Differential expression of the cytokine receptors for human interleukin (IL)-12 and IL-18 on lymphocytes of both CD45RA+ and CD45RO+ phenotype from tonsils, cord and adult peripheral blood

The objective of this study was to demonstrate the variable expression of cytokine receptors on naive versus memory human CD4(+) T cell subpopulations in tonsillar tissue, cord blood and adult blood. We prove that the receptors for both interleukin (IL)-12 and IL-18 are expressed exclusively on memory T cells. This observation was seen not only on the CD45RO(+) memory T cells but also on a significant percentage of the CD45RA(+), CD62L(-), CD27(-) and CCR7(-) populations. Furthermore, CD45RA(+) CD62L(+), CD27(+) or CCR7(+) CD4(+) T cells that expressed IL-12Rbeta1 and IL-18Ralpha did not express CD31, a marker for recent thymic emigrants. We reveal that cord blood lymphocytes do not express IL-12Rbeta1 whereas IL-18Ralpha expression was detected at low levels. Importantly, the IL-12Rbeta2 signalling chain, which is absent in all resting T cells, was up-regulated in both CD45RA(+) and CD45RO(+) T cells as a result of stimulation with anti-CD3 and anti-CD28 in vitro. This observed up-regulation was, however, restricted to 80% of the total CD4(+) population. Finally, a very small proportion of the CD4(+) CD45RO(+) tonsillar T cells expressed the IL-12 and IL-18 receptors, thereby establishing the differential expression of these receptors between peripheral and tonsillar memory T cell subpopulations.