An evaluation of the neonatal immune system using a listeria infection model.
BACKGROUND
T helper 1 (Th1)/T helper 2 (Th2)-biased cytokine regulation may be another reason that neonates are much more susceptible to infectious disease than are adults.


OBJECTIVE
We attempted to determine the ability of neonatal mice to direct the Th1 phenotype against Listeria monocytogenes (LM), because LM, an intracellular Gram-positive bacterium, induces profound cellular immunity by Th1 cells in vivo.


METHODS
In order to determine whether neonatal mice evidence strong Th1 activity during LM infection, neonatal mice were compared with adult mice with regard to susceptibility to LM, cytotoxic T lymphocyte activity, and cytokine profiles. Neonatal gene profiles relevant to Th1 and Th2 differentiation during LM infection were also compared between neonatal and adult mice, via real-time PCR and RT-PCR.


RESULTS
Neonatal mice were found to be far more susceptible to LM infection than adult mice, due to a lack in the induction of cytotoxic T cell activity, coupled with poor IFN-gamma secretion. Further, LM-infected neonatal mice evidenced much lower levels of expression of Th1-type immune components, including IL-12, IFN-gamma, Delta-4 and T-bet, as compared to those features in adult mice. These results may be due to the comparably lower expressions of mannose-bind lectins and some of toll-like receptors (TLRs) such as TLR-5, -6 and -9, necessary mediators to develop Th1 immune responses.


CONCLUSIONS
Neonatal mice may not mount an adequate Th1 type immune response due to a significantly lower expression of Th1-type immune components as compared to adult mice, even when forced into a Th1-prone environment.
Byun
Hyun-Jung
HJ
Division of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul, South Korea, Republic of Korea.
Jung
Woon-Won
WW
Lee
Jong-Bae
JB
Chung
Hee Yong
HY
Sul
Donggeun
D
Kim
Sang Joon
SJ
Park
Chung-Gyu
CG
Choi
Inho
I
Hwang
Kwang Woo
KW
Chun
Taehoon
T
D000818:Animals; D000831:Animals, Newborn / Q000276:immunology*; D016207:Cytokines / Q000096:biosynthesis / Q000235:genetics; D004195:Disease Models, Animal; D007107:Immune System / Q000502:physiology*; D008089:Listeria monocytogenes / Q000502:physiology*; D008088:Listeriosis / Q000235:genetics / Q000276:immunology* / Q000401:mortality; D051379:Mice; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000378:metabolism; D015996:Survival Rate; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D018417:Th1 Cells / Q000276:immunology*; D018418:Th2 Cells / Q000276:immunology*
D016207:Cytokines; D012333:RNA, Messenger