DETECTION OF ANTIBODIES TO SHIGELLA LIPOPOLYSACCHARIDE IN URINE AFTERNATURAL SHIGELLA INFECTION OR VACCINATION

The purpose of the present study was to explore the possibility of det ecting antibodies to Shigella sonnei lipopolysaccharide (LPS) in urine after infection or vaccination, Urinary immunoglobulin A (IgA) and Ig G antibodies and specific IgA secretory protein against S. sonnei LPS were measured by enzyme-linked immunosorbent assay (ELISA), after adju stment for urine concentration. A significant antibody level was defin ed as one above a cutoff value calculated from the geometric mean + 2 standard deviations of urinary anti-S. sonnei LPS levels in 43 healthy hepatitis B vaccinees (controls), Of 11 culture-proven cases of S. so nnei shigellosis, at convalescence 9 (82%) had significantly elevated levels of urinary antibodies to the homologous LPS. The S. sonnei conj ugate vaccine, composed of S. sonnei O-specific polysaccharide covalen tly bound to recombinant exoprotein A of Pseudomonas aeruginosa, elici ted a significant urine IgA or IgG anti-UPS response in 60% (6 of 10), 56% (9 of 16), 43% (16 of 37), and 14% (3 of 21) of the volunteers at 2 weeks, 6 weeks, 6 months, and 12 months after vaccination, respecti vely. The specificity of the urine antibody response to S. sonnei LPS was documented by the total lack of response in subjects who received parenteral Shigella flexneri Za-recombinant exoprotein A conjugate (69 urine samples) or meningococcal tetravalent control vaccines (4 urine samples), All the volunteers who lacked a significant response to S. sonnei LPS in serum also lacked such response in urine samples, Sevent y-four percent of the volunteers with a significant IgA or IgG anti-UP S response in serum at convalescence or 14 days after vaccination show ed a similar response in urine. The ratio of the titer of secretory pr otein bound to IgA anti-S. sonnei LPS in urine to that in serum was 30 3 times higher than the ratio of anti-S. sonnei LPS total IgA titer in urine to that in serum, indicating that the urine IgA is of secretory origin. These findings suggest the possible use of urinary Shigella L PS antibodies as markers of systemic and secretory immune responses af ter natural infection or vaccination, At this stage, because of its li mited sensitivity, the detection by ELISA of Shigella LPS antibodies i n urine cannot replace the same assay in serum as a definitive test in an individual with a negative result.