ANTI-HEMOLYSIN IGG1 TO IGG2 RATIOS CORRELATE WITH HEMOLYSIN NEUTRALIZATION TITERS AND LUNG LESION SCORES IN ACTINOBACILLUS-PLEUROPNEUMONIAEINFECTED-PIGS

Currently available porcine Actinobacillus pleuropneumoniae bacterins afford only minimal protection by decreasing mortality but not morbidi ty. To evaluate a possible role of IgG subclasses in protection, IgG1 and IgG2 responses to A. pleuropneumoniae haemolysin (HLY) were examin ed in piglets exposed to a low dose (10(5) c.f.u. ml(-1)) of A. pleuro pneumoniae CM5 (LD) given by aerosol (which affords complete protectio n) or bacterin-vaccinated piglets (no protection). Only the LD group d eveloped HLY neutralizing antibody. These animals produced both IgG1 a nd IgG2-associated antibody in response to HLY, and there was a positi ve correlation (r = 0.6) between IgG1 anti-HLY antibody and neutralizi ng titres, Anti-HLY IgG1 antibody was negatively correlated with pneum onic scores at necropsy (r = -0.67, p less than or equal to 0.005). Th ese results suggest that immunization procedures that bias anti-HLY an tibody to IgG1 may be more efficacious than chose inducing IgG2. (C) 1 998 Elsevier Science Ltd. All rights reserved.