Differences in competitors' market influence due to market structure: Evidence from Japanese gambling market.

This study investigates how differences in the market structure between the Japanese horse racing and Keirin1 racing markets affects the influence exercised by high-turnover operators (major operators) in both markets on low-turnover operators (minor operators) in those markets.2 In the horse racing market structure, there are few competitors, and the difference in turnover3 between major and minor operators is large. In contrast, in the Keirin racing market structure, there are many competitors, and the difference in turnover between major and minor operators is small. Panel analysis results show that in horse racing, operators with low turnover are significantly affected by those with high turnover, while in Keirin racing, operators with low turnover are less affected by competitors with high turnover. The results not only indicate that firms are affected differently by competitors due to the market structure but also suggest that this has an impact on market segmentation policies and firms' marketing efforts.

Effect of ultrafine zinc oxide (ZnO) nanoparticles on induction of oral tolerance in mice.

Ultrafine nanoparticles of zinc oxide (ZnO) recently became available as a substitute for larger-size fine ZnO particles. However, the biological activity of ultrafine ZnO currently remains undefined. In the present study, we investigated the effect of ultrafine ZnO on oral tolerance that plays an important role in the prevention of food allergy. Oral tolerance was induced in mice by a single oral administration (i.e., gavage) of 25 mg of ovalbumin (OVA) 5 days prior to a subcutaneous immunization with OVA (Day 0). Varying doses of ultrafine (diameter: approximately 21 nm) as well as fine (diameter: < 5 microm) ZnO particles were given orally at the same time during the OVA gavage. The results indicated that a single oral administration of OVA was followed by significant decreases in serum anti-OVA IgG, IgG(1), IgG(2a), and IgE antibodies and in the proliferative responses to the antigen by these hosts' spleen cells. The decreases in these immune responses to OVA were associated with a marked suppression of secretion of interferon (IFN)gamma, interleukin (IL)-5, and IL-17 by these lymphoid cells. Treatment with either ultrafine or fine ZnO failed to affect the oral OVA-induced suppression of antigen-specific IgG, IgG(1), IgG(2a), and IgE production or lymphoid cell proliferation. The suppression induced by the oral OVA upon secretion of IFN gamma, IL-5, and IL-17 was also unaffected by either size of ZnO. These results indicate that ultrafine particles of ZnO do not appear to modulate the induction of oral tolerance in mice.

Adjuvant effect of zinc oxide on Th2 but not Th1 immune responses in mice.

BACKGROUND AND AIM: We investigated the effect of zinc oxide (ZnO) on Th1 and Th2 immune responses in mice. MATERIAL AND METHODS: Mice were intraperitoneally administered with ovalbumin (OVA) with or without varying doses of ZnO (day 0). On day 21, anti-OVA IgG, IgG2a, IgG1, and IgE antibodies in sera, OVA-specific proliferative responses of spleen cells, and production of Th1 cytokines including IFN-gamma as well as Th2 cytokines such as IL-4 and IL-5 were measured. RESULTS: The results showed that administration of OVA with ZnO was followed by greater increases in anti-OVA IgG and the antigen-specific splenocyte proliferation compared to that of OVA alone. The production of anti-OVA IgG1 and IgE and secretion of IL-4 and IL-5 were markedly enhanced by ZnO. The enhancing effect of ZnO on these Th2 responses was as strong as aluminium hydroxide (Alum) that was widely used as an adjuvant. In contrast, treatment with OVA plus ZnO failed to affect production of anti-OVA IgG2a as well as IFN-gamma. It was also observed that ZnO had a stimulating effect on the secretion of the proinflammatory cytokine IL-17 from a new lineage of effector Th cells. CONCLUSION: These results suggest that ZnO appears to have an adjuvant effect on the immune system, especially Th2 but not Th1 immune responses.

Role of the Nh (Non-hair) mutation in the development of dermatitis and hyperproduction of IgE in DS-Nh mice.

The DS-Nh (DS Non-hair) mouse is a spontaneous hairless mutant of the DS mouse. The inheritance mode of the Nh mutation is autosomal dominant, and the Nh locus is mapped to Chromosome 11. The roles of the Nh mutation in spontaneous dermatitis and IgE hyperproduction were studied using an Nh congenic strain with a genetic background from the BALB/c mouse. In contrast to DS-Nh (Nh/+) mice, BALB/c-Nh (Nh/+) mice under conventional conditions showed a marked increase in serum IgE, without the development of dermatitis. These results suggest that IgE hyperproduction is regulated by the Nh mutation, while other genetic factor(s) are also involved in the development of dermatitis.

Spontaneous development of dermatitis in DS-Nh mice under specific pathogen-free conditions.

Spontaneous development of dermatitis in DS-Nh mice under specific pathogen-free conditions was examined to verify the hypothesis [Exp. Anim. 46: 225-229, 1997] that Stapylococcus aureus (S. aureus) infection is causally associated with the dermatitis. Observation of the mice up to 28 weeks of age indicated that obvious dermatitis does occur under S. aureus-free conditions, though the incidence was low (six of 42 females and two of 90 males). Skin lesions in the absence of this bacterium showed histological changes very similar to those that can be observed under conventional conditions. In addition, hyperproduction of serum IgE was demonstrated in the dermatitis-positive mouse. These findings suggested that the dermatitis is triggered by IgE-mediated allergic reactions.