Induction of cytotoxic CD8+CD56+ T cells from human thymocytes by interleukin-15.

CD8(+) CD56(+) cells isolated from human peripheral blood lymphocytes have been shown recently to represent a population of cytotoxic active T cells. However, it is not known if these cells are intrathymically or extrathymically developed or how these cells are influenced by growth factors. In the present study, we investigated the effects of interleukin-2 (IL-2) and IL-15 on human thymocytes with respect to development of CD8(+) CD56(+) T cells. Freshly isolated thymocytes contain few CD8(+) CD56(+) cells, but the number of these cells increases significantly when thymocytes are grown in the presence of IL-15 or IL-2. However, IL-15 induced a significantly higher fraction of CD8(+) CD56(+) cells compared with IL-2. Thus, although IL-2 and IL-15 are known to have a number of redundant functions, we here demonstrate that IL-15 is superior to IL-2 in inducing CD8(+) CD56(+) T cells from cultures of thymocytes. The majority of the IL-15-grown CD8(+) CD56(+) cells were CD45R0(+), representing a memory phenotype, and showed high expression of the IL-15R-complex and high numbers of CD69(+) cells. Moreover, cytotoxic activity was confined to this cell population.

Dipeptidyl peptidase IV inhibition enhances the intestinotrophic effect of glucagon-like peptide-2 in rats and mice.

Glucagon-like peptide-2 (GLP-2) induces intestinal growth in mice; but in normal rats, it seems less potent, possibly because of degradation of GLP-2 by the enzyme dipeptidyl peptidase IV (DPP-IV). The purpose of this study was to investigate the survival and effect of GLP-2 in rats and mice after s.c. injection of GLP-2 with or without the specific DPP-IV inhibitor, valine-pyrrolidide (VP). Rats were injected s.c. with 40 microg GLP-2 or 40 microg GLP-2+15 mg VP. Plasma was collected at different time points and analyzed, by RIA, for intact GLP-2. Rats were treated for 14 days with: saline; 15 mg VP; 40 microg GLP-2, 40 microg GLP-2+15 mg VP; 40 microg GLP-2 (3-33). Mice were treated for 10 days with: saline; 5 microg GLP-2; 5 microg GLP-2+1.5 mg VP; 25 microg GLP-2; 25 microg GLP-2 (3-33). In both cases, body weight, intestinal weight, length, and morphometric data were measured. After s.c. injection, the plasma concentration of GLP-2 reached a maximum after 15 min, and elevated concentrations persisted for 4-8 h. With VP, the concentration of intact GLP-2 was about 2-fold higher for at least the initial 60 min. Rats treated with GLP-2+VP had increased (P < 0.01) small-bowel weight (4.68 +/- 0.11%, relative to body weight), compared with the two control groups, [3.01 +/- 0.06% (VP) and 2.94 +/- 0.07% (NaCl)] and GLP-2 alone (3.52 +/- 0.10%). In mice, the growth effect of 5 microg GLP-2+VP was comparable with that of 25 microg GLP-2. GLP-2 (3-33) had no effect in rats, but it had a weak effect on intestinal growth in mice. The extensive GLP-2 degradation in rats can be reduced by VP, and DPP-IV inhibition markedly enhances the intestinotrophic effect of GLP-2 in both rats and mice. We propose that DPP-IV inhibition may be considered to enhance the efficacy of GLP-2 as a therapeutic agent.

Interleukin 15 is a growth factor for human thymocytes with preferential effect on CD8(+)cells.

The effects of IL-15, as compared to IL-2, on growth of human thymocytes has been evaluated. Expression of comparable amounts of receptor chains was found on IL-2 and IL-15 cultured thymocytes, as well as comparable receptor signalling. However, IL-15 was superior to IL-2 in promoting CD8(+)thymocyte growth, whereas CD4(+)cells proliferated to a higher extent in IL-2 cultures. CD4(+)8(+)and CD4(-)8(-)thymocytes expanded equally well in both culture types.

Superantigens are presented by and activate thymocytes from infants.

A high percentage of human fetal and postnatal thymocytes express MHC class II molecules. This raises the possibility that human thymocytes in early life are able to present peptides to other immature T cells and thereby initiate thymic selection of these cells. Here we address this question by exposing newly harvested infant thymocytes to superantigen (Sag) which binds to the T-cell receptor and to MHC class II chains outside the peptide binding groove. The results show that the thymocytes are able to present Sag and to be activated to proliferation as well as apoptosis by Sag presented by other thymocytes. The absence of responses to Sag with mutations in class II binding sites showed that class II molecules were necessary for the responses, and very low expression of class II molecules on CD4-8- cells indicates that the demonstrated T-cell/T-cell interactions are confined to T-cell receptor-positive CD4+8+, CD4+8-, and CD4-8+ cells. These latter subsets were shown to be able to present Sag to each other. These findings suggest that class II+ thymocytes may participate in the selection of self-restricted T cells during a critical period in the shaping of the human immune system.