Human CD4+ T cell clones produce and release nerve growth factor and express high-affinity nerve growth factor receptors.

BACKGROUND: Increasing evidence shows that nerve growth factor (NGF) plays a role
in the complex and fascinating linkage between the nervous and the immune systems
due to its ability to modulate functions of several inflammatory cells.
OBJECTIVE: To investigate NGF receptor expression and NGF production and release
by human CD4+ cells clones, which have primary relevance in modulating
inflammatory events through their different subsets of functional phenotypes.
METHODS: The expression of NGF and a transmembrane tyrosine kinase (TrkA) was
evaluated by immunohistochemistry and flow cytometry analysis in five T(H0), six
T(H1), and five T(H2) cell clones derived from human circulating mononuclear
blood cells. Moreover, the amount of NGF protein was assessed by measuring the
NGF levels in culture supernatants of the T cell clones before stimulation and 48
hours after phytohemagglutinin (PHA) activation by use of an immunoenzymatic
assay.
RESULTS: Our data have shown that in unstimulated conditions, human CD4+ T cell
clones express both immunoreactivity for NGF and the TrkA NGF receptor
irrespective of their cytokine profile. Moreover, T(H1) and T(H2) clones, but not
T(H0) clones, secrete NGF in basal conditions. PHA activation induces NGF
secretion in T(H0) clones and a significant increase of NGF levels in T(H2) (p <
0.05), but not in T(H1) culture supernatants.
CONCLUSIONS: Results obtained represent the first evidence of TrkA expression and
NGF production and release in human CD4+ cell clones and suggest a possible
functional role of NGF in modulating the immune and inflammatory network.