identification and purification of RTE. Our data demonstrate that RTE from murine neonates and adults are phenotypically and functionally distinct. In particular, although the magnitude of RTE cytokine responses from both age groups is dependent on the conditions of activation, neonatal RTE always exhibited higher levels of effector Th1/Th2 cytokine production than adult RTE. In addition, neonatal, but not adult, RTE showed early proliferation in response to stimulation with IL-7 alone. This was associated with faster kinetics of IL-7R
downregulation and higher levels of pSTAT5 in neonatal RTE. These quantitative and qualitative differences in the neonatal and adult RTE populations may at least partially explain the diverse responses that are elicited in vivo in neonates in response to different conditions of antigen exposure.
