Complex effect of adenovirus early region proteins on innate immune system

Adenoviruses (Ads) cause acute and persistent infections. The genome of Ads has five early transcription units that are the first viral genes expressed during an active infection. The Early Region 1A (E1A) gene of the adenovirus genome is crucial for adenovirus transformation of the host cell. Ads E1A block some aspects of the innate immune system to enable viruses to invade the host cell. E1A suppresses nitric oxide (NO) production through transcriptional control of the inducible NO synthase (iNOS) gene. This inhibition of NO production may enable the virus to persist in human tissue because NO is an antiviral effector of the innate immune system. E1A also blocks secretory leukoprotease inhibitor (SLPI) and elafin/skin-derived antileukoproteinase (SKALP) secretion by alveolar epithelial cells. Recent scientific evidence suggests that SLPI and elafin/SKALP have broad-spectrum antibiotic activities that include bactericidal and antifungal properties. The inhibition of inflammation by Ad early region proteins is complex, as certain early region proteins can promote as well as inhibit inflammation depending on the genetic context of the virus. E1A DNA and protein are frequently detected in the lungs of chronic obstructive pulmonary disease (COPD) patients and it is associated with an increased inflammatory response. E1A enhances intercellular adhesion molecule-1 and interleukin-8 mRNA expression with lipopolysaccharide stimulation. Understanding the roles of the Ad gene products in the induction and inhibition of innate inflammatory functions will help us to clarify the pathogenesis of the chronic respiratory illness including COPD.