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Related Concept Videos

Complement System01:27

Complement System

The complement system is a group of approximately 20 plasma proteins that strengthen the body's defenses against infections through opsonization, inflammation, and cell lysis. Opsonization involves coating pathogens with complement proteins, making them more recognizable and facilitating phagocyte engulfment. Certain complement proteins induce inflammation that attracts immune cells to the site of infection. Cell lysis involves the destruction of pathogens through the formation of a membrane...
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Influenza is an acute, highly communicable viral disease that affects the respiratory tract and is responsible for seasonal epidemics worldwide. Influenza A is the most prevalent type associated with widespread outbreaks and is subtyped based on two surface glycoproteins: hemagglutinin (H) and neuraminidase (N), as in H1N1. These glycoproteins are essential for viral infectivity, transmission, and immune recognition. Transmission occurs primarily through respiratory droplets and contaminated...
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Viral replication and dissemination rely on efficient mechanisms for host cell entry, genome replication, assembly, and release. Influenza viruses, such as types A and B, are negative-sense single-stranded RNA viruses with a segmented genome, that depend on two critical surface glycoproteins to carry out these processes: hemagglutinin (HA) and neuraminidase (NA). HA initiates infection by binding to sialic acid residues on the surface of host epithelial cells, facilitating receptor-mediated...
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Antimicrobial Proteins01:23

Antimicrobial Proteins

Antimicrobial proteins are important components of the immune system. They aid the body in combating pathogens by either killing them directly or hindering their replication processes. Four main types of antimicrobial substances are interferons, the complement system, iron-binding proteins, and antimicrobial proteins.
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Interferons (IFNs) are proteins produced by lymphocytes, macrophages, and fibroblasts infected with viruses. While IFNs cannot prevent viruses from entering and...
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Type II hypersensitivity involves IgG and IgM antibodies targeting cell surface antigens, leading to cell destruction. This can occur through complement activation, antibody-dependent cell-mediated cytotoxicity (ADCC), or acting as opsonins for phagocytosis. When excessive, these reactions cause significant tissue damage.Drug-induced hemolytic anemia is a common example, where drugs like penicillin or cephalosporins bind to red blood cells, forming drug-protein complexes. These complexes...

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Assays for Studying the Role of Vitronectin in Bacterial Adhesion and Serum Resistance
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Haemophilus influenzae interacts with the human complement inhibitor factor H.

Teresia Hallström1, Peter F Zipfel, Anna M Blom

  • 1Medical Microbiology, Department of Laboratory Medicine, Lund University, Malmö University Hospital, Sweden.

Journal of Immunology (Baltimore, Md. : 1950)
|June 21, 2008
PubMed
Summary

Haemophilus influenzae evades the immune system by binding complement inhibitors factor H (FH) and factor H-like protein 1 (FHL-1). This interaction protects bacteria from complement-mediated killing, enhancing survival.

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Area of Science:

  • Immunology
  • Microbiology
  • Complement System

Background:

  • Pathogenic microbes employ strategies to evade the host innate immune system.
  • The complement system is a crucial part of innate immunity, and its dysregulation can lead to disease.
  • Factor H (FH) and Factor H-like protein 1 (FHL-1) are key regulators of the alternative complement pathway.

Purpose of the Study:

  • To investigate the interaction between Haemophilus influenzae (Hib) and complement inhibitors FH and FHL-1.
  • To identify the specific binding domains of FH and FHL-1 on Hib.
  • To determine the functional consequences of this interaction on bacterial survival.

Main Methods:

  • Screening of clinical Haemophilus influenzae isolates for FH binding.
  • Detailed analysis of a high FH-binding isolate (Hib 541) using serum survival assays.
  • Identification of FH and FHL-1 binding domains using biochemical methods and Far Western blot.

Main Results:

  • The majority of clinical Haemophilus influenzae isolates bound FH.
  • Hib isolates with higher FH binding exhibited increased survival in normal human serum.
  • FH and FHL-1 bind to distinct domains on Hib, retaining cofactor activity and protecting bacteria from complement-mediated killing.

Conclusions:

  • Haemophilus influenzae actively interferes with the alternative complement pathway by binding FH and FHL-1.
  • This binding reduces complement-mediated bactericidal activity, leading to enhanced bacterial survival.
  • FH plays a protective role at the bacterial surface, highlighting a novel host-pathogen interaction.