IFN-γ mRNA expression is lower in Holstein cows infected with bovine leukemia virus with high proviral load and persistent lymphocytosis.

Bovine leukemia virus (BLV) is a retrovirus that affects primarily milky cows. Animals serologically positive to BLV show a Th1 cytokine profile with a predominance of interferon gamma (IFN-γ). IFN-γ has antiviral activity through mechanisms such as resistance to infection, inhibition of viral replication and apoptosis. The objective of this work was to determine the transcription levels of IFN-γ and its relationship with proviral load and persistent lymphocytosis in a population of Holstein cows of the province of Antioquia, Colombia. IFN-γ transcription levels were evaluated by qPCR in 140 Holstein cows. A one-way analysis of variance and a Student's t test were used to evaluate the differences between the means. The amount of IFN-γ mRNA found in BLV-positive cows was lower than in BLV-negative cows. Moreover, in the group of infected cows a lower level of IFN-γ mRNA expression was found in BLV and persistent lymphocytosis cows (BLV+PL) compared with BLV and aleukemia cows (BLV+AL). The level of IFN-γ mRNA expression was lower in cows with high proviral load (HPL) compared to cows with low proviral load (LPL). BLV infection is related to abnormal expression of IFN-γ mRNA, although IFN-γ has antiviral activity, its expression is affected by high proviral load. Keywords: cytokine; immune system; leukemia; bovine leukemia virus.

El componente racial influencia la resistencia a la infección con el virus de la leucosis bovina / The racial component influences resistance to infection with the bovine leukemia virus

RESUMEN El virus de la leucosis bovina (VLB) es un retrovirus que afecta principalmente el ganado lechero, reduciendo la producción de leche entre el 2,5 y 5%. La raza criolla colombiana Blanco Orejinegro (BON) es una raza rustica, bien adaptada, que ha mostrado resistencia in vitro a las infecciones ocasionadas por los virus de la fiebre aftosa y la estomatitis vesicular, así como las originadas por la bacteria Brucella abortus. El objetivo del presente estudio fue determinar si la raza BON y su cruce con Holstein son resistentes a la infección por el VLB. Se tomaron 124 muestras de sangre (59 Holstein, 40 BON y 25 BON x HOL) del mismo hato, se extrajo el DNA y se realizó una PCR-anidada correspondiente a una región del gen env de VLB. Se obtuvo un fragmento de 444 pb en los animales positivos. La prevalencia molecular del hato fue 33% para VLB. Se encontró diferencia significativa para infección por VLB entre los tres grupos raciales (p < 0,05). El porcentaje de infección fue del 55,9% para la raza Holstien, 5% para las vacas BON y 24% para el cruce BON x HOL; este último presentó una reducción en el porcentaje de infección del 32% respecto a la raza Holstein, lo cual puede ser atribuido a la presencia de genes de resistencia en la raza BON. Se comprobó que el nivel de infección es menor en vacas lecheras del cruce BON x HOL que en la raza lechera Holstein.

ABSTRACT The bovine leukemia virus (BLV) is a retrovirus that primarily affects dairy cattle, reducing milk production between 2.5 and 5%. The Colombian Blanco Orejinegro (BON) is a well-adapted, rustic, creole breed resistant to in vitro infections of Foot-and-mouth disease virus and vesicular stomatitis virus, as well as to Brucella abortus. This study aimed to determine if the crossing of BON and Holstein breeds is resistant to infection by BLV. Blood samples of 124 individuals (59 Holstein, 40 BON, and 25 BON x HOL) of the same herd were taken. The DNA was extracted, and a nested PCR was performed related to a region of the env gene of BLV. A fragment of 444 bp was obtained for positives animals. The molecular in-herd prevalence was 33% for BLV. A significant difference for BLV infection was found among the groups (p<0.05). The infection rate for the Holstein group was 55.9%, for BON cattle 5%, and for BON x HOL cattle 24%. The latter showed a reduction in the infection rate of 32% to the Holstein breed, which can be attributed to the presence of resistance genes in the BON breed. It was found that the level of infection is lower in BON x HOL cattle in contrast with Holstein dairy cows.