Evaluation of indirect enzyme-linked immunosorbent assays and IgG avidity assays using a protein A-peroxidase conjugate for serological distinction between Brucella abortus S19-vaccinated and -infected cows.
This study aimed to evaluate the use of protein A-peroxidase (horseradish peroxidase [HRPO]) in indirect enzyme-linked immunosorbent assays (iELISAs) and IgG avidity assays for serological distinction between Brucella abortus S19-vaccinated and -infected cows. Four groups were analyzed: GI, 41 nonvaccinated seropositive cows; GII, 79 S19-vaccinated heifers analyzed at 3 months postvaccination; GIII, 105 S19-vaccinated cows analyzed after 24 months of age; and GIV, 278 nonvaccinated seronegative cows. IgG levels and avidity to B. abortus smooth lipopolysaccharide (S-LPS) were determined using anti-bovine IgG-HRPO or protein A-HRPO conjugates. Similar levels of IgG anti-S-LPS were found with GI using both conjugates. Lower IgG levels were detected with GII, GIII, and GIV using protein A-HRPO. Both conjugates showed high performance in discriminating GI from GIII, with high sensitivity (Se; 97.6%) and specificity (Sp; 97.1%). Protein A-HRPO was better in distinguishing GI from GIV (Se, 97.6%; Sp, 94.6%) and GI from GII (Se, 80.5%; Sp, 94.9%). Protein A-HRPO excluded a higher number of positive samples with GII and GIV. IgG avidity showed that protein A-HRPO, but not anti-IgG-HRPO, was able to distinguish nonvaccinated from vaccinated cattle, showing a higher avidity index (AI) with GI than with GII, with 78% of serum samples in GII showing an AI of <50%. Therefore, the iELISA using B. abortus S-LPS antigen and protein A-HRPO conjugate for preferential detection of the IgG2 subclass was shown to be suitable for serological distinction between S19-vaccinated and -infected cows. Also, antibodies generated after vaccination showed lower avidity, suggesting a role for the IgG2 subclass as an antibody of higher-affinity maturation after infection, constituting an additional tool for differentiating vaccinated from infected cattle.
Laboratory of Immunoparasitology, Institute of Biomedical Sciences, Federal University of Uberlândia, 38400-902 Uberlândia, MG, Brazil
Ana C A M
AC
Pajuaba
Deise A O
DA
Silva
José R
JR
Mineo
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D000915:Antibody Affinity; D002004:Brucella Vaccine / Q000276:immunology*; D002003:Brucella abortus / Q000276:immunology; D002006:Brucellosis / Q000175:diagnosis / Q000276:immunology / Q000662:veterinary*; D002417:Cattle; D002418:Cattle Diseases / Q000175:diagnosis* / Q000276:immunology; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D006735:Horseradish Peroxidase; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology*; D012698:Serologic Tests; D013205:Staphylococcal Protein A
D000907:Antibodies, Bacterial; D002004:Brucella Vaccine; D007074:Immunoglobulin G; D013205:Staphylococcal Protein A; D006735:Horseradish Peroxidase