Jean S. Marshall

Cutting Edge: Distinct Toll-Like Receptor 2 Activators Selectively Induce Different Classes of Mediator Production from Human Mast Cells

Mast cells play a critical role in host defense against bacterial infection. Murine mast cells produce cytokines in response to bacterial peptidoglycan and LPS via Toll-like receptor (TLR) TLR2- and TLR4-dependent mechanisms. The expression of TLRs by human mast cells and responses to known TLR activators was examined. Human mast cells expressed mRNA for TLR1, TLR2, and TLR6 but not TLR4. Bacterial peptidoglycan and yeast zymosan were potent inducers of GM-CSF and IL-1β and also induced substantial short-term cysteinyl leukotriene generation. In contrast, a synthetic triacylated lipopeptide induced short-term degranulation but failed to induce cysteinyl leukotriene production. The TLR4 activator Escherichia coli LPS did not induce a GM-CSF, IL-1β leukotriene, or degranulation response. These data demonstrate highly selective production of different classes of mast cell mediators in response to distinct TLR activators of potential importance to the host response to bacterial or fungal pathogens.

Dengue Virus Selectively Induces Human Mast Cell Chemokine Production

ABSTRACT Severe dengue virus infections usually occur in individuals who have preexisting anti-dengue virus antibodies. Mast cells are known to play an important role in host defense against several pathogens, but their role in viral infection has not yet been elucidated. The effects of dengue virus infection on the production of chemokines by human mast cells were examined. Elevated levels of secreted RANTES, MIP-1α, and MIP-1β, but not IL-8 or ENA-78, were observed following infection of KU812 or HMC-1 human mast cell-basophil lines. In some cases a >200-fold increase in RANTES production was observed. Cord blood-derived cultured human mast cells treated with dengue virus in the presence of subneutralizing concentrations of dengue virus-specific antibody also demonstrated significantly (P < 0.05) increased RANTES production, under conditions which did not induce significant degranulation. Chemokine responses were not observed when mast cells were treated with UV-inactivated dengue virus in the presence or absence of human dengue virus-specific antibody. Neither antibody-enhanced dengue virus infection of the highly permissive U937 monocytic cell line nor adenovirus infection of mast cells induced a RANTES, MIP-1α, or MIP-1β response, demonstrating a selective mast cell response to dengue virus. These results suggest a role for mast cells in the initiation of chemokine-dependent host responses to dengue virus infection.

Prostaglandin E2 Induces Degranulation-Independent Production of Vascular Endothelial Growth Factor by Human Mast Cells

Mast cells accumulate in large numbers at angiogenic sites, where they have been shown to express a number of proangiogenic factors, including vascular endothelial growth factor (VEGF-A). PGE2 is known to strongly promote angiogenesis and is found in increased levels at sites of chronic inflammation and around solid tumors. The expression pattern of VEGF and the regulation of VEGF-A by PGE2 were examined in cord blood-derived human mast cells (CBMC). CBMC expressed mRNA for five isoforms of VEGF-A and other members of the VEGF family (VEGF-B, VEGF-C, and VEGF-D) with strong expression of the most potent secretory isoforms. PGE2 was a very strong inducer of VEGF-A121/165 production by CBMC and also elevated VEGF-A mRNA expression. The amount of VEGF-A121/165 protein production induced by PGE2 was 4-fold greater than that induced by IgE-mediated activation of CBMC. Moreover, the response to PGE2 as well as to other cAMP-elevating agents such as forskolin and salbutamol was observed under conditions that were not associated with mast cell degranulation. CBMC expressed substantial levels of the EP2 receptor, but not the EP4 receptor, when examined by flow cytometry. In contrast to other reported PGE2-mediated effects on mast cells, VEGF-A121/165 production occurred via activation of the EP2 receptor. These data suggest a role for human mast cells as a potent source of VEGF121/165 in the absence of degranulation, and may provide new opportunities to regulate angiogenesis at mast cell-rich sites.

IgE-Mediated Mast Cell Activation Induces Langerhans Cell Migration In Vivo

Langerhans cells and mast cells are both resident in large numbers in the skin and act as sentinel cells in host defense. The ability of mast cells to induce Langerhans cell migration from the skin to the draining lymph node in vivo was examined. Genetically mast cell-deficient (W/Wv) mice and control mice were sensitized with IgE Ab in the ear pinna. Seven to 14 days later, mice were challenged with Ag i.v. After a further 18–24 h, epidermal sheets and draining auricular lymph nodes were examined using Langerin/CD207 immunostaining. In mast cell-containing mice, a significant decrease in the number of Langerhans cells was observed at epidermal sites of mast cell activation. A significant increase in total cellularity and accumulation of Langerin-positive dendritic cells was observed in the auricular lymph nodes, draining the sites of IgE-mediated mast cell activation. These changes were not observed in W/Wv mice, but were restored by local mast cell reconstitution. Treatment of mast cell-containing mice with the H2 receptor antagonist cimetidine significantly inhibited the observed IgE/Ag-induced changes in Langerhans cell location. In contrast, Langerhans cell migration in response to LPS challenge was not mast cell dependent. These data directly demonstrate the ability of mast cells to induce dendritic cell migration to lymph nodes following IgE-mediated activation in vivo by a histamine-dependent mechanism.

Release of Vasoactive Cytokines by Antibody-Enhanced Dengue Virus Infection of a Human Mast Cell/Basophil Line

ABSTRACT We report here the first demonstration of dengue virus infection and vasoactive cytokine response of a cell of the mast cell/basophil lineage. Infection of KU812 cells was dependent on dengue-specific antibody and gave rise to infectious virions. This antibody-enhanced dengue virus infection triggered a four- to fivefold increase in the release of interleukin-1β (IL-1β) and a modest increase for IL-6 but not for an alternate cytokine, granulocyte-macrophage colony-stimulating factor. The results suggest a potential role for mast cells/basophils in the pathogenesis of dengue virus-induced disease.

Mast Cells Have a Pivotal Role in TNF-Independent Lymph Node Hypertrophy and the Mobilization of Langerhans Cells in Response to Bacterial Peptidoglycan

Peptidoglycan (PGN) from Gram-positive bacteria, activates multiple immune effector cells. PGN-induced lymph node (LN) hypertrophy and dendritic cell mobilization in vivo were investigated following PGN injection into the skin. Both LN activation and the migration of Langerhans cells (LCs) to draining LNs were dependent on the presence of mast cells as demonstrated using mast cell deficient W/Wv mice. However, these responses did not require TLR2, TLR4, or MYD88. TNF-deficient mice exhibited normal increases in LN cellularity but significantly reduced LC migration. In contrast, responses to IgE-mediated mast cell activation were highly TNF dependent. Complement component C3-deficient mice showed decreased LN hypertrophy and abrogated LC migration in response to PGN. These data demonstrate a critical role for mast cells and complement in LN responses to PGN and illustrate a novel TNF-independent mechanism whereby mast cells participate in the initiation of immunity.

Human mast cell activation with virus-associated stimuli leads to the selective chemotaxis of natural killer cells by a CXCL8-dependent mechanism

Human mast cells are found in skin and mucosal surfaces and next to blood vessels. They play a sentinel cell role in immunity, recognizing invading pathogens and producing proinflammatory mediators. Mast cells can recruit granulocytes, and monocytes in allergic disease and bacterial infection, but their ability to recruit antiviral effector cells such as natural killer (NK) cells and T cells has not been fully elucidated. To investigate the role of human mast cells in response to virus-associated stimuli, human cord blood-derived mast cells (CBMCs) were stimulated with polyinosinic.polycytidylic acid, a double-stranded RNA analog, or infected with the double-stranded RNA virus, reovirus serotype 3 Dearing for 24 hours. CBMCs responded to stimulation with polyinosinic.polycytidylic acid by producing a distinct chemokine profile, including CCL4, CXCL8, and CXCL10. CBMCs produced significant amounts of CXCL8 in response to low levels of reovirus infection, while both skin- and lung-derived fibroblasts were unresponsive unless higher doses of reovirus were used. Supernatants from CBMCs infected with reovirus induced substantial NK cell chemotaxis that was highly dependent on CXCL8 and CXCR1. These results suggest a novel role for mast cells in the recruitment of human NK cells to sites of early viral infection via CXCL8.

Prostaglandin E2 Selectively Enhances the IgE-Mediated Production of IL-6 and Granulocyte-Macrophage Colony-Stimulating Factor by Mast Cells Through an EP1/EP3-Dependent Mechanism

PGE2 is an endogenously synthesized inflammatory mediator that is over-produced in chronic inflammatory disorders such as allergic asthma. In this study, we investigated the regulatory effects of PGE2 on mast cell degranulation and the production of cytokines relevant to allergic disease. Murine bone marrow-derived mast cells (BMMC) were treated with PGE2 alone or in the context of IgE-mediated activation. PGE2 treatment alone specifically enhanced IL-6 production, and neither induced nor inhibited degranulation and the release of other mast cell cytokines, including IL-4, IL-10, IFN-γ, and GM-CSF. IgE/Ag-mediated activation of BMMC induced the secretion of IL-4, IL-6, and GM-CSF, and concurrent PGE2 stimulation synergistically increased mast cell degranulation and IL-6 and GM-CSF, but not IL-4, production. A similar potentiation of degranulation and IL-6 production by PGE2, in the context of IgE-directed activation, was observed in the well-established IL-3-dependent murine mast cell line, MC/9. RT-PCR analysis of unstimulated MC/9 cells revealed the expression of EP1, EP3, and EP4 PGE receptor subtypes, including a novel splice variant of the EP1 receptor. Pharmacological studies using PGE receptor subtype-selective analogs showed that the potentiation of IgE/Ag-induced degranulation and IL-6 production by PGE2 is mediated through EP1 and/or EP3 receptors. Our results suggest that PGE2 may profoundly alter the nature of the mast cell degranulation and cytokine responses at sites of allergic inflammation through an EP1/EP3-dependent mechanism.

Human Mast Cells Transmigrate Through Human Umbilical Vein Endothelial Monolayers and Selectively Produce IL-8 in Response to Stromal Cell-Derived Factor-1α

Mature mast cells are generally considered to be less mobile cells residing within tissue sites. However, mast cell numbers are known to increase in the context of inflammation, and mast cells are recognized to be important in regulating local neutrophil infiltration. CXC chemokines may play a critical role in this process. In this study two human mast cell-like lines, HMC-1 and KU812, and human cord blood-derived primary cultured mast cells were employed to examine role of stromal cell-derived factor-1 (SDF-1) in regulating mast cell migration and mediator production. It was demonstrated that human mast cells constitutively express mRNA and protein for CXCR4. Stimulation of human mast cells with SDF-1, the only known ligand for CXCR4, induced a significant increase in intracellular calcium levels. In vitro, SDF-1α mediated dose-dependent migration of human cord blood-derived mast cells and HMC-1 cells across HUVEC monolayers. Although SDF-1α did not induce mast cell degranulation, it selectively stimulated production of the neutrophil chemoattractant IL-8 without affecting TNF-α, IL-1β, IL-6, GM-CSF, IFN-γ, or RANTES production, providing further evidence of the selective modulation of mast cell function by this chemokine. These findings provide a novel, SDF-1-dependent mechanism for mast cell transendothelial migration and functional regulation, which may have important implications for the local regulation of mast cells in disease.

A Th1-inducing adjuvant, MPL, enhances antibody profiles in experimental animals suggesting it has the potential to improve the efficacy of allergy vaccines.

Background: Monophosphoryl lipid A (MPL®) is a detoxified derivative of the lipopolysaccharide (LPS) moiety of Salmonella minnesota R595, which has retained immunostimulatory activities. MPL® has been administered to many subjects in clinical trials as an adjuvant component of infectious disease vaccines and is currently a component of a licensed cancer vaccine, Melacine® (Corixa Inc., Schering Plough). MPL® has, in particular, been shown to promote Th1-type antigen specific responses. L-tyrosine is a depot adjuvant which is fully metabolisable and has been successfully employed in allergy vaccines for a number of years. Methods: Mice were immunised with MPL® adjuvant in conjunction with separate preparations of either ovalbumin or glutaraldehyde-modified ragweed pollen extract both coprecipitated with L-tyrosine. The specific antibody isotypes IgG1, IgG2a, IgG2b and also IgE were measured. Rats received booster injections of keyhole limpet haemocyanin (KLH) in conjunction with MPL® adjuvant following priming with KLH in alum alone. KLH-specific antibody responses were measured. Results: It was shown that a combination of L-tyrosine and MPL® were synergistic in enhancing murine antigen specific IgG antibody responses without enhancing antigen specific IgE responses. Furthermore, this adjuvant combination promoted strong IgG2 antigen specific responses indicative of a Th1 directed response. In KLH sensitised rats, treatment with MPL® was shown to prevent a secondary IgE antibody response when injected with booster injections of antigen. Conclusions: Immunisation of mice with two different antigens adsorbed to L-tyrosine induced a Th1-skewed primary response when in conjunction with MPL® adjuvant which also generally enhances a specific IgG response. Incorporation of MPL® adjuvant in the immunisation of rats prevented a secondary specific IgE response. These results suggest that the employment of this new adjuvant in clinical allergy vaccination formulations may result in an improved efficacy which could be utilised in various ways to improve compliance.