SLOW-REACTING AND COMPLEMENT-REQUIRING NEUTRALIZING ANTIBODY IN SWINEINFECTED WITH PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME (PRRS) VIRUS

Various conditions were evaluated and modified to enhance the sensitiv ity of the neutralization (NT) test for detecting antibody in swine in fected with porcine reproductive and respiratory syndrome (PRRS) virus . Higher NT antibody titers were consistently obtained by the addition of 10% (v/v) complement, fresh guinea pig serum, to the virus diluent and by the incubation of serum-virus mixture at 4 degrees C for 24 hr . The appearance and persistence of antibodies detected by the modifie d NT test showed a similar pattern to those of antibodies detected by the indirect fluorescent antibody (IFA) assay, although the antibody t iters obtained by the former method were consistently lower than those obtained by the latter method. Slow-reacting complement-requiring NT antibody was detected in sera from pig 2 weeks after infection with PR RS virus. The slow-reacting complement-requiring NT antibody in the ea rly serum samples was sensitive to 2-mercaptoethanol (2-ME), whereas t he slow-reacting complement-requiring NT antibody in the late serum sa mples was resistant to 2-ME. The initial phase may represent the IgM r esponse and the later phase a change to IgG. A NT test was developed i n which serum-virus mixtures were incubated at 4 degrees C for 24 hr w ith complement; this gave an improved sensitivity over the previous in cubation at 37 degrees C for 60 min.