TABLE 4.

Serum LPS Abs elicited in mice by S. flexneri 2a O-specific polysaccharide (SF) bound to C. difficile recombinant toxin A repeating units (rARU) alone or succinylated (rARUsucc)^a

Immunogen	Geometric mean (25th to 75th percentile) by ELISA
	IgG for injection:		IgM for injection:
	Second	Third	Second	Third
SF-rARU	0.75 (0.40–1.43)	1.61 (1.13–3.38)	6.92 (4.85–12.2)	7.18 (2.74–18.2)
SF-rARUsucc	0.37 (0.03–1.63)	2.48 (1.35–5.14)	1.54 (0.18–54.5)	4.06 (1.74–8.77)

^aFive-week-old mice were injected s.c. with 2.5 μg of S. flexneri type 2a O-specific polysaccharide alone or as a conjugate at 2-week intervals. Mice (n = 10) were exsanguinated before and 7 days after the third injection, and their sera were assayed for IgG anti-LPS by ELISA. A hyperimmune serum pool, arbitrarily assigned a value of 100 EU, served as a reference (29). Polysaccharide alone did not elicit Abs (data not shown). Statistical significance: third-injection value versus second-injection value for IgG anti-SF-rARUsucc, P = 0.04.