Abstract
Porcine respiratory disease complex (PRDC) is a polymicrobial syndrome that results from a combination of infectious agents, such as environmental stressors, population size, management strategies, age, and genetics. PRDC results in reduced performance as well as increased mortality rates and production costs in the pig industry worldwide. This review focuses on the interactions of two enveloped RNA viruses—porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza virus (SwIV)—as major etiological agents that contribute to PRDC within the porcine cellular innate immunity during infection. The innate immune system of the porcine lung includes alveolar and parenchymal/interstitial macrophages, neutrophils (PMN), conventional dendritic cells (DC) and plasmacytoid DC, natural killer cells, and γδ T cells, thus the in vitro and in vivo interactions between those cells and PRRSV and SwIV are reviewed. Likewise, the few studies regarding PRRSV-SwIV co-infection are illustrated together with the different modulation mechanisms that are induced by the two viruses. Alterations in responses by natural killer (NK), PMN, or γδ T cells have not received much attention within the scientific community as their counterpart antigen-presenting cells and there are numerous gaps in the knowledge regarding the role of those cells in both infections. This review will help in paving the way for future directions in PRRSV and SwIV research and enhancing the understanding of the innate mechanisms that are involved during infection with these viruses.
Highlights
The term delineates a more general term describing a polymicrobial syndrome that results from a combination of infectious agents, environmental stressors, population size, management strategies, age, and genetics that causes reduced performance, together with increase mortality rates and production costs in the pig industry worldwide
The innate immune system is the first line of defense against any infection and, in particular, for porcine reproductive and respiratory syndrome virus (PRRSV), lung MΦ, and dendritic cells (DC) is critical in the prevention of viral invasion in the blood circulation and inducing protective adaptive immunity
It has been shown that this subset increases in the lung following infection with H1N1 virus [120], in particular, the levels of γδ T cells were significantly higher in BAL and lower in tonsils of infected pigs when compared with control
Summary
The term porcine respiratory disease complex (PRDC) was used in the past to describe the pneumonia of multiple etiologies that cause clinical disease with negative consequences on productive parameters during the finishing process. The respiratory disease complex is the consequence of impairment of the normal respiratory immune system due to pathogens that are able to harm these defenses and establish infection on their own. Those microorganisms are normally considered to be the primary etiological agents and. We will focus, in particular, on two enveloped RNA viruses, PRRSV and SwIV, as major etiological agents that contribute to PRDC and on the recent discoveries in porcine cellular innate immunity during PRRSV and/or SwIV infection
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