Co-Expression of TLR2 and CCR5 on Human T cells

Evidence has emerged for a subpopulation of human T cells that express TLR2, a pattern recognition receptor ordinarily found on innate immune cells. A cross-modulation pathway between TLR2 and CCR5, a chemokine receptor involved in cell migration, has been reported in human monocytes by the Signoret lab. CCR5 is expressed by several subsets of T cells and notably takes part in the pathogenesis of cancer and HIV-1 infection. Whilst a TLR2/CCR5 double-expressing T cell population has been previously reported, its function is unclear, and the possibility of a TLR2/CCR5 communication pathway is yet to be explored. Expansion of this population could allow functional characterisation, and elucidate the conditions favouring generation of these cells.
Frozen monocyte-depleted human PBMCs were expanded using 9-day PHA/IL2
stimulation. TLR2+ T cells were identified by flow cytometry, and were characterised as a
mixed population of TLR2+ CD25+ cells that can also express CCR5, CD4, CD8, CD45RO
and FoxP3. This subpopulation was detected after three days of PHA stimulation, but
could not be expanded in presence of IL2 and disappeared from culture by day 9,
suggesting a transient cell phenotype. These experiments were repeated with a cell
preparation from freshly isolated PBMCs; the same subpopulation could be identified, but
the results suggest that the majority of TLR2+CD25+ cells are also CD45RO+ and CCR5+.
Following a literature review, alternative stimulation conditions thought to favour TLR2
expression were tested. As with PHA/IL2, no significant expansion of the TLR2+ CCR5+
subpopulation was observed. A downmodulation experiment was carried out assessing
the impact of TLR2 and CCR5 specific ligands on the cell surface expression of their
receptors. TLR2 ligand stimulation did not affect CCR5 cell surface levels, indicating that
receptor regulation on these cells may differ from that of monocytes. However, further
experiments should be carried out before conclusions are drawn.