Brain levels of neuropeptide Y in experimental pneumococcal meningitis

Models of experimental bacterial meningitis. Role and limitations

The seriousness of bacterial meningitis has encouraged the development of animal models that characterize complex pathogenetic and pathophysiologic mechanisms, provide evaluation of pharmacokinetic and antimicrobial effects of antibiotics (especially since the worldwide emergence of multiresistant bacteria), and establish new adjuvant treatment strategies (e.g., use of anti-inflammatory agents). The information obtained from an animal model depends on the site of inoculation. For example, using intranasal, intravenous, subcutaneous, or intraperitoneal inoculation, it is the bacterial and host factors that determine the development of bacteremia and the potential for a pathogen to invade the central nervous system that primarily are studied. In contrast, experimental models using direct inoculation into the cerebrospinal fluid can reliably produce lethal infections over a predictable time course. Furthermore, because adult animals will not reliably develop meningitis after intranasal or intraperitoneal challenge, infant animals are used. Because these models bypass the natural dissemination of bacteria from the intravascular compartment to the central nervous system, the pathogenesis is artificial. These models, however, are extremely useful for the study of pathogen and host factors leading to meningeal inflammation and resulting complications, and for evaluating potentially useful agents for treatment therapy. During the past decade, the design of clinical studies has been stimulated by findings obtained from these animal models.

The pathophysiology of pneumococcal meningitis

The interactions between pneumococcal surface components and host defence systems that initiate pneumococcal meningitis have been studied in considerable molecular detail over the past decade. In this sense, the pneumococcus has served as a prototype for the unravelling of the genesis of inflammation caused by gram-positive bacteria. This review outlines the progression of these early events involving the cytokine cascade, the coagulation cascade, and leukocyte migration, and relates these processes to the production of blood-brain barrier permeability, the hallmark of injury in meningitis. This new understanding has radically altered the therapy of disease with the promise of greatly improved outcome.

Neuropeptide Y is an inducible gene in the human immune system

This study reports on neuropeptide Y (NPY) mRNA expression in human peripheral blood mononuclear cells (PBMC) and lymphoid tissues. By reverse transcription polymerase chain reaction (RT-PCR) it is shown that activated human PBMC of normal blood donors expressed the NPY gene. The PCR products had the expected size and Northern blotting demonstrated the presence of the 0.8-kb NPY mRNA. To define the subpopulations of mononuclear cells expressing this neuropeptide, purified monocytes, B cells and T cells were stimulated with specific activators. Monocytes and in vitro matured macrophages expressed NPY mRNA in response to phorbol myristate acetate (PMA). B lymphocytes expressed NPY mRNA following stimulation with antibody to surface immunoglobulin and PMA. In order to analyze whether these cell types express NPY under physiological conditions in vivo, human bone marrow, tonsil and thymus were analyzed. In situ hybridization of bone marrow revealed a small number of cells containing high levels of NPY mRNA which was also detected in RNA extracts of human thymus and tonsil. In summary, NPY is an inducible gene in human lymphocytes and monocytes and it is expressed at sites where these cells are activated in vivo.