lactoferrin and Meningococcal-Infections

Pathogenic bacteria from the families Neisseriaeceae and Moraxellaceae acquire iron from their host using surface receptors that have the ability to hijack iron from the iron-sequestering host proteins transferrin (Tf) and lactoferrin (Lf). The process of acquiring iron from Tf has been well-characterized, including the role of the surface lipoprotein transferrin-binding protein B (TbpB). In contrast, the only well-defined role for the homologue, LbpB, is in its protection against cationic antimicrobial peptides, which is mediated by regions present in some LbpBs that are highly enriched in glutamic or aspartic acid. In this study we compare the Tf-TbpB and the Lf-LbpB interactions and examine the protective effect of LbpB against extracts from human and transgenic mouse neutrophils to gains insights into the physiological roles of LbpB. The results indicate that in contrast to the Tf-TbpB interaction, Lf-LbpB interaction is sensitive to pH and varies between species. In addition, the results with transgenic mouse neutrophils raise the question of whether there is species specificity in the cleavage of Lf to generate cationic antimicrobial peptides or differences in the potency of peptides derived from mouse and human Lf.

Topics: Animals; Anti-Infective Agents; Bacterial Proteins; Carrier Proteins; Cells, Cultured; Humans; Lactoferrin; Meningococcal Infections; Mice; Mice, Transgenic; Neisseria meningitidis; Neutrophils; Transferrin; Transferrin-Binding Protein B

Neisserial Heparin Binding Antigen (NHBA) is a surface-exposed lipoprotein ubiquitously expressed by Neisseria meningitidis strains and an antigen of the Bexsero® vaccine. NHBA binds heparin through a conserved Arg-rich region that is the target of two proteases, the meningococcal NalP and human lactoferrin (hLf). In this work, in vitro studies showed that recombinant NHBA protein was able to bind epithelial cells and mutations of the Arg-rich tract abrogated this binding. All N-terminal and C-terminal fragments generated by NalP or hLf cleavage, regardless of the presence or absence of the Arg-rich region, did not bind to cells, indicating that a correct positioning of the Arg-rich region within the full length protein is crucial. Moreover, binding was abolished when cells were treated with heparinase III, suggesting that this interaction is mediated by heparan sulfate proteoglycans (HSPGs). N. meningitidis nhba knockout strains showed a significant reduction in adhesion to epithelial cells with respect to isogenic wild-type strains and adhesion of the wild-type strain was inhibited by anti-NHBA antibodies in a dose-dependent manner. Overall, the results demonstrate that NHBA contributes to meningococcal adhesion to epithelial cells through binding to HSPGs and suggest a possible role of anti-Bexsero® antibodies in the prevention of colonization.

Topics: Antibodies, Bacterial; Bacterial Adhesion; Bacterial Outer Membrane Proteins; Binding Sites; Carrier Proteins; Cell Line; Epithelial Cells; Gene Knockout Techniques; Heparan Sulfate Proteoglycans; Heparin; Humans; Lactoferrin; Membrane Transport Proteins; Meningococcal Infections; Mutation; Neisseria meningitidis; Recombinant Proteins; Serine Endopeptidases

GNA2132 is a Neisseria meningitidis antigen of unknown function, discovered by reverse vaccinology, which has been shown to induce bactericidal antibodies in animal models. Here we show that this antigen induces protective immunity in humans and it is recognized by sera of patients after meningococcal disease. The protein binds heparin in vitro through an Arg-rich region and this property correlates with increased survival of the unencapsulated bacterium in human serum. Furthermore, two proteases, the meningococcal NalP and human lactoferrin, cleave the protein upstream and downstream from the Arg-rich region, respectively. We conclude that GNA2132 is an important protective antigen of N. meningitidis and we propose to rename it, Neisserial Heparin Binding Antigen (NHBA).

Topics: Amino Acid Sequence; Antibodies, Bacterial; Antigens, Bacterial; Antimicrobial Cationic Peptides; Blood Proteins; Carrier Proteins; Humans; Lactoferrin; Meningococcal Infections; Meningococcal Vaccines; Neisseria meningitidis; Virulence Factors

Bacteria have developed several mechanisms for iron uptake during colonization of mammalian hosts, where the availability of free iron is limiting for growth. Neisseria meningitidis expresses under iron-limiting conditions a receptor complex consisting of the lactoferrin-binding proteins A (LbpA) and LbpB to acquire iron from lactoferrin, which is abundantly present on the mucosal surfaces of the human nasopharynx. LbpA is an integral outer membrane-embedded iron transporter, whereas LbpB is a cell surface-exposed lipoprotein. In this study, we demonstrate that LbpB is also released into the culture medium. We identified NalP, an autotransporter known to be involved in the processing of other autotransporters, as the protease responsible for LbpB release. This release of LbpB reduced the complement-mediated killing of the bacteria when incubated with an LbpB-specific bactericidal antiserum. Since antibodies directed against LbpB are found in convalescent-patient sera, the release of an immunogenic protein as LbpB may represent a novel means for N. meningitidis to escape the human immune response.

Topics: Antibodies, Bacterial; Bacterial Outer Membrane Proteins; Bacterial Proteins; Blotting, Western; Carrier Proteins; Electrophoresis, Polyacrylamide Gel; Humans; Immunoblotting; Lactoferrin; Mass Spectrometry; Membrane Transport Proteins; Meningococcal Infections; Neisseria meningitidis; Serine Endopeptidases

An effective vaccine for serogroup B meningococci has yet to be developed and attention has turned to subcapsular antigens of the meningococcus as possible vaccine candidates. Iron binding proteins are being studied, with most interest focused on the transferrin binding proteins (TbpA and TbpB) and the ferric binding protein (FbpA). This study describes the purification of lactoferrin binding protein A (LbpA) from two meningococcal strains and assesses the human isotype-specific serum antibody response to these proteins in patients with proven meningococcal disease due to a range of phenotypes. Overall, fewer than 50% of sera contained IgG that recognised LbpA isolated from either strain and this antibody response was not uniform between the two proteins. There was some evidence that the antibody response varied between meningococcal phenotypes. This study demonstrates that LbpA does not induce a highly cross-reactive antibody response, indicating that it is unlikely to be an effective vaccine antigen.

Topics: Antibodies, Bacterial; Bacterial Outer Membrane Proteins; Humans; Immunoglobulin Isotypes; Lactoferrin; Meningococcal Infections; Neisseria meningitidis; Receptors, Cell Surface

Serum lactoferrin concentrations were elevated in almost all children with meningococcal septicemia, in whom the disease had been clinically apparent for less than 18 hours, while the concentrations were normal or only moderately elevated in patients who had had the disease longer before being admitted. Concentrations of C-reactive protein (CRP) were markedly elevated, even with a time lapse of less than six hours, making this the most suitable parameter for the early diagnosis of severe meningococcal infection. Following an operative injury on children the lactoferrin concentrations changed very little. More than six hours after an operation, however, a marked increase in CRP-values was observed, possibly indicating differentiation of this response from that of bacterial infection. The concomitant study of serum alpha 1-antitrypsin, alpha 1-antichymotrypsin, orosomucoid and haptoglobin did not uncover results of great significance with regard to early changes.

Topics: Acute Disease; alpha 1-Antichymotrypsin; alpha 1-Antitrypsin; C-Reactive Protein; Chymotrypsin; Haptoglobins; Humans; Infant, Newborn; Lactoferrin; Lactoglobulins; Meningococcal Infections; Orosomucoid; Sepsis; Time Factors