ANTIBODY-PRODUCTION AND BLASTOGENIC RESPONSE IN PIGS EXPERIMENTALLY INFECTED WITH PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS

Seven five-week-old piglets were infected intranasally with 10(5) TCID 50 of porcine reproductive and respiratory syndrome (PRRS) virus strai n IAF.exp91. All virus-exposed pigs developed fever, labored abdominal breathing, conjunctivitis, and lymph node enlargement within the firs t 96 h postexposure (PE), which continued to d 10 to 14 PE, Two pigs t hat were necropsied at d 7 and 10 PE had diffuse interstitial pneumoni tis, cardiopathy and lymphadenopathy, All 5 remaining pigs produced se rum IgM and IgG antibodies against PRRS virus by 7 or 14 days PE, as d emonstrated by indirect immunofluorescence, This corresponded with the capability of isolating the virus from serum d 7 to d 49 or d 63 PE, Low serum neutralizing antibody titers were detected in 3 of the virus -exposed pigs by 35 days PE, A transient episode of diminished prolife rative response of peripheral blood lymphocytes to mitogens phytohemag glutinin (PHA) and concanavalin A (Con A) was observed in the virus-ex posed pigs at d 3 PE, However, in vitro spontaneous uptake of [H-3]-th ymidine was significantly increased in lymphocyte cultures of the same pigs at d 7 or d 14 PE, These results suggest polyclonal activation o f peripheral blood lymphocytes.