Hepatic interleuklin 15 (IL-15) expression: implications for local NK/NKT cell homeostasis and development - PubMed (original) (raw)

Hepatic interleuklin 15 (IL-15) expression: implications for local NK/NKT cell homeostasis and development

L Golden-Mason et al. Clin Exp Immunol. 2004 Oct.

Abstract

Interleukin 15 (IL-15) is critical for the development of human and murine natural killer (NK) cells and hepatic-derived NK T cells (NKT) in mice, and for the homeostatic maintenance of NK/NKT and CD8(+) memory T cells. The lymphocyte repertoire of an adult human liver includes significant populations of NK and NKT-like cells, which may arise locally from hepatic haematopoietic stem cells (HSCs). We investigated hepatic IL-15 levels and the expression of IL-2/IL-15-receptor beta-chain (IL-2/IL-15Rbeta; CD122) on mature hepatic lymphocytes and HSCs. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect secreted/intracellular IL-15 transcripts. IL-15 protein was localized using immunohistochemistry; levels were measured by enzyme-linked immunosorbent assay IL-2/IL-15Rbeta expression by flow-cytometry. Normal hepatic IL-15 protein was detected at 0.43 ng/100 mg total protein (n = 11, range 0.10 ng-0.9 ng). There was a significant increase in HCV-infected tissue (1.78 ng, P < 0.005, n = 11, range 0.18-2.43 ng). The staining pattern suggests that infiltrating monocytes and tissue resident Kupffer cells are the main producers. IL-15 protein was detected in supernatants from cultured liver biopsy specimens in the absence of stimulation (mean 175.8 pg/100 mg wet tissue, n = 3), which increased significantly upon stimulation (P < 0.05, mean 231.21 pg). On average, 61% of hepatic HSCs expressed IL-2/IL-15Rbeta suggesting a local lymphopoietic role. Eighty per cent of NK and 45.8% of CD56(+) T cells expressed IL-2/IL-15Rbeta, suggesting involvement in local CD56(+) cell activation and expansion. Constitutive expression of IL-15 protein and IL-2/IL-15Rbeta on hepatic lymphocytes suggests a key role in the generation and maintenance of the unique hepatic lymphoid repertoire. The significant increase observed in HCV-infected liver suggests a role for IL-15 in host antiviral responses in the liver.

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Figures

Fig. 1

Levels of interleukin-15 protein in normal liver tissue. Levels of IL-15 protein in hepatic tissue from normal (n = 11), hepatitis C virus (HCV) infected (n = 11) and alcoholic liver disease (ALD, n = 9) were quantified using an ELISA technique. A significant increase in IL-15 (*p < 0·05) was observed for HCV-infected liver (a). Immunohistochemical staining of hepatic tissue showed that IL-15 positive cells in portal tracts have a mononuclear morphology (b). Parenchymal cells staining positively for IL-15 are likely to be Kupffer cells, as they have characteristic cigar-shaped morphology (c). Staining of parenchymal cells was more intense than positively staining portal tract cells, suggesting that Kupffer cells may express more IL-15 than infiltrating monocytes. The isotype-matched negative control is shown in (d).

Fig. 2

Normal liver expresses the secretory isoform of the interleukin-15 gene and secretes IL-15. Electrophoresis on a 2% agarose gel of IL-15-specific PCR products for the nine normal liver samples tested are shown. The upper arrow indicates the 650 bp product and the lower arrow indicates the 524 bp product expressed constitutively in normal liver. The bright band on the 100 bp ladder represents a size of 500 bp. GAPDH controls are also shown (a). Detection of IL-15 in supernatants from three liver biopsies cultured in the absence of exogenous stimulation for 72 h suggested that IL-15 normally produced in liver tissue is secreted. A significant increase in IL-15 production (P < 0·05) is observed in the presence of PMA and ionomycin (b).

Fig. 3

IL-2/IL-15 receptor β-chain expression on hepatic haematopoietic stem cell (HSC) populations. Forward-scatter (size) and side-scatter (granularity) parameters were used to select cells of low to medium granularity (R1) (a). For assessment of the expression of IL-2/IL-15Rβ on hepatic haematopoietic stem cell (HSC) populations CD34+ CD45- (R2) and CD34+ CD45+ (R3) cell populations were gated (b). The level of expression of the receptor relative to isotype-matched control antibody was assayed by histogram analysis (c). Values for each of the individual samples tested are shown (d).

Fig. 4

IL-2/IL-15Rβ positive cells occur more frequently in hepatic CD3 positive T lymphocyte populations than peripheral blood. Total CD3+ and CD56+ hepatic and matched peripheral blood lymphocyte populations were gated. The scatter plot shows the percentage of CD3+/CD56+ cells co-expressing IL-2/IL-15Rβ for blood (○) and liver (□)-derived cells (a). Representative histogram plots of IL-2/IL-15Rβ expression for CD3+ populations are shown for blood (b) and liver (c).

Fig. 5

Increased hepatic T cell IL2/IL-15Rβ expression is due to the presence of high levels of CD3+ CD56+ NT cells. A higher proportion of NKT-like cells co-express IL-2/IL-15Rβ than conventional T cells (a). IL2/IL-15Rβ expression correlated directly with levels of CD3+ CD56+ NKT-like cells (b), thus the higher expression of IL-2/IL-15Rβ on hepatic CD3+ cells may be attributed to the significantly higher proportion of CD56+ T cells in the liver (c).

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Hepatic interleuklin 15 (IL-15) expression: implications for local NK/NKT cell homeostasis and development - PubMed (original) (raw)