R binding to AM779. Serum from an adjuvant only immunized animal (D) was used as a negative control. Probing with anti-His antibody was used as a positive control for presence of each recombinant protein domain (C). The position and size of molecular weight order IQ-1 standards is indicated to the left of the images and the arrow designates the immunodominant Msp2. doi:10.1371/journal.pone.0046372.gnot stimulated by any of the A. marginale antigens (Table 2). In contrast to the T cell responses, there was no significant difference in IgG2 titers to AM779 between the outer membrane vaccinates and the AM779 vaccinates either two weeks following the last immunization or immediately pre-challenge. This indicates that for B cell responses, and specifically those leading to classswitching to the relevant opsonizing subclass IgG2 [6],[29], abundance within the complex immunogen is not a primary determinant of sub-dominance.Table 2. Cell 1326631 mediated responses following immunization with Anaplasma marginale complex immunogen or AM779.Animal NumberVaccineMHC II haplotypesaStimulation Indexb OM AM779 0.6 4.0 1.8 1.2 1.3 6.3 21.2 6.4 4.3 3.0 0.9 1.8 0.9 1.7 1.Clostridium4.2 4.8 13.7 13.3 8.9 11.3 127 34.3 13.5 24.6 11.7 3.9 19.6 12.3 2.082 100 108OM OM OM OM OM AM779 AM779 AM779 AM779 AM779 Adjuvant Adjuvant Adjuvant Adjuvant Adjuvant23/22 16/24 8/3 24/24 24/24 23/24 16/12 8/3 8/24 24/24 23/3/27 23/27 16/3 16/8 24/2.1 9.3 19.1 19.1 2.6c 1.7 13 1.7 2.4 0.9 0.4 1.1 1.2 1.3 1.Table 1. Comparison of titers to AM779 and Msp2 in Anaplasma marginale complex immunogen vaccinates.b MHC II haplotypesa IgG2 titer171 091 113Animal Number Vaccine137 149 099 109 123 146aAM779 953 966 975 978 982 933 946 952 961aMsp2 .30,000 .30,000 .30,000 .30,000 .30,000 .30,000 .30,000 .30,000 20,000 20,OMc OM OM OM OM CSPd16/24 22/24 16/16 24/24 16/8 22/24 24/24 16/24 15/24 16/100 100 100 100 1000 1000 1000 1000 ,100e ,100eCSP CSP CSP CSPDetermined by DRb3 BIBS39 alleles. Endpoint titers determined by immunoblotting. OM, outer membrane immunized animals. d CSP, cross-linked surface complex immunized animals. e Negative at the lowest dilution tested, 1:100. doi:10.1371/journal.pone.0046372.tb cDetermined by DRb3 alleles. Stimulation index (SI) calculated as the mean count per minute (cpm) of triplicate cultures with specific antigen divided by the cpm of triplicate cultures stimulated with the negative control protein Msa-1. Stimulation indices 2 were considered significant and are in bold. c Response was only detected when antigen was used at a final concentration of 3 mg/ml. doi:10.1371/journal.pone.0046372.tbSubdominant Bacterial AntigensInfectious challenge stimulates an anamnestic response to AMChallenge of outer membrane and AM779 vaccinates by feeding A. marginale infected ticks represents natural transmission in terms of bacterial structure in the inoculum, the route, and 
the infectious dose [27]. For animals in both groups of vaccinates, the titers to AM779 increased following challenge (Table 3). The increase was earlier in the AM779 groups in which all animals had significant increases in titer (p = 0.008, one-tailed Mann-Whitney U Test) by one week post-challenge while a similar increase was not observed in the outer membrane vaccinated group until the second week post-challenge.IgG2 titers to AM779 do not correlate with protectionImmunization with AM779 did not confer protection against bacteremia: all AM779 vaccinates became infected and had mean peak levels greater than 108 bacteri.R binding to AM779. Serum from an adjuvant only immunized animal (D) was used as a negative control. Probing with anti-His antibody was used as a positive control for presence of each recombinant protein domain (C). The position and size of molecular weight standards is indicated to the left of the images and the arrow designates the immunodominant Msp2. doi:10.1371/journal.pone.0046372.gnot stimulated by any of the A. marginale antigens (Table 2). In contrast to the T cell responses, there was no significant difference in IgG2 titers to AM779 between the outer membrane vaccinates and the AM779 vaccinates either two weeks following the last immunization or immediately pre-challenge. This indicates that for B cell responses, and specifically those leading to classswitching to the relevant opsonizing subclass IgG2 [6],[29], abundance within the complex immunogen is not a primary determinant of sub-dominance.Table 2. Cell 1326631 mediated responses following immunization with Anaplasma marginale complex immunogen or AM779.Animal NumberVaccineMHC II haplotypesaStimulation Indexb OM AM779 0.6 4.0 1.8 1.2 1.3 6.3 21.2 6.4 4.3 3.0 0.9 1.8 0.9 1.7 1.Clostridium4.2 4.8 13.7 13.3 8.9 11.3 127 34.3 13.5 24.6 11.7 3.9 19.6 12.3 2.082 100 108OM OM OM OM OM AM779 AM779 AM779 AM779 AM779 Adjuvant Adjuvant Adjuvant Adjuvant Adjuvant23/22 16/24 8/3 24/24 24/24 23/24 16/12 8/3 8/24 24/24 23/3/27 23/27 16/3 16/8 24/2.1 9.3 19.1 19.1 2.6c 1.7 13 1.7 2.4 0.9 0.4 1.1 1.2 1.3 1.Table 1. Comparison of titers to AM779 and Msp2 in Anaplasma marginale complex immunogen vaccinates.b MHC II haplotypesa IgG2 titer171 091 113Animal Number Vaccine137 149 099 109 123 146aAM779 953 966 975 978 982 933 946 952 961aMsp2 .30,000 .30,000 .30,000 .30,000 .30,000 .30,000 .30,000 .30,000 20,000 20,OMc OM OM OM OM CSPd16/24 22/24 16/16 24/24 16/8 22/24 24/24 16/24 15/24 16/100 100 100 100 1000 1000 1000 1000 ,100e ,100eCSP CSP CSP CSPDetermined by DRb3 alleles. Endpoint titers determined by immunoblotting. OM, outer membrane immunized animals. d CSP, cross-linked surface complex immunized animals. e Negative at the lowest dilution tested, 1:100. doi:10.1371/journal.pone.0046372.tb cDetermined by DRb3 alleles. Stimulation index (SI) calculated as the mean count per minute (cpm) of triplicate cultures with 
specific antigen divided by the cpm of triplicate cultures stimulated with the negative control protein Msa-1. Stimulation indices 2 were considered significant and are in bold. c Response was only detected when antigen was used at a final concentration of 3 mg/ml. doi:10.1371/journal.pone.0046372.tbSubdominant Bacterial AntigensInfectious challenge stimulates an anamnestic response to AMChallenge of outer membrane and AM779 vaccinates by feeding A. marginale infected ticks represents natural transmission in terms of bacterial structure in the inoculum, the route, and the infectious dose [27]. For animals in both groups of vaccinates, the titers to AM779 increased following challenge (Table 3). The increase was earlier in the AM779 groups in which all animals had significant increases in titer (p = 0.008, one-tailed Mann-Whitney U Test) by one week post-challenge while a similar increase was not observed in the outer membrane vaccinated group until the second week post-challenge.IgG2 titers to AM779 do not correlate with protectionImmunization with AM779 did not confer protection against bacteremia: all AM779 vaccinates became infected and had mean peak levels greater than 108 bacteri.