Western blot analysis of neisserial lipooligosaccharide at the lower femtomole level with normal human sera.

Lipooligosaccharide (LOS) is a major immunogenic component of pathogenic Neisseria species such as Neisseria meningitidis and N. gonorrhoeae. Recent immunochemical studies have found that normal human sera (NHS) contain bactericidal anti-LOS antibodies that bind to the oligosaccharide (OS) moiety of neisserial LOS. Although affinity-purified anti-LOS antibodies can be characterized using 10-100 ng of LOS samples (up to a few tens of pmoles), a more sensitive immunoblotting assay must be established in order to analyze NHS directly and characterize anti-LOS antibodies without affinity purification. We examined analytical PAGE/blot conditions using a 15-well mini gel. For the first time, Western blot detection of LOS at the lower femtomole level was accomplished by both chromogenic and chemiluminescent detection. A model LOS, 15253 LOS, was detected in a low femtomole range (62.5-500 pg, 16-125 femtomole) even with 10 pM of a monoclonal antibody (MAb) 2C7. Furthermore, detection of similar amounts (50-250 femtomole) of neisserial LOSs and Salmonella truncated lipopolysaccharides (LPSs) was also possible with 1:50 and with 1:100 diluted NHS. The results obtained here indicate that the binding of IgG in NHS to the LOS and LPS samples is probably due to their carbohydrate moieties. The detection level accomplished in this study should help not only to further characterize anti-LOS antibodies in blood and body fluids but also to analyze carbohydrate structures that are recognized by them.