ANTI-GAL BINDS TO PILI OF NEISSERIA-MENINGITIDIS - THE IMMUNOGLOBULIN-A ISOTYPE BLOCKS COMPLEMENT-MEDIATED KILLING

alpha 1,3-Galactosyl antibodies (anti-Gal) are ubiquitous natural huma n serum and secretory polyclonal antibodies that bind to terminal gala ctose-alpha 1,3-galactose (alpha-galactosyl) residues, Serum immunoglo bulin C (IgG) anti-Gal can block alternative complement pathway-mediat ed lysis of representative gram negative enteric bacteria that bind it to lipopolysaccharide or-galactosyl structures, thereby promoting sur vival of such bacteria in the nonimmune host, We wanted to know whethe r anti-Gal also could bind to the lipooligosaccharides (LOS) of Neisse ria meningitidis, To our surprise, we found that serum and secretory a nti-Gal bound to pili hut not to LOS of certain strains, This suggeste d the presence of an immunogenic pilus carbohydrate epitope, Mild peri odate oxidation of sodium dodecyl sulfate-polyacrylamide gel electroph oresis-separated outer membrane preparations from strains that bound a nti-Gal followed by labeling of the neoaldehyde groups resulted in the labeling of bands that corresponded to pilin and LOS, confirming that pilin contains carbohydrate structures, A Bandeiraea simplicifolia le ctin that also binds terminal alpha 1,3-galactosyl residues also bound to pilin, Serum IgG, IgA, and IgM anti-Gal as well as colostral secre tory IgA anti-Gal bound to pilin, as judged by immunoblotting, and to the pili of intact piliated organisms, as judged by immunoelectron mic roscopy. Total serum anti-Gal (IgG, IgA, and IgM) and purified serum I gA1 anti-Gal, but not its purified IgG isotype. blocked complement-med iated lysis of a piliated meningococcal strain that bound anti-Gal to its pili, Colostral anti-Gal secretory IgA blocked killing of the same strain, Thus, anti-Gal IgA may promote disease when it binds to the p ili of N. meningitidis strains.