Volume 8 Issue 6, June 2008

It was thought that intestinal epithelial cells functioned solely as a barrier to the external environment, but as described here, these cells are now known to have an integral role in facilitating and controlling crosstalk between commensal bacteria and the immune system.

IgA is the most abundant antibody class and provides a first line of defence at mucosal surfaces. Class switching to IgA occurs through both T-cell-dependent and T-cell-independent pathways, and recent studies reveal a role for commensal bacteria in intestinal IgA responses.

A delicate balance between tolerance to commensal bacteria and immunity to pathogens occurs in the intestine. Intestinal dendritic cells have a central role in maintaining this balance and, as described here, some of the molecular pathways involved have recently been resolved.

Infection by HIV requires the virus to breach the mucosal barrier to gain access to the immune cells that it infects. But what are the immediate events that follow HIV exposure at genital mucosal sites and what are the key cells that facilitate HIV invasion?

Great progress has been made recently in the identification of genes or genetic loci that are associated with inflammatory bowel diseases. This knowledge is now providing insight into the pathogenesis of these diseases, highlighting roles for genes involved in bacterial sensing and cytokine signalling.

This Review describes how the expression of inhibitory members of the B7 family, particularly B7-H1 and B7-H4, by cancer cells, stromal cells and haematopoietic cells in the tumour microenvironment is regulated and acts to inhibit T-cell immunity, as well as the therapeutic implications.

In this Opinion article, Stephen Galli and colleagues discuss the recent evidence that mast cells can have negative, as well as positive, immunomodulatory functions, and suggest that mast cells might have distinct roles at different phases of an immune response.

Most infectious, allergic and inflammatory diseases in humans involve mucosal surfaces, including the gastrointestinal, reproductive and respiratory tracts. To maintain health, the mucosal immune system must provide protection against pathogens while being tolerant of commensal bacteria and harmless antigens. This Focus highlights the latest advances in our understanding of host-microbe interactions at mucosal sites and the consequences of immune dysregulation at these sites.