Interleukin-1beta selectively expands and sustains interleukin-22+ immature human natural killer cells in secondary lymphoid tissue.

Among human natural killer (NK) cell intermediates in secondary lymphoid tissue (SLT), stage 3 CD34(-)CD117(+)CD161(+)CD94(-) immature NK (iNK) cells uniquely express aryl hydrocarbon receptor (AHR) and interleukin-22 (IL-22), supporting a role in mucosal immunity. The mechanisms controlling proliferation and differentiation of these cells are unknown. Here we demonstrate that the IL-1 receptor IL-1R1 was selectively expressed by a subpopulation of iNK cells that localized proximal to IL-1beta-producing conventional dendritic cells (cDCs) within SLT. IL-1R1(hi) iNK cells required continuous exposure to IL-1beta to retain AHR and IL-22 expression, and they proliferate in direct response to cDC-derived IL-15 and IL-1beta. In the absence of IL-1beta, a substantially greater fraction of IL-1R1(hi) iNK cells differentiated to stage 4 NK cells and acquired the ability to kill and secrete IFN-gamma. Thus, cDC-derived IL-1beta preserves and expands IL-1R1(hi)IL-22(+)AHR(+) iNK cells, potentially influencing human mucosal innate immunity during infection.

The Axl/Gas6 pathway is required for optimal cytokine signaling during human natural killer cell development.

Interleukin-15 (IL-15) is essential for natural killer (NK) cell differentiation. In this study, we assessed whether the receptor tyrosine kinase Axl and its ligand, Gas6, are involved in IL-15-mediated human NK differentiation from CD34(+) hematopoietic progenitor cells (HPCs). Blocking the Axl-Gas6 interaction with a soluble Axl fusion protein (Axl-Fc) or the vitamin K inhibitor warfarin significantly diminished the absolute number and percentage of CD3(-)CD56(+) NK cells derived from human CD34(+) HPCs cultured in the presence of IL-15, probably resulting in part from reduced phosphorylation of STAT5. In addition, CD3(-)CD56(+) NK cells derived from culture of CD34(+) HPCs with IL-15 and Axl-Fc had a significantly diminished capacity to express interferon-gamma or its master regulator, T-BET. Culture of CD34(+) HPCs in the presence of c-Kit ligand and Axl-Fc resulted in a significant decrease in the frequency of NK precursor cells responding to IL-15, probably the result of reduced c-Kit phosphorylation. Collectively, our data suggest that the Axl/Gas6 pathway contributes to normal human NK-cell development, at least in part via its regulatory effects on both the IL-15 and c-Kit signaling pathways in CD34(+) HPCs, and to functional NK-cell maturation via an effect on the master regulatory transcription factor T-BET.

Homeostatic cytokines and expansion of regulatory T cells accompany thymic impairment in children with Down syndrome.

Down syndrome (DS), the most common chromosomal abnormality in humans, is characterized by precocious immunologic aging that results, among other things, in alterations of B and T lymphocyte subsets and natural killer cells, defective phagocytosis, and chemotaxis of polymorphonuclear leukocytes. We studied 30 children affected by DS, compared them to 29 healthy controls, and evaluated the functionality of the thymus (by measuring the amount of lymphocytes that express the signal-joint T cell receptor rearrangement excision circles [sj-TREC+]), the plasma levels of interleukin (IL)-7 and IL-15, the proliferative T cell response to these cytokines, the expression of the alpha chain of the IL-7 receptor (CD127), the extrathymic differentiation of T lymphocytes, and the presence of natural regulatory T cells (Tregs) in peripheral blood. We found that DS children had a significantly lower number of sj-TREC+ lymphocytes, the levels of which were strongly correlated with age. We found higher plasma levels of IL-7 and IL-15 than in healthy controls, and a higher proliferative T cell response to IL-15. DS children also showed a lower percentage of CD4(+) cells and profound alterations of T cell differentiation, along with increased amount of Tregs and of cells expressing markers of apoptosis. We can thus hypothesize that the precocious thymic involution occurring in DS is mirrored by a high production of IL-7 and IL-15, which is crucial for cell survival and proliferation. The complex alterations present in the periphery are likely the result of a compensatory mechanism: the overproduction of homeostatic cytokines could be a reaction to the impaired intrathymic production of T lymphocytes and/or to the expansion of Treg in the periphery, and could be required to allow the survival of T cells.

Mitochondrial alterations and tendency to apoptosis in peripheral blood cells from children with Down syndrome.

Different types of cells from subjects with Down syndrome (DS) have an increased susceptibility to cell death. We have studied apoptosis and mitochondrial (mt) membrane potential (DeltaPsi(m)) in peripheral blood mononuclear cells (PBMC) from DS children and age-matched healthy donors after in vitro treatment with apoptogenic molecules, along with mtDNA content. We found that PBMC from DS and healthy controls had a similar tendency to undergo apoptosis and a similar amount of mtDNA. However, in cells from DS subjects, mitochondria showed a higher loss of DeltaPsi(m), underlying the presence of an increasing susceptibility of these organelles to damaging agents.

Altered mitochondrial RNA production in adipocytes from HIV-infected individuals with lipodystrophy.

BACKGROUND: Damage to mitochondria (mt) is a major side effect of highly active antiretroviral therapy (HAART) that includes a nucleoside reverse transcriptase inhibitor (NRTI). Such damage is associated with the onset of lipodystrophy in HAART-treated HIV+ patients. To further investigate mt changes during this syndrome, we analysed the expression of mtRNA in adipocytes from lipodystrophic HIV+ patients taking NRTI-containing HAART and compared it with similar cells from healthy individuals. MATERIALS AND METHODS: Total RNA was extracted from adipocytes collected from different anatomical locations of 11 HIV+ lipodystrophic patients and seven healthy control individuals. RNA was reverse transcribed and Taqman-based real-time PCR was used to quantify three different mt transcripts (ND1, CYTB and ND6 gene products). mtRNA content was normalized versus the housekeeping transcript L13. RESULTS: ND1, CYTB and ND6 expression was significantly reduced in HIV+ lipodystrophic patients. HIV+ men and women did not differ in a statistically significant way regarding the levels of ND1 and ND6, whereas the opposite occurred for CYTB. CONCLUSIONS: Lipodystrophy following treatment with NRTI-containing HAART is associated with a decrease in adipose tissue mtRNAs.