Crossing barriers: infections of the lung and the gut

Abstract

Although known as respiratory pathogens, severe acute respiratory syndrome (SARS) and its sister coronaviruses frequently cause enteric symptoms. In addition, other classically non-enteric viruses (such as HIV and influenza) may also have enteric effects that are crucial in their pathogeneses. These effects can be due to direct infection of the gut mucosa, but can also be because of decreased antibacterial defenses, increased mucosal permeability, bacterial translocation, and systemic leak of endotoxin.

Figure 1

Alternative mechanisms of mucosal viral–bacterial interactions. (a) In the normal gut, intestinal flora are kept from invasion by the intact mucosa, even in the follicle-associated epithelium that specializes in transportation of antigen into the Peyer's patch. (b) If the submucosal lymphoid tissue is damaged by infection (e.g., with HIV), the mucosa becomes permeable to bacteria and to bacterial products. Translocation of bacteria and bacterial products from the intestinal lumen cause systemic innate stimulation, leading to malaise and other systemic symptoms. (c) If a virus is tropic for the intestinal epithelial cells, it causes cell damage and loosens the normally impermeable barrier that keeps bacteria in the intestinal lumen. PowerPoint slide