Serum-virus titers after challenge for group E (Mock-vaccinated control), F (IFA adjuvant) and G (Alhydrogel adjuvant). Virus titers in serum (log₁₀ TCID₅₀/mL) were determined by virus titration on PAM, followed by immunoperoxidase staining for the PRRSV nucleocapsid protein.  = challenge. Symbols represent individual animals and lines represent mean virus titers in each group. The dashed line gives the mean titers for group E. The dotted line gives the detection limit for virus titration.