Kenneth H. S. Wong

Predominance of subtype 3 among Blastocystis isolates from a major hospital in Singapore

Blastocystis is an enteric protozoan parasite commonly found in humans and animals. Phylogenetic and genotypic analyses have shown that Blastocystis exhibits extreme genetic diversity, and humans are host to a number of zoonotic isolates. In the present study, the prevalence of Blastocystis in 276 stool samples from a hospital in Singapore was examined, and for the first time, riboprinting using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to determine the genetic diversity of the Blastocystis isolated from the Singapore population. The prevalence rate was determined to be 3.3% (9/276), and Blastocystis displaying two main ribotypes were isolated. As a comparison, we performed PCR-RFLP using two different published methodologies, and both methods allowed the isolates to be divided into two distinct groups based on their riboprint patterns. According to a recently proposed classification scheme, 78% (7/9) of the isolates were of subtype 3, while 22% (2/9) were subtype 1. The predominance of subtype 3 in an urbanized city state such as Singapore is in agreement with the idea that subtype 3 is a genotype of human origin.

NK Cells Regulate CD8+ T Cell Priming and Dendritic Cell Migration during Influenza A Infection by IFN-γ and Perforin-Dependent Mechanisms

An effective immune response against influenza A infection depends on the generation of virus-specific T cells. NK cells are one of the first-line defenses against influenza A infection. We set out to delineate the role of NK cells in T cell immunity using a murine model of influenza A infection with A/PR/8/34. We show that early T cell recruitment mainly occurs in the posterior mediastinal lymph node (pMLN). Depletion of NK cells significantly impaired both dendritic cell (DC) and T cell recruitment into the pMLN. A similar reduction of T cell recruitment was observed when migration was blocked by pertussis toxin, suggesting that migration of pulmonary NK cells and DCs regulates cell recruitment to the pMLN. T cell recruitment was dependent on IFN-γ, and transfer of IFN-γ–competent naive NK cells into IFN-γ−/− mice restored T cell recruitment, whereas IFN-γ–deficient NK cells failed to do so. In addition, NK cell depletion reduced the uptake and transport of influenza A virus by DCs, and significantly impaired the virus-specific T cell response. Both IFN-γ−/− and perforin−/− mice showed reduced viral Ag transport by DCs, suggesting that the ability of NK cells to influence virus transport depends on IFN-γ and perforin. In summary, our data suggest that NK cells play a critical role in the initiation and shaping of the T cell response after influenza A infection.

GM-CSF–Licensed CD11b+ Lung Dendritic Cells Orchestrate Th2 Immunity to Blomia tropicalis

The Blomia tropicalis dust mite is prevalent in tropical and subtropical regions of the world. Although it is a leading cause of asthma, little is known how it induces allergy. Using a novel murine asthma model induced by intranasal exposure to B. tropicalis, we observed that a single intranasal sensitization to B. tropicalis extract induces strong Th2 priming in the lung draining lymph node. Resident CD11b+ dendritic cells (DCs) preferentially transport Ag from the lung to the draining lymph node and are crucial for the initiation of Th2 CD4+ T cell responses. As a consequence, mice selectively deficient in CD11b+ DCs exhibited attenuated Th2 responses and more importantly did not develop any allergic inflammation. Conversely, mice deficient in CD103+ DCs and CCR2-dependent monocyte-derived DCs exhibited similar allergic inflammation compared with their wild-type counterparts. We also show that CD11b+ DCs constitutively express higher levels of GM-CSF receptor compared with CD103+ DCs and are thus selectively licensed by lung epithelial-derived GM-CSF to induce Th2 immunity. Taken together, our study identifies GM-CSF–licensed CD11b+ lung DCs as a key component for induction of Th2 responses and represents a potential target for therapeutic intervention in allergy.

Gamma Interferon Regulates Contraction of the Influenza Virus-Specific CD8 T Cell Response and Limits the Size of the Memory Population

ABSTRACT The factors that regulate the contraction of the CD8 T cell response and the magnitude of the memory cell population against localized mucosal infections such as influenza are important for generation of efficient vaccines but are currently undefined. In this study, we used a mouse model of influenza to demonstrate that the absence of gamma interferon (IFN-γ) or IFN-γ receptor 1 (IFN-γR1) leads to aberrant contraction of antigen-specific CD8 T cell responses. The increased accumulation of the effector CD8 T cell population was independent of viral load. Reduced contraction was associated with an increased fraction of CD8 T cells expressing the interleukin-7 receptor (IL-7R) at the peak of the response, resulting in enhanced numbers of memory/memory precursor cells in IFN-γ−/− and IFN-γR−/− compared to wild-type (WT) mice. Blockade of IL-7 within the lungs of IFN-γ−/− mice restored the contraction of influenza virus-specific CD8 T cells, indicating that IL-7R is important for survival and is not simply a consequence of the lack of IFN-γ signaling. Finally, enhanced CD8 T cell recall responses and accelerated viral clearance were observed in the IFN-γ−/− and IFN-γR−/− mice after rechallenge with a heterologous strain of influenza virus, confirming that higher frequencies of memory precursors are formed in the absence of IFN-γ signaling. In summary, we have identified IFN-γ as an important regulator of localized viral immunity that promotes the contraction of antigen-specific CD8 T cells and inhibits memory precursor formation, thereby limiting the size of the memory cell population after an influenza virus infection.

Priming with high and low respiratory allergen dose induces differential CD4+ T helper type 2 cells and IgE/IgG1 antibody responses in mice

Sensitization of allergic patients normally takes place over several years and is the result of repeated exposure to low levels of allergen. Most mouse asthma models use a high dose of allergen administered over a short period. We have investigated the role of dose in the immune response to an inhaled respiratory allergen (Blomia tropicalis). We observed the effect of priming dose on the allergic response in mice intranasally immunized with low (0·5 μg) and high (50 μg) doses of B. tropicalis extract and killed 1 day after the last challenge. For both doses of allergen, T helper type 2 (Th2) cells and Th2 cytokines were evident as well as eosinophilic inflammation accompanied by mucus hyper‐secretion. By contrast, IgE and IgG1 antibody responses were normally only detected at high‐dose priming. To investigate the mechanism for these effects, we found group 2 innate lymphoid cells (ILC2s) were increased 48 hr after challenge in the low‐dose‐treated but not the high‐dose‐treated mice. Furthermore, we determined whether repeated low‐dose exposure with different priming protocols could induce an antibody response. Repeated low‐dose exposure to 0·5 μg three times weekly for 4 weeks (cumulative 6 μg) had the same effect as a shorter high‐dose exposure (cumulative 80 μg) and increasing cumulative dose induced antibody responses. These data indicate that low doses of allergen are sufficient to prime Th2 cells and ILC2s, but insufficient to induce antibody responses. Cumulative exposure to small amounts of allergen induces both Th2 and antibody responses and may better reflect natural sensitization.

Blomia tropicalis allergen 5 (Blo t 5) T-cell epitopes and their ability to suppress the allergic immune response

Blomia tropicalis is the major asthma allergen in the tropics comparable to Dermatophagoides pteronyssinus. However, little is known about the B. tropicalis epitopes recognized by T cells. Our aim was to identify the T‐cell epitopes in the major B. tropicalis allergen, Blo t 5, and investigate the potential of the corresponding peptides to inhibit the allergic inflammatory lung response. C57BL/6 mice were immunized with plasmid DNA encoding Blo t 5 and T‐cell epitopes identified using the interferon‐γ ELISPOT assay with 15‐mer overlapping peptides. C57BL/6 mice were sensitized with bone‐marrow‐derived dendritic cells (BMDC) pulsed with Blo t 5 allergen followed by intranasal Blo t 5 challenge. Two H‐2b restricted epitopes (Bt576–90 and Bt5106–115) were recognized by CD4 T cells specific for Blo t 5, but no CD8 epitopes were identified. In mice sensitized with Blo t 5‐pulsed BMDC and challenged with intranasal Blo t 5 Bt576–90 and Bt5106–115, peptide‐specific CD4 T cells were found to secrete the T helper type 2 cytokines interleukin‐5 and interleukin‐13. Intradermal administration of synthetic peptides encoding the identified T‐cell epitopes suppressed allergic airway inflammation to further allergen challenges. Hence, we have identified novel CD4 T‐cell epitopes specific for Blo t 5 and demonstrated that these peptides could be employed therapeutically to suppress the T‐cell response in a murine model of allergic airway inflammation.