TABLE 2.

Antiadhesive properties of serum pools harvested from mice subjected to different regimens on live CFA/I⁺ ETEC bacteria, as evaluated by the ability to inhibit CFA/I-mediated binding to human erythrocytes (IHA) and Caco-2 cells

Vaccination regimena	IHA resultb		Caco-2 cells with bound bacteria (%)c
	Serum	Fecal extract
Nonimmunized	—	—	92
pRECFA	—	—	90
HG3	1:4	1:4	88
pRE4 + HG3	1:4	1:4	87
pRECFA + HG3	1:512	1:16	4*

^aSerum pools were from mice subjected to the following immunization protocols: nonimmunized; pRECFA, mice immunized with two i.m. doses (100 μg/dose) of pRECFA (titer of 4,268); HG3, mice immunized with two p.o. doses of the HG3 strain (10¹⁰ CFU/dose) (titer of 305); pRE4 + HG3, mice immunized with two doses of pRE4 followed 2 weeks later by two booster doses with the HG3 strain (titer of 420); pRECFA + HG3, mice subjected to the primer-booster regimen, with a 2-week interval between the priming and boosting immunizations (diluted in PBS to a final titer of 4,500).

^bCFA/I-specific antiadhesive potencies were measured by IHA with human group A red blood cells and the ETEC 258909-3 strain. Results are maximal dilutions of serum or fecal extract samples that yielded visible inhibition of the hemagglutination reactions. —, no visible reaction.

^cThe inhibition of adhesion of the ETEC 258909-3 strain to in vitro-cultivated Caco-2 cell monolayers was also measured. The results are expressed as percentages of Caco-2 cells with at least one attached bacterium visible under an optical microscope. All serum pools were used at a final dilution of 1:3 in d-mannose-containing PBS. Data were based on the total number of cells counted in two independent determinations. *, statistically different value (P < 0.05) compared to results obtained with serum samples from other vaccinated mouse groups.