TABLE 1.

Levels of IgG antibodies to UspA1 and UspA2 and bactericidal activities in normal human sera

Persona	Age	ELISA IgG titerb		BC titerc
		UspA1	UspA2
1	2 mo	17,127	6,268	500
	6 mo	4,273	1,363	50
	15 mo	798	250	<50
2	2 mo	12,078	12,244	500
	6 mo	1,357	878	50
	18 mo	14,041	14,488	200
3	2 mo	30,283	20,362	500
	6 mo	1,077	1,947	50
	18 mo	2,478	1,475	<50
4	2 mo	2,086	869	<50
	6 mo	530	802	50
	18 mo	9,767	8,591	200
5	2 mo	3,233	2,655	<50
	6 mo	2,246	360	50
	18 mo	26,693	43,703	500
6	1.5–3 yr	4,036	2,686	50
7	1.5–3 yr	2,037	1,251	50
8	1.5–3 yr	341	251	<50
9	1.5–3 yr	2,538	1,200	500
10	1.5–3 yr	1,078	1,370	500
11	1.5–3 yr	1,265	953	50
12	Adult	161,750	87,180	450
13	Adult	873,680	248,290	1,350
14	Adult	154,650	146,900	450
15	Adult	10,330	7,860	50
16	Adult	35,780	31,230	150
17	Adult	19,130	132,200	450

^aThree consecutive samples from persons 1 through 5 were collected at the stated ages. 

^bELISA endpoint titers to purified UspA1 or UspA2 from the O35E strain were determined as the highest dilution of serum giving an A₄₁₅ greater than three times the background. 

^cBactericidal (BC) titers assayed against the O35E strain. The children’s sera were tested at dilutions of 1:50, 1:100, and 1:500. The adults’ sera were tested at dilutions of 1:50, 1:150, 1:450, and 1:1,350. Bactericidal titer was determined as the highest dilution of serum resulting in the killing of 50% or more of the bacteria relative to that of the control. Bacteria incubated with test serum and heat-inactivated complement serum gave titers of <50.