title: Comparative analysis of the mucosal adjuvanticity of the type II heat-labile enterotoxins LT-IIa and LT-IIb.
abstract: Cholera toxin (CT) and the heat-labile enterotoxin of Escherichia coli (LT-I) are members of the serogroup I heat-labile enterotoxins (HLT) and can serve as systemic and mucosal adjuvants. However, information is lacking with respect to the structurally related but antigenically distinct serogroup II HLT, LT-IIa and LT-IIb, which have different binding specificities for ganglioside receptors. The purpose of this study was to assess the effectiveness of LT-IIa and LT-IIb as mucosal adjuvants in comparison to the prototypical type I HLT, CT. BALB/c mice were immunized by the intranasal (i.n.) route with the surface protein adhesin AgI/II of Streptococcus mutans alone or supplemented with an adjuvant amount of CT, LT-IIa, or LT-IIb. Antigen-specific antibody responses in saliva, vaginal wash, and plasma were assayed by enzyme-linked immunosorbent assay. Mice given AgI/II with LT-IIa or LT-IIb by the i.n. route had significantly higher mucosal and systemic antibody responses than mice immunized with AgI/II alone. Anti-AgI/II immunoglobulin A (IgA) antibody activity in saliva and vaginal secretions of mice given AgI/II with LT-IIa or LT-IIb was statistically similar in magnitude to that seen in mice given AgI/II and CT. LT-IIb significantly enhanced the number of AgI/II-specific antibody-secreting cells in the draining superficial cervical lymph nodes compared to LT-IIa and CT. LT-IIb and CT induced significantly higher plasma anti-AgI/II IgG titers compared to LT-IIa. When LT-IIb was used as adjuvant, the proportion of plasma IgG2a relative to IgG1 anti-AgI/II antibody was elevated in contrast to the predominance of IgG1 antibodies promoted by AgI/II alone or when CT or LT-IIa was used. In vitro stimulation of AgI/II-specific cells from the superficial lymph nodes and spleen revealed that LT-IIa and LT-IIb induced secretion of interleukin-4 and significantly higher levels of gamma interferon compared to CT. These results demonstrate that the type II HLT LT-IIa and LT-IIb exhibit potent and distinct adjuvant properties for stimulating immune responses to a noncoupled protein immunogen after mucosal immunization.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA. michmart@uab.edu
authors.forename: M
authors.initials: M
authors.lastname: Martin
authors.forename: D J
authors.initials: DJ
authors.lastname: Metzger
authors.forename: S M
authors.initials: SM
authors.lastname: Michalek
authors.forename: T D
authors.initials: TD
authors.lastname: Connell
authors.forename: M W
authors.initials: MW
authors.lastname: Russell
mesh_terms: D018829:Adhesins, Bacterial / Q000008:administration & dosage / Q000276:immunology; D000276:Adjuvants, Immunologic / Q000008:administration & dosage / Q000494:pharmacology*; D000281:Administration, Intranasal; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D000921:Antibody-Producing Cells / Q000276:immunology; D001427:Bacterial Toxins / Q000008:administration & dosage / Q000145:classification / Q000494:pharmacology*; D002772:Cholera Toxin / Q000008:administration & dosage / Q000494:pharmacology; D016207:Cytokines / Q000096:biosynthesis; D004768:Enterotoxins / Q000008:administration & dosage / Q000145:classification / Q000494:pharmacology*; D004926:Escherichia coli / Q000276:immunology*; D029968:Escherichia coli Proteins; D005260:Female; D007111:Immunity, Cellular; D018928:Immunity, Mucosal; D007114:Immunization; D007070:Immunoglobulin A / Q000097:blood; D007074:Immunoglobulin G / Q000097:blood; D051379:Mice; D008807:Mice, Inbred BALB C; D013295:Streptococcus mutans / Q000276:immunology
chemical_list: D018829:Adhesins, Bacterial; D000276:Adjuvants, Immunologic; D000907:Antibodies, Bacterial; D001427:Bacterial Toxins; D016207:Cytokines; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D002772:Cholera Toxin; C027538:heat-labile enterotoxin, E coli