Molecular mimicry

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Molecular mimicry describes the observation in pathogens that their proteins and carbohydrates in the course of an immune evasion partially adapt in their structures to those of their host . These partially aligned molecules are therefore less recognized by the immune system because similar or identical substances also occur in the host. Since the host organism does not normally form antibodies against its own molecules , these components of the pathogen are not recognized as antigen .

principle

In the reproduction of pathogens, mutants arise in rare cases , the acquisition of resources or the survival of a defense reaction of the host is easier (positive mutations), but mutations with negative effects usually arise. First and foremost, in order for a pathogen to survive, its functionalities (e.g. replication , infectivity ) must be ensured; as parasitic organisms and molecules , it also helps to avoid host resistance and an immune response . This applies in particular to pathogens with an Infect and persist course of infection which spend long periods of time in a host. The immune system recognizes proteins, carbohydrates and other larger molecules as antigens when they are foreign to its own body. H. usually not appear in it. In contrast, there is an immunological self-tolerance to the body's own molecules . Mutants of pathogens whose molecules trigger the host's own immune response less are less eliminated, which acts as a selection advantage. By imitating the host's own molecules, the defense reactions are reduced and, as with mimicry , the chances of survival are improved.

Examples (bacteria, viruses, protozoa, parasites)

In bekapselten bacteria to molecular mimicry could find. For example in the case of Streptococcus pyogenes . In the capsule of this group A streptococci is hyaluronic acid , a substance in the human connective tissue occurs. Some coli and Neisseria meningitidis sv. B carry sialic acid in their capsule, which is also part of gangliosides of the nervous system . Sialic acid was also found in Campylobacter jejuni . Helicobacter pylori expresses molecules that resemble the structure of CD15 .

In viruses, for example, the herpes simplex virus1 produces substances that are part of the cornea of the eye. The human herpesvirus 8 induces immune mediators such as MIP , interleukin-6 and IRF . Protozoa such as Trypanosoma cruzi produce proteins with cross-reactivity to human myosin . Parasites such as Schistosoma mansoni and Fasciola hepatica express CD15 and CD77, respectively .

Molecular Mimicry and Autoimmune Diseases

T cells and antibody producing B cells are checked for self-compatibility as they mature. When they recognize the body's own substances, they are usually eliminated in the thymus or bone marrow . However, if self-reactive auto-antibodies , B- and T-cells survive this selection, they can bind to mimicry molecules. As a result, an immune reaction occurs in which numerous antibodies are secreted that are directed against this (mimicry) antigen . However, the antibodies then also bind to the body's own molecules, which can kill host cells. In this way autoimmune diseases can develop. The Chagas disease , caused by Trypanosoma cruzi is an example. Life-threatening inflammation of the heart muscle ( myocarditis ) occurs due to the immune reaction against the host's own myosin. Infections with streptococci can Arthus reactions lead. Relationships between molecular mimicry and autoimmune diseases are widely discussed.

literature

  • C. Janeway et al .: Immunobiology . 6th edition ISBN 0-8153-4101-6 . The 5th English edition is available online on the pages of the NCBI Bookshelf (online) .
  • C. Delevoye et al .: SNARE protein mimicry by an intracellular bacterium . PLoS Pathog . (2008) 4 (3): e1000022 PMID 18369472
  • KY Hwa et al .: Peptide mimicrying between SARS coronavirus spike protein and human proteins reacts with SARS patient serum . J. Biomed. Biotechnol. (2008) PMID 18320019
  • Nir Drayman et al .: Pathogens Use Structural Mimicry of Native Host Ligands as a Mechanism for Host Receptor Engagement. In: Cell Host & Microbe. Volume 14, No. 1, 2013, pp. 63-73, doi: 10.1016 / j.chom.2013.05.005
  • Michael BA Oldstone (Ed.): Molecular Mimicry. Infection Inducing Autoimmune Disease. Springer, Berlin 2005, ISBN 3-540-25597-4 ( Current Topics in Microbiology and Immunology. 296).

Individual evidence

  1. ↑ Zhao ZS et al .: Molecular mimicry by herpes simplex virus-type 1: autoimmune disease after viral infection . In: Science . (1998) 279 (5355): pp. 1344-1347 PMID 9478893
  2. ↑ PS Moore et al .: Molecular mimicry of human cytokine and cytokine response pathway genes by KSHV . In: Science (1996) 274 (5293): pp. 1739-1744 PMID 8939871
  3. ↑ LK Iwai et al .: T-cell molecular mimicry in Chagas disease: identification and partial structural analysis of multiple cross-reactive epitopes between Trypanosoma cruzi B13 and cardiac myosin heavy chain . In: J Autoimmune . (2005) 24: pp. 111-117. PMID 15829403