Bactericidal action of a complement-independent antibody against relapsing fever Borrelia resides in its variable region.
A single chain variable fragment (scFv) of CB515, a complement-independent bactericidal monoclonal IgM against a relapsing fever Borrelia, was constructed to investigate the region wherein the unique bactericidal function resides. Monomeric CB515 scFv (26 kDa) was capable of binding its Ag on whole organisms and by immunoblot. This binding was shown to be species and serotype-specific to the 19 kDa variable small protein, recognized by its parent monoclonal IgM. A dose-dependent bactericidal effect of the CB515 scFv was detected by direct enumeration of spirochetes. Spirochetes incubated with the CB515 scFv before inoculation into mice grew into escape mutants, whereas spirochetes incubated with an irrelevant scFv developed as the original infecting serotype. This bactericidal effect, as seen at the ultrastructural level, was due to disruption of the outer membrane and to severe membrane blebbing eventually progressing to lysis. These results indicate that the variable region of CB515 is responsible for this bactericidal activity and that the constant region of the Ab is dispensable.
LaRocca
Timothy J
TJ
Center for Infectious Diseases, Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, NY 11794, USA.
Katona
Laura I
LI
Thanassi
David G
DG
Benach
Jorge L
JL
D000818:Animals; D000907:Antibodies, Bacterial / Q000737:chemistry / Q000276:immunology / Q000494:pharmacology*; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology / Q000494:pharmacology*; D001898:Borrelia / Q000276:immunology / Q000378:metabolism*; D003165:Complement System Proteins / Q000276:immunology; D004305:Dose-Response Relationship, Drug; D007075:Immunoglobulin M / Q000737:chemistry / Q000276:immunology / Q000494:pharmacology*; D007135:Immunoglobulin Variable Region / Q000737:chemistry / Q000276:immunology / Q000494:pharmacology*; D051379:Mice; D012061:Relapsing Fever / Q000276:immunology / Q000382:microbiology*
D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D007075:Immunoglobulin M; D007135:Immunoglobulin Variable Region; D003165:Complement System Proteins