Table 1.

Amount of hyperimmune OspA antiserum required to protect mice from tick-borneB. burgdorferi infectiona

Antiserum and dilutionMean circulating C3.78 equivalents (μg/ml) in recipient mice (SD)No. infected/total (% infected)Mean no. of borreliae per tick (SD)b
MiceTicks
GST (undiluted)04/4 (100)13/13 (100)49,000 (23,900)
OspA
 Undilutedc 216.3 (45.3)0/4 (0)2/13 (15)15 (20)*
 1:548.5 (5.3)0/4 (0)9/12 (75)300 (600)*
 1:256.0 (1.8)0/4 (0)7/13 (54)7,900 (9,100)*
 1:504.5 (0.5)4/4 (100)12/12 (100)8,500 (4,100)*
 1:100<24/4 (100)12/15 (80)29,200 (21,800)
 1:200<24/4 (100)9/9 (100)26,300 (17,700)
  • a Groups of four mice were passively administered a control antiserum (GST) or different dilutions of hyperimmune OspA antiserum. The antisera were administered by injecting 200 μl (100 μl subcutaneously and 100 μl intraperitoneally) at the appropriate dilution in each mouse. Twenty-four hours after passive immunization, the mice were challenged by placement of 10 nymphal ticks infected with B. burgdorferi B31 on each mouse. At the time of challenge, the mice were bled and the circulating titer of passively administered antibody binding to the C3.78 protective epitope was determined. The ticks were allowed to feed to repletion and detach from the mice. The mice were tested for B. burgdorferi infection by culturing selected organs in BSK II medium as described in Materials and Methods. After the ticks detached, they were tested to determine the prevalence of infected ticks in each group as well as the mean number of spirochetes within individual ticks from each group.

  • b For the OspA antibody-treated groups, an asterisk indicates that the mean number of spirochetes is significantly different from that in the control group (Student’s t test, P < 0.05).

  • c The undiluted hyperimmune OspA antiserum had 6,800 μg of C3.78 antibody equivalents per ml.