TABLE 2.

Ability of C3.78 to prevent transmission of tick-borne B. burgdorferi in the absence of host complement^a

Passive immunization	Wild-type mice			Complement-deficient mice
	No. of infected ticks/total	Relative bacterial load (no. of bacteria per tick) ± SE (n = 8)	No. of infected mice/total	No. of infected ticks/total	Relative bacterial load (no. of bacteria per tick) ± SE (n = 6)	No. infected mice total
PBS	8/8	95 ± 52	4/4	8/8	71 ± 38	4/4
C3.78 (62.5 μg)	8/8	126 ± 24	0/4	6/6	72 ± 37	0/4

^aGroups of four normal or complement-deficient mice were immunized with either PBS or C3.78 (62.5 μg) and challenged with four infected I. scapularis nymphs per mouse. From each mouse, two of the nymphs were removed at 60 h and tested for spirochetes, and the remaining nymphs were allowed to feed to repletion. The results in this table are from one of two independent experiments. Ticks were assessed for infection by indirect immunofluorescence microscopy after 60 h of feeding. The bacterial load in each tick was estimated by counting the number of spirochetes in five microscope fields viewed with the 40× objective. The mean number of spirochetes per infected tick was not significantly different between C3.78 antibody-treated and contol groups or between normal and C3-deficient mice (Student's t test, P > 0.05; n = 6 to 8). Mice were assessed for infection by Western blot 3 weeks after tick feeding.