Masato Tohyama

IL‐12 protects mice against pulmonary and disseminated infection caused by Cryptococcus neoformans

We examined the role of IL‐12 in host resistance to Cryptococcus neoformans using a murine model of pulmonary and disseminated infection. In this model, mice were infected intratracheally with viable yeast cells. Mice untreated with IL‐12 allowed an uncontrolled multiplication of yeast cells in the lung with infiltrations of few inflammatory cells, and a cryptococcal dissemination to the brain and meningitis by 3 weeks, resulting in death of all animals within 4–6 weeks. IL‐12, when administered from the day of tracheal infection for 7 days, induced a marked infiltration of inflammatory cells, consisting mostly of mononuclear cells, and significantly reduced the number of viable yeast cells in the lung. The treatment suppressed brain dissemination, as shown by a marked reduction of yeast cells in the brain and prevention of meningitis. These effects resulted in a significant increase in the survival rate of infected mice. In contrast, late administration of IL‐12 commencing on day 7 after instillation of yeast cells failed to protect the mice against infection with C. neoformans. In further experiments, early administration of IL‐12 markedly induced interferon‐gamma (IFN‐γ) mRNA in the lungs of infected mice, while no IFN‐γ mRNA was detected without this treatment. Our results indicate that IL‐12 is effective when administered in the early period of pulmonary cryptococcal infection.

Contribution of tumour necrosis factor-alpha (TNF-α) in host defence mechanism against Cryptococcus neoformans

We investigated the role of TNF‐α in the host defence mechanism against infection with a virulent strain of Cryptococcus neoformans. Administration of exogenous recombinant human TNF‐α significantly prolonged the survival time of mice infected by intratracheal instillation of the organism. Surprisingly, neutralizing MoAb to murine TNF‐α did not shorten their survival time, a finding inconsistent with previous results. To investigate the cause of this inconsistency, we examined the production of TNF‐α in the lungs of infected mice. During the course of cryptococcosis, there was little or no generation of TNF‐α mRNA in the lung. This might be partly due to a direct inhibitory action of the fungal microorganism on TNF‐α production by macrophages. In vitro production of TNF‐α by murine interferon‐gamma (IFN‐γ)‐ and lipopolysaccharide (LPS)‐stimulated macrophages was strongly inhibited by co‐culturing with the whole yeast cells. In contrast, administration of recombinant murine IL‐12 markedly induced TNF‐α production and the neutralizing anti‐TNF‐α MoAb strongly blocked IL‐12‐induced protection of mice against cryptococcal infection. These results indicate that endogenously synthesized TNF‐α has the potential to contribute to the elimination of C. neoformans and partly mediates the protective effect of IL‐12.

Enhancing effect of oxygen radical scavengers on murine macrophage anticryptococcal activity through production of nitric oxide

We examined the roles of reactive nitrogen intermediates (RNI) and reactive oxygen intermediates (ROI) in interferon‐gamma (IFN‐γ)‐induced cryptococcostatic activity of murine peritoneal macrophages using NG‐monomethyl‐L‐arginine (L‐NMMA), a competitive inhibitor of RNI synthesis, and superoxide dismutase (SOD) and catalase, oxygen radical scavengers. IFN‐γ‐activated macrophages produced nitric oxide (NO) in a dose‐dependent manner, as measured by increased nitrite concentration in the culture supernatant. IFN‐γ also enhanced the suppressive effect on cryptococcal growth in a similar dose‐dependent manner. The induction of killing activity and NO production by an optimal dose of IFN‐γ (100 U/ml) was virtually suppressed by 500 μM L‐NMMA. These results confirmed the importance of the RNI‐mediated effector mechanism in anticryptococcal activity of macrophages. SOD and catalase significantly enhanced the cryptococcostatic activity of macrophages induced by a suboptimal dose of IFN‐γ (20 U/ml). The augmenting effect of these reagents was mediated by NO, since they potentiated the production of NO by macrophages and their effects were totally blocked by L‐NMMA. Our results indicate that the IFN‐γ‐induced anticryptococcal activity of macrophages is dependent mostly on RNI, and suggest that the ROI system down‐regulates the effector mechanism for cryptococcostasis by suppressing the RNI system.

Hamman-Rich syndrome revisited: how to avoid misdiagnosis

Please cite this paper as: Fujita et al. (2012) Hamman‐Rich syndrome revisited: How to avoid misdiagnosis. Influenza and Other Respiratory Viruses. DOI: 10.1111/j.1750‐2659.2012.00353.x.