Anti-bacteroides lipopolysaccharide IgG levels in healthy adults and sepsis patients

Members of the genus Bacteroides greatly outnumber enterobacteria in the human colon and therefore represent a vast potential pool of biologically active LPS. An enzyme-linked immunosorbent assay was developed to estimate the distribution of IgG levels to LPS from B. fragilis, B. vulgatus, B. thetaiotaomicron and to a mixture of rough LPS from three enterobacteria and Pseudomonas aeruginosa in sera from 641 adult blood donors. By inhibition ELISA some cross-reactivity was demonstrated between the different anti-bacteroides LPS IgG, but with very little between the anti-bacteroides LPS IgG and the anti-enterobacterial/Pseudomonas LPS IgG. Serum IgG was measured daily over 5-9 day periods in 12 sepsis patients (6 survivors, 6 non-survivors) and in a healthy individual. In all patients IgG levels fluctuated to a greater extent than levels in a healthy subject. Variations all followed similar overall trends and indicated that exposure to bacteroides LPS had occurred. In 5 out of 6 survivors, IgG levels were rising at the end of the period, while 4 of the 6 non-survivors showed falls, with an exception showing increasing levels to B. fragilis LPS. In 5 out of 6 non-survivors, IgG levels against B. fragilis LPS were substantially higher than those against the other LPSs. In this small sample some trends in antibody kinetics have been recognised which suggest bacteroides LPS may be significant in sepsis, and indicate that this study should be extended.