Expression and Function of Toll-like Receptors in Lymphocytes from Human Neonates.

Author: Pallave Dasari

Dasari, Pallave, 2011 Expression and Function of Toll-like Receptors in Lymphocytes from Human Neonates., Flinders University, School of Medicine

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Neonates have high global rates of morbidity and mortality due to infectious diseases; this susceptibility is attributed to the immaturity of the neonatal immune response. The immune system of neonates, compared to adults, has reduced function in several aspects of immunity and lacks the long-term memory response. Toll-like receptors (TLR) are a family of pattern recognition receptors which bind various microbial components and alert the immune system to invading pathogens. Comparing TLR expression and function in neonatal lymphocytes and adult lymphocytes may reveal how TLR influence these immune cells in early life. Due to the immaturity of their immune responses, neonates may be more reliant on TLR for protection against infection. The extracellular and intracellular expression of TLR1, TLR2, TLR3, TLR4, TLR6, TLR8 and TLR9 was examined on non-stimulated and stimulated T lymphocytes and B lymphocytes from cord blood, adult peripheral blood and tonsils from human subjects. B lymphocytes were categorised into subsets to see if differentiation stage of B lymphocytes affects TLR expression. The responses of purified B lymphocytes, from neonates, adults and tonsils, to ligands of TLR3, TLR4, TLR8 and TLR9 were compared. The functions measured were proliferation, levels of total Ig, IgG and IgM, and levels of IL-6 and IL-8. Tonsil B lymphocytes were tested for expression of activation markers (CD23, CD25, CD69 and HLA-DR), co-stimulatory molecules (CD40, CD80 and CD86), and CD21 and CD210. The TLR expression patterns by T lymphocytes and B lymphocytes were similar between neonates and adults, and stimulation of lymphocytes had little effect on TLR expression. T lymphocytes from neonates and adults expressed TLR2, TLR3, TLR4, TLR8 and TLR9. B lymphocytes from neonates and adults expressed TLR1, TLR3, TLR4, TLR8 and TLR9. B lymphocytes from tonsils expressed TLR3, TLR4, TLR8 and TLR9. Cellular location of TLR was mostly consistent with the literature, except for detection of TLR4 in permeabilised cells and TLR8 on non-permeabilised cells. CpG ODN, TLR9 ligand, induced strong proliferation, secretion of total Ig, IgG, IgM and IL-6 from B lymphocytes from neonates, adults and tonsils. Adult B lymphocytes produced higher levels of total Ig, IgM and IL-6 in response to the other TLR ligands compared to neonatal and tonsil B lymphocytes. IL-8 levels were unaffected by TLR ligands in neonates, adults and tonsils. Neonatal lymphocytes have adult-like capacity to "innately" recognise foreign pathogens. Neonatal B lymphocytes have reduced responses to TLR ligands compared to adult B lymphocytes. However, neonatal B lymphocytes respond to TLR ligands, especially CpG ODN, with increased functions. TLR agonists, particularly CpG ODN, are potentially strong candidates for future research in neonatal vaccinology.

Keywords: toll like receptors,lymphocytes,neonates,cpg odn,tonsils,cord blood,blood
Subject: Paediatrics and Child Health thesis, Medicine thesis

Thesis type: Doctor of Philosophy
Completed: 2011
School: School of Medicine
Supervisor: Heddy Zola