SHORT COMMUNICATION Expression of toll-like receptors and co-stimulatory molecules in lymphoid tissue during experimental infection of beef calves with bovine viral diarrhea virus of low and high virulence Roberto A. Palomares & Jacqueline Parrish & Amelia R. Woolums & Kenny V. Brock & David J. Hurley Received: 12 May 2014 /Accepted: 5 August 2014 /Published online: 23 August 2014 # Springer Science+Business Media Dordrecht 2014 Abstract The objective of this study was to compare the mRNA expression of Toll-like receptors (TLR3 and TLR7), and costimulatory molecules involved in activation of lym- phocytes and antigen presenting cells (CD80, CD86, CD28, and CD40L) after experimental infection of beef calves with low or high virulence noncytopathic (ncp) bovine viral diar- rhea virus (BVDV) strains. Thirty BVDV-naïve, beef calves were intranasally inoculated with low (LV; n=10, SD-1) or high (HV; n=10, 1373) virulence ncp BVDVor with BVDV- free cell culture medium (Control, n=10). Calves were eutha- nized on day 5 post-inoculation and tracheo-bronchial lymph node (TBLN) and spleen samples were collected for mRNA expression through quantitative-RT-PCR. Levels of mRNA for TLR3 and TLR7 were increased in spleen of HV group (P <0.05), but not in LV group, compared to the control group. Expression of CD86 mRNA was up-regulated in TBLN of both LV and HV groups (P <0.05). A significant up-regulation of CD80 mRNA was observed in TBLN for LV calves (P <0.05), but not for HV calves. In conclusion, exper- imental inoculation with high virulence BVDV-2 1373 stim- ulated the expression of TLR3, TLR7 and CD86 in spleen and TBLN on day 5 post infection. In contrast, experimental challenge with the low virulence BVDV-1 SD-1 uniquely resulted in up-regulation of both CD80 and CD86 in TBLN samples on day 5 post infection. The observed differential expression during acute infection with high or low virulence BVDV might reflect differences in immune activation by these strains, which could be associated with differences in genotype and/or virulence. Keywords Bovine viral diarrhea virus . Virulence . Acute infection . Toll-like receptors, Co-stimulatory molecules Introduction Most bovine viral diarrhea virus (BVDV) acute infections are subclinical; However, BVDV is considered to be a potentiator of secondary infections resulting in clinical illness known as bovine respiratory disease complex (Baker 1995). The in- creased susceptibility to secondary infections is a consequence of the ability of BVDV to cause generalized immunosuppres- sion (Kapil et al. 2005). Infections with some virulent BVDV- 2 strains may result in severe clinical disease and high mor- tality rates (Liebler-Tenorio et al. 2003b). Thus, the viral strain virulence and immune status of the animal are major factors determining the wide range of clinical presentations following BVDV acute infections (Ridpath et al. 2006 ). Immunosuppression caused by BVDV infection has been associated with lymphoid depletion (Liebler-Tenorio et al. 2002, 2003a, b), leukopenia (Brodersen and Kelling 1999; Gånheim et al. 2005), and impairment of leukocyte function during innate and acquired immune responses (reviewed by Chase et al. 2004; Chase 2013). Toll-like receptors (TLR) are a family of membrane pro- teins expressed by many different types of cells, such as monocytes, macrophages, neutrophils, and dendritic cells that recognize a diverse array of pathogen-associated molecular patterns (PAMP) and stimulate innate immune response against those pathogens (Mifsud et al. 2014). Some TLRs, including TLR3 and TLR7 play a role in innate recognition of R. A. Palomares (*) : J. Parrish : D. J. Hurley Department of Population Health, College of Veterinary Medicine, University of Georgia, 425 River Rd, Athens, GA 30602, USA e-mail: palomnr@uga.edu A. R. Woolums Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-2771, USA K. V. Brock Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL 36849, USA Vet Res Commun (2014) 38:329–335 DOI 10.1007/s11259-014-9613-2