Date of this Version
Gene maps of livestock are rapidly being developed and have led to an explosion of knowledge in recent years about genes affecting economic traits. One potential application of this information that would have major economic value is in selection of livestock for resistance to disease. Even though much has been learned about Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) since it was first identified, PRRSV continues to cause significant economic losses in many herds. Traditional approaches to manage PRRSV can be effective, but may be costly and have not always resulted in permanent control. This is a disease for which application of molecular genetic knowledge to select for resistance would have significant economic advantages. An experiment was initiated at Nebraska to investigate possible genetic variation among pigs in response to PRRSV. Pigs from two populations were infected with PRRSV, responses over 14 days were recorded, and tissues were collected at necropsy for gene expression studies. Phenotypic data, including body weights and rectal temperatures, viremia, and lung lesion scores, provided substantial evidence that genetic variation in response to PRRSV exists. With that knowledge, we developed an index of high (H) and low (L) responders, indicating susceptible and resistant phenotypes, and measured expression differences in lung and bronchial lymph node of 11 immune function genes between H and L pigs. Ten of these genes, involving both innate and acquired immune function, were expressed differently in lung and/or lymph tissue. They tended to be up-regulated (expressed at greater levels) in H pigs. We demonstrated that genetic variation in response to PRRSV exists and that both innate and acquired genes are involved. We have not yet determined whether selection for the immune function genes involved or levels of the proteins they produce will be effective in selecting for PRRSV resistance. Results will be helpful in additional investigations aimed at developing methods to select for resistance to PRRSV.