TABLE 5.

Passive protection of infant rats challenged with group C N. meningitidis with adult sera

Subject no. and serumb	Dilution	Strain 4243 (OAc positive) (expt 1A)a			Strain 4335 (OAc negative) (expt 1B)a
		Antibody dose (μg/rat)c	No. of animals positive for bacteremia/total no. tested	CFU/ml (geometric mean [103])	Antibody dose (μg/rat)	No. of animals positive for bacteremia/total no. tested	CFU/ml (geometric mean [103])
54
Pre	1:2	0.01	5/5	>500	≤0.01	5/5	313
Post	1:2	0.04	5/5	>500	≤0.04	5/5	>500
55
Pre	1:5	0.002	6/6	>500	≤0.002	3/3	>500
Postd	1:20	0.2	0/6	<0.001	0.14	3/5	0.897
Post	1:100	0.04	0/6	<0.001	0.03	5/6	21
Post	1:500	0.008	3/6	0.49	0.006	5/6	67
60
Pre	1:5	0.02	6/6	>500	≤0.02	5/5	378
Post	1:28	0.2	0/7	<0.001	0.08	1/5	0.008
Post	1:140	0.04	1/7	0.004	0.02	5/6	3
Post	1:700	0.008	6/7	6.0	0.003	6/6	>500

^aExperiments 1A and 1B were done on separate days. Results of experiments 2A, 2B, 3A, and 3B are shown in Table 6.

^bPre, preimmunization; post, postimmunization.

^cThe same respective dilutions of sera from each subject were tested against both strains. The antibody dose per rat for strain 4243 was calculated from the total antibody concentration measured by the RABA divided by the dilution. The antibody dose per rat for the OAc-negative strain 4335 was adjusted to take into consideration the percentage of antibody inhibited by soluble OAc-negative polysaccharide (see Fig. 1 and Table 4, footnote c).

^dFor subject 55, serum from 1 month postimmunization (39.5 μg/ml) was used for the passive-protection experiment with strain 4243. For the passive protection experiment with strain 4335, the serum from 2 months postimmunization was used because of insufficient quantity of the sample from 1 month postimmunization. Because the 2-month sample had a slightly higher antibody concentration than the 1-month sample (48.8 μg/ml), the 2-month serum was diluted 1:26, 1:130, and 1:650 to achieve doses of 0.2, 0.04, and 0.008 μg of total anticapsular antibody/rat, respectively.