Interleukin-15 (IL-15) is a novel cytokine with actions similar to IL-2 because of common receptor components. Although IL-15 is expressed in colonic epithelial cells and may regulate epithelial cell function, its effects on these cells are not fully defined. We explored the regulatory effects of IL-15 on IL-8 and monocyte-chemoattractant protein-1 (MCP-1) production in the colonic epithelial cell line Caco-2 as well as in freshly isolated human colonic epithelial cells. IL-15 was added to intestinal epithelial cells under various culture conditions. Levels of chemokines were determined by enzyme-linked immunosorbent assay. To determine the elements of the IL-2/IL-15R complex involved we used neutralizing antibodies specific for individual receptor chains. IL-15 down-regulates IL-8 and MCP-1 production in Caco-2 cells as well as in freshly isolated human colonic epithelial cells in a dose-dependent manner. Intestinal epithelial cells became more responsive to IL-15-induced suppression when activated with greater IL-1 doses. Strong chemokine suppression was seen when IL-15 was given prior to, simultaneous with, or after stimulatory agent. Anti-IL-2Rgamma antibodies efficiently blocked (82% inhibition) the suppression induced by IL-15, while anti-IL-2Rbeta antibodies were less effective. The involvement of beta-chain was further suggested by the finding that a mixture of both monoclonal antibodies (mAb) at a suboptimal concentration (1 microgram/ml of each mAb) produced a synergistic inhibitory effect on down-regulation of epithelial chemokine production. These results show that IL-15 can suppress IL-8 and MCP-1 secretion by intestinal epithelial cells. A microenvironment containing high concentrations of IL-15 may alter the recruitment of neutrophils to enterocytes at least partly by inhibiting IL-8 and MCP-1 production.

To investigate whether antigen-independent, interleukin-2 (IL-2) or IL-15 activation of polarized T helper (Th) cells would result in contact-dependent activation of monocytes, living Th1 and Th2 cell clones were co-cultured with THP-1 cells or fresh peripheral blood monocytes. Under these conditions IL-1beta production was induced almost exclusively by Th1 cells and was dependent on the presence and dose of IL-2 or IL-15, and on cell-cell contact, as demonstrated by double-chamber cultures. Low levels of IL-1 receptor antagonist (IL-1Ra) were induced by Th1 and higher levels by Th2 cells. IL-10 production was similar in Th1/monocyte and Th2/monocyte co-cultures, thus arguing against preferential down-regulation of IL-1beta production by anti-inflammatory IL-10 in Th2 co-cultures. In addition, IL-4 and IL-10 neutralization did not result in enhanced IL-1beta production in Th2/monocyte co-cultures. Preferential expression on Th1 cells of CD11b correlated with their capacity to induce IL-1beta production by THP-1 cells in the presence of IL-2 or IL-15, but anti-CD11b monoclonal antibody could not inhibit this activity. Blockade of the CD40-CD40 ligand interaction resulted in inhibition of IL-1beta-inducing capacity while IL-1Ra induction was unaffected, a result previously unknown. This differential effect indicates the selective relevance of CD40-CD40 ligand engagement in inflammatory monocyte responses upon activation by T cells. CD40 ligand expression levels did not differ in Th1 and Th2 cell clones, thus indicating that additional, unidentified molecule(s) preferentially expressed by Th1 cells are involved in their IL-1beta induction capacity.

Interleukin-15 (IL-15) is a pro-inflammatory cytokine thought to contribute to the inflammation in inflammatory bowel diseases (IBD). The specific receptor chain IL-15Rα can be expressed as a transmembranous signalling receptor, or can be cleaved by a disintegrin and metalloprotease domain 17 (ADAM17) into a neutralizing, soluble receptor (sIL-15Rα). The aim of this study is to evaluate the expression of IL-15Rα in ulcerative colitis (UC) and Crohn's disease (CD) patients before and after infliximab (IFX) therapy. Gene expression of IL-15Rα, IL-15 and ADAM17 was measured at the mRNA level by quantitative reverse transcription-PCR in mucosal biopsies harvested before and after first IFX therapy. Concentrations of sIL-15Rα were measured in sera of patients by ELISA and IL-15Rα protein was localized in the gut by immunohistochemistry and immunofluorescence. Mucosal expression of IL-15Rα is increased in UC and CD patients compared with controls and it remains elevated after IFX therapy in both responder and non-responder patients. The concentration of sIL-15Rα in serum is also increased in UC patients when compared with controls and does not differ between responders and non-responders either before or after IFX. CD patients have levels of sIL-15Rα comparable to healthy controls before and after therapy. In mucosal tissues, IL-15Rα(+) cells closely resemble activated memory B cells with a pre-plasmablastic phenotype. To conclude, IBD patients have an increased expression of IL-15Rα mRNA in the mucosa. Expression is localized in B cells, suggesting that IL-15 regulates B-cell functions during bowel inflammation. No change in release of sIL-15Rα is observed in patients treated with IFX.

Vitamins A and E and select flavonoids in the family of catechins are well-defined small molecules that, if proven to possess immunomodulatory properties, hold promise as vaccine adjuvants and various therapies. In an effort to determine the in vivo immunomodulatory properties of these molecules, we found that although mucosal and systemic vaccinations with a recombinant HIV-1BaL gp120 with either a catechin, epigallo catechin gallate (EGCG) or pro-vitamin A (retinyl palmitate) alone in a vegetable-oil-in-water emulsion (OWE) suppressed antigen-specific responses, the combination of EGCG and vitamin A or E in OWE (Nutritive Immune-enhancing Delivery System, NIDS) synergistically enhanced adaptive B-cell, and CD4(+) and CD8(+) T-cell responses, following induction of relatively low local and systemic innate tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-17, but relatively high levels of early systemic IL-15 responses. For induction of adaptive interferon-γ and TNF-α responses by CD4(+) and CD8(+) T cells, the adjuvant effect of NIDS was dependent on both IL-15 and its receptor. In addition, the anti-oxidant activity of NIDS correlated positively with higher expression of the superoxide dismutase 1, an enzyme involved in reactive oxygen species elimination but negatively with secretion of IL-1β. This suggests that the mechanism of action of NIDS is dependent on anti-oxidant activity and IL-15, but independent of IL-1β and inflammasome formation. These data show that this approach in nutritive vaccine adjuvant design holds promise for the development of potentially safer effective vaccines.

Natural killer (NK) cells are important components of the innate immune system that mediate effector and regulatory functions. As effector cells, NK cells help control virus-infected cells through cell-mediated antibody-dependent mechanisms such as antibody-dependent cellular cytotoxicity (ADCC). Although macaques are an important and reliable animal model for the study of retrovirus-induced human diseases, and despite the crucial role played by NK cells in innate and adaptive immune responses against simian immunodeficiency virus (SIV), only a few studies have attempted to characterize different macaque NK cell subpopulations. In the present study, we identified a subpopulation of circulatory CD8α(-) macaque NK cells that express NK lineage markers and exhibit cytotoxic potential. CD8α(-) NK cells were phenotypically characterized as CD3(-) CD14(-) CD20(-) CD8α(-) cells that express NK cell markers including CD16, CD56, granzyme B, perforin, NKG2D and KIR2D. Based on their CD56/CD16 expression patterns, cells within the CD8α(-) gate can be divided into four subpopulations: CD56(dim) CD16(bright) , CD56(dim) CD16(-) , CD56(bright) CD16(-) , and CD56(-) CD16(-) cells. In contrast, CD8α(+) NK cells are 95% CD56(dim) CD16(bright) , which correlates with their high cytotoxic potential. Upon interleukin-15 activation, CD8α(-) cells up-regulated CD69 expression and produced low levels of interferon-γ and tumour necrosis factor-α. Sorted CD8α(-) NK cells were capable of killing MHC-I-devoid target cells and mediated ADCC responses against SIV gp120-coated target cells in the presence of macaque anti-gp120 antibodies. Taking into account CD8α(-) myeloid dendritic cells, we show that about 35% of macaque CD8α(-) cells represent a novel, functional population of circulatory NK cells that possesses cytotoxic potential and is capable of mediating anti-viral immune responses.