Sozialwissenschaften

Anders als in der Medizin werden die für Forschung und Praxis nötigen Daten im Bereich der Sozialwissenschaften in erster Linie über Fragebogen und nicht durch die Messung biologisch-medizinischer Parameter gewonnen. In der Gesundheitsförderung und der Prävention setzt man Fragebogen häufig dann ein, wenn man etwas über das Wissen, die Wahrnehmungen oder subjektiven Beurteilungen zu bestimmten Verhaltensweisen, Zuständen oder Bedürfnissen von Personen bzw. Personengruppen erfahren möchte. Solche systematischen Befragungen, die das Ziel haben, Daten zu einem bestimmten Thema zu erheben, nennt man auch Surveys. Kenntnisse in der Entwicklung und Anwendung von Fragebogen sind unentbehrlich, wenn es darum geht, Public-Health-Studien zu beurteilen oder gar selbst durchzuführen. In diesem Abschnitt beschäftigen wir uns zuerst mit der Formulierung von guten Fragen und möglichen Antworten. Anschließend betrachten wir unterschiedliche Methoden der Datenerhebung und diskutieren ihre Vor- und Nachteile. Dabei gehen wir auch kurz auf die Methodik der qualitativen Verfahren ein. Schweizerische Lernziele: CPH 8, CPH 20

Functional flexibility of intestinal IgA - broadening the fine line

Intestinal bacteria outnumber our own human cells in conditions of both health and disease. It has long been recognized that secretory antibody, particularly IgA, is produced in response to these microbes and hypothesized that this must play an important role in defining the relationship between a host and its intestinal microbes. However, the exact role of IgA and the mechanisms by which IgA can act are only beginning to be understood. In this review we attempt to unravel the complex interaction between so-called "natural," "primitive" (T-cell-independent), and "classical" IgA responses, the nature of the intestinal microbiota/intestinal pathogens and the highly flexible dynamic homeostasis of the mucosal immune system. Such an analysis reveals that low-affinity IgA is sufficient to protect the host from excess mucosal immune activation induced by harmless commensal microbes. However, affinity-maturation of "classical" IgA is essential to provide protection from more invasive commensal species such as segmented filamentous bacteria and from true pathogens such as Salmonellatyphimurium. Thus a correlation is revealed between "sophistication" of the IgA response and aggressiveness of the challenge. A second emerging theme is that more-invasive species take advantage of host inflammatory mechanisms to more successfully compete with the resident microbiota. In many cases, the function of IgA may be to limit such inflammatory responses, either directly by coagulating or inhibiting virulence of bacteria before they can interact with the host or by modulating immune signaling induced by host recognition. Therefore IgA appears to provide an added layer of robustness in the intestinal ecosystem, promoting "commensal-like" behavior of its residents.

The habitat, double life, citizenship, and forgetfulness of IgA

Immunoglobulin A (IgA) is the main secretory immunoglobulin of mucous membranes and is powerfully induced by the presence of commensal microbes in the intestine. B cells undergo class switch recombination to IgA in the mucosa-associated lymphoid tissues, particularly mesenteric lymph nodes (MLNs) and Peyer's patches, through both T-dependent and T-independent pathways. IgA B cells primed in the mucosa traffic from the intestinal lymphoid structures, initially through the lymphatics and then join the bloodstream, to home back to the intestinal mucosa as IgA-secreting plasma cells. Once induced, anti-bacterial IgA can be extremely long-lived but is replaced if there is induction of additional IgA specificities by other microbes. The mucosal immune system is anatomically separated from the systemic immune system by the MLNs, which act as a firewall to prevent penetration of live intestinal bacteria to systemic sites. Dendritic cells sample intestinal bacteria and induce B cells to switch to IgA. In contrast, intestinal macrophages are adept at killing extracellular bacteria and are able to clear bacteria that have crossed the mucus and epithelial barriers. There is both a continuum between innate and adaptive immune mechanisms and compartmentalization of the mucosal immune system from systemic immunity that function to preserve host microbial mutualism.