IL-10 enhances CCL2 release and chemotaxis induced by CCL16 in human monocytes.

CCL16 is a CC chemokine originally identified as a liver-expressed chemokine. Its expression has been detected in activated monocytes where it is up-regulated by stimulation with IL-10. This is in contrast with IL-10's inhibition of the expression of most chemokines. CCL16 is chemotactic for monocytes, lymphocyte and dendritic cells. We investigated whether CCL16 displays biological activities other than chemotaxis and whether IL-10 affects monocyte response to CCL16. We show that CCL16 induces the expression of CCL2 at the mRNA and protein level, but does not affect that of CCL5, CCL18 and proinflammatory cytokines. This effect was prevented by treatment with pertussis toxin and may thus be mediated by G-protein-coupled receptors. IL-10 markedly increased CCL2 production induced by CCL16, but suppressed that of CXCL8. It also enhanced the chemotactic response to CCL16. Addition of antibodies blocking CCR1, but not CCR8, prevented this enhanced chemotactic response and suggested that CCR1 is primarily involved. We propose that IL-10 modulates the effects of CCL16 on monocytes by increasing their CCR1-dependent response. The coordinated secretion of CCL16 and IL-10 may thus enhance monocyte infiltration.

In vitro and in vivo immune stimulating effects of a new standardized Echinacea angustifolia root extract (Polinacea).

Polinacea is a new standardized hydroethanolic extract obtained from Echinacea angustifolia roots containing echinacoside (>4%), the high molecular weight polysaccharide IDN 5405 (>5%) and a isobutylamide fraction (<0.1%). For in vitro tests, a bacterial lipopolysaccharide-free (LPS-free) Polinacea has been prepared in order to avoid non-specific responses of immunocompetent cells. LPS-free Polinacea enhanced the immune functions as highlighted by the proliferation rate and gamma-interferon production in murine T-lymphocyte cell cultures stimulated by anti-CD3. LPS-free Polinacea did not have a direct role on macrophage response as measured in the nitric oxide production test using the J774 macrophage cells line. In vivo, Polinacea showed an immune stimulating activity by reducing the Candida albicans induced mortality both in normal and in cyclosporin A-treated mice.

Expression and role of IL-15 in post-burn hypertrophic scars.

Hypertrophic scarring is a skin disorder that occurs after wounding and thermal injury. There is accumulating evidence that immunologic processes such as infiltration of activated T lymphocytes and altered cytokine production may play a role in the formation of hypertrophic scars. Interleukin-15, a cytokine identified as a T cell growth factor, also acts as a chemoattractant for T cells and has pro-inflammatory properties. We investigated the expression and the role of this cytokine in hypertrophic scarring. IL-15 expression was compared in skin biopsies of hypertrophic scars (HS) both in active (AHS) and in remission (RHS) phases, in normotrophic scars (NTS) and in normal skin using reverse transcriptase-polymerase chain reaction and immunohistochemistry. IL-15 expression in HS was significantly higher than in NTS or normal skin. Furthermore, AHS expressed higher levels of IL-15 than RHS. Immunohistologic analysis of AHS samples showed strong IL-15 immunoreactivity in keratinocytes and Langerhans cells in the epidermis and in macrophages, fibroblasts, and dermal dendritic cells in the dermis. High levels of IL-15 expression in AHS correlated with abundant infiltration of activated CD3+ cells. Ex vivo experiments indicate that IL-15 can sustain the proliferative response of T cells derived from AHS but not from RHS and NTS. In addition, IL-15 prevents both cytokine deprivation and activation-induced apoptosis of T cells derived from AHS. Taken together, these results suggest that IL-15 can be involved in the recruitment, proliferation, and apoptosis inhibition of T cells in AHS. The findings that the evolution from an AHS to a RHS is associated with a decrease in IL15 expression, and with a loss of IL-15 responsiveness in ex vivo-cultured T cells, indicate that this cytokine plays an important role in the biology of pathologic scar formation.

Human monocytes constitutively express membrane-bound, biologically active, and interferon-gamma-upregulated interleukin-15.

Interleukin-15 (IL-15) is a potent regulator of T-, B-, and natural killer cell proliferation and displays unusually tight controls of secretion. Even though IL-15 mRNA is constitutively expressed in monocytes/macrophages and is upregulated by a variety of stimuli, evidence for IL-15 cytokine secretion is only found exceptionally, eg, conditions of pathological, chronic inflammation. This raises the possibility that monocytes express membrane-bound IL-15 rather than secrete it. The current study explores this hypothesis. We demonstrate here that biologically active IL-15 is indeed detectable in a constitutively expressed, membrane-bound form on normal human monocytes, as well as on monocytic cell lines (MONO-MAC-6, THP-1, and U937), but not on human T or B cells (MT4, M9, C5966, JURKAT, DAUDI, RAJI, and Epstein-Barr virus-immortalized B-cell clones). Furthermore, cell surface-bound IL-15 is upregulated upon interferon-gamma stimulation. Interestingly, monocyte/macrophage inhibitory cytokines such as IL-4 and IL-13 fail to downregulate both constitutive and induced cell-surface expression of IL-15. Membrane-bound IL-15 does not elute with acetate buffer or trypsin treatment, suggesting that it is an integral membrane protein and that it is not associated with the IL-15 receptor complex. Finally, membrane-bound IL-15 stimulates T lymphocytes to proliferate in vitro, indicating that it is biologically active. These findings enlist IL-15 in the fairly small family of cytokines for which the presence of a biologically active membrane-bound form has been demonstrated (eg, IL-1, tumor necrosis factor-alpha, and IL-10) and invites the speculation that most of the biological effects of IL-15 under physiological conditions are exerted by the cell surface-bound form.

Interaction of Bartonella henselae with the murine macrophage cell line J774: infection and proinflammatory response.

Bartonella henselae is the causative agent of cat scratch disease (CSD), a self-limiting condition characterized by a subacute regional lymphadenopathy that may develop into disseminated bartonellosis in immunocompromised subjects. Mice experimentally infected with B. henselae display typical liver and spleen granulomas rich in T cells and macrophages. So far there are no data on the interaction between bartonellae and macrophages. In order to clarify this topic, we investigated the interaction of B. henselae with J774, a mouse macrophage cell line. Analysis of bacterial uptake by functional assays and transmission electron microscopy indicates that bartonellae can enter and survive inside J774. Entry occurred within 30 min postinfection and reached a plateau at 160 min. Infection of J774 was followed by a dose-dependent release of the proinflammatory cytokines tumor necrosis factor alpha, interleukin 1beta (IL-1beta), and IL-6. Bartonellae persisted intracellularly without loss of viability for at least 8 h, and their number slightly decreased 24 h postinfection. Gamma interferon (IFN-gamma) treatment of J774 significantly decreased the number of recoverable bacteria at 8 and 24 h. This enhancement of macrophage bactericidal activity was associated with nitric oxide (NO) release and was prevented by the addition of the competitive inhibitor of NO synthesis N(G)-monomethyl L-arginine. These findings suggest that IFN-gamma-mediated activation of macrophages may be important for the clearing of B. henselae infection and that anti-B. henselae microbicidal activity of IFN-gamma-activated macrophages is mediated to a large extent by NO production.