Antibody responses and protective immunity in rats receiving repeated inoculations of Strongyloides ratti.

The relationship between specific antibody responses and protective immunity against Strongyloides ratti was examined in rats receiving 10, 50, or 500 infective larvae (L3) at weekly intervals. No specific IgG response was detected in rats receiving 10-L3 inoculations for 7 wk. Fifty- and 500-L3 inoculations induced an IgG response by weeks 2 and 3, respectively, and a higher IgG response was induced in rats receiving the higher doses. All 3 inoculation doses induced high IgE responses, but the kinetics were different. IgE in the 10-L3 group continued to rise from weeks 4 to 7. In the 50- and 500-L3 groups, IgE was detected first at week 3 and increased until week 5. It then declined in the 500-L3 group and the titer at week 7 was significantly lower than that at week 5, whereas it remained the same in the 50-L3 group. The number of larvae recovered from the head 40 hr after a challenge inoculation (1,000 L3) significantly declined by weeks 7, 3, and 2 in rats receiving 10, 50-, and 500-L3 inoculations, respectively. Intestinal worm burdens increased for 7 wk in the 10-L3 group, 5 wk for the 50-L3 group, and 2 wk for the 500-L3 group. These findings indicate that repeated inoculations of low doses of L3 induce delayed and limited protective immunity to a heavy challenge and worm expulsion from the intestine. There was a temporal correlation between the levels of protection and serum IgG, whereas circulating IgE level did not seem to affect directly either the level of the resistance or expulsion of intestinal worms.

Purification and characterization of N-acetylneuraminate synthase from Escherichia coli K1-M12.

N-Acetylneuraminate (NeuAc) synthase, which catalyzes NeuAc synthesis by condensation of N-acetyl-D-mannosamine (ManNAc) and phosphoenolpyruvate (PEP), was purified from a cell extract of Escherichia coli K1-M12 to electrophoretically homogeneity by serial column chromatographies. The molecular weight of native enzyme was estimated to be 106,000 by gel filtration. After denaturation in sodium dodecyl sulfate, the molecular weight was reduced to 52,000, indicating the existence of 2 identical subunits. The optimum pH was 7.5 and the stable pH range was 7.0 to 10.0. The enzyme was thermostable up to 30 degrees C. No metal ion was required for the enzyme activity. SH-inhibitors such as p-chloromercuribenzoic acid and mercury chloride were potent inhibitors. The K(m) for ManNAc and PEP were 5.6 mM and 0.04 mM, respectively.