Rh. Yu et al., Analysis of the immunological responses to transferrin and lactoferrin receptor proteins from Moraxella catarrhalis, INFEC IMMUN, 67(8), 1999, pp. 3793-3799
Moraxella catarrhalis expresses surface receptor proteins that specifically
bind host transferrin (Tf) and lactoferrin (Lf) in the first step of the i
ron acquisition pathway. Acute- and convalescent-phase antisera from a seri
es of patients with M. catarrhalis pulmonary infections were tested against
Tf and Lf receptor proteins purified from the corresponding isolates. Afte
r the purified proteins had been separated by sodium dodecyl sulfate-polyac
rylamide gel electrophoresis and Western blotting, we observed strong react
ivity against Tf-binding protein B (TbpB; also called OMP1) and Lf-binding
protein B (LbpB) but little or no reactivity against Tf-binding protein A (
TbpA) or Lf-binding protein A (LbpA), using the convalescent-phase antisera
, Considerable antigenic heterogeneity was observed when TbpBs and LbpBs is
olated from different strains were tested with the convalescent-phase antis
era, Comparison to the reactivity against electroblotted total cellular pro
teins revealed that the immune response against LbpB and TbpB constitutes a
significant portion of the total detectable immune response to M. catarrha
lis proteins. Preparations of affinity-isolated TbpA and LbpA reacted with
convalescent-phase antisera in a solid-phase binding assay, but blocking wi
th soluble TbpB, soluble LbpB, or extracts from an LbpA(-) mutant demonstra
ted that this reactivity was attributed to contaminants in the TbpA and Lbp
A preparations. These studies demonstrate the immunogenicity of M. catarrha
lis TbpB and LbpB in humans and support their potential as vaccine candidat
es.