Inclusion Bodies

What are Cell Inclusions?

If someone questions what are cell inclusions or what are inclusion bodies, the answer to both will be the same. Also known as inclusion bodies, these elementary bodies  are cytoplasmic inclusions or nuclear aggregates of stable substances like proteins. They freely suspend and float within the cytoplasmic matrix and can also be called cytoplasmic inclusions. They are usually sites of viral multiplication, thus in a bacterium or eukaryotic cell, therefore, are also referred to as viral inclusion bodies that consist of viral capsid proteins. Inclusion bodies can be an indication of certain diseases like Herpes, Parkinson’s disease, Measles, Rabies and Dementia.

Features of Inclusion Bodies

  • These act as reserve deposits.
  • Plenty nutrients can be stored in them by the cells and utilize when there is deficiency in the environment.
  • Some of the inclusion bodies in bacteria are very common in a wide variety.
  • Cell inclusions are generally acidophilic.
  • These can also be present as crystalline aggregates of virions.
  • Represent degenerative changes produced by a viral infection.
  • These are made of virus antigens present at the site where synthesis of virus takes place.
  • These can be observed as pink structures under microscope when stained with gypsum or methylene blue dye.

Classification of Inclusion Bodies

  • Metachromatic Inclusions – Some of the large cell inclusions that sometimes stain red with blue dyes like methylene blue are called metachromatic inclusions. These consist of granules that consist of starch and glycogen. In the presence of iodine, the glycogen granules appear reddish brown in colour and the starch granules appear blue.
  • Lipid Inclusions – These appear in various species of Bacillus, Mycobacterium, Azotobacter, and other genera and act as lipid storage material. These can be observed when cells are dyed with fat soluble dyes like Sudan dyes.
  • Sulphur Granules – These derive energy by oxidizing sulphur and sulphur containing compounds. They may deposit sulphur granules in the cell that serve as an energy reserve.
  • Carboxysomes – These inclusions contain the enzyme ribulose 1, -5 diphosphate carboxylase. Bacteria use these for a source of carbon for carbon dioxide fixation during photosynthesis.
  • Magnetosomes – Some bacteria orient themselves within a magnetic field due to the presence of magnetosomes. Magnetosomes are intracellular inclusion bodies or particles of iron oxide mineral called magnetite (Fe3O4). A magnetosome is enclosed by a thin membrane composed of protein, phospholipid and glycoprotein. It imparts a magnetic dipole on a cell allowing itself to exhibit magnetotaxis which is the process of migrating along the earth’s magnetic field. It is found in many aquatic organisms.

Based on the location, either at the nucleus or cytoplasm or at both of these cell organelles, we can classify inclusion bodies in the following categories:

  • Intranuclear cell inclusions.
  • Infection inclusion bodies.
  • Intracytoplasmic inclusion bodies.
  • Physiological inclusion bodies.

Inclusion bodies can be present in a bacterium or eukaryotic cell in the form of cystic lesions, fungal infections, virus infected cells, bacterial infections, autoimmune diseases, neoplasms and blood dyscrasias.
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Examples of Viral Inclusion Bodies

  • Acidophilic Intracytoplasmic Inclusion Bodies (eosinophilic)

Eg: Negri bodies in Rabies
Paschen bodies in Smallpox
Bollinger bodies in fowlpox

  • Acidophilic Intranuclear Inclusion Bodies (Eosinophilic)

Eg: Torres bodies in Yellow Fever
Cowdry type A in Herpes simplex virus
Cowdry type B in Polio and Adenovirus

  • Intranuclear Basophilic Inclusions

Eg: Cowdry type B in Adenovirus
Owl’s eye appearance – Cytomegalovirus

  • Both Intranuclear and Intracytoplasmic

Eg: Warthin-Finkeldey bodies in Measles

  • Viral Inclusion Bodies in Plants

Eg: Virus particles in Cucumber mosaic virus
Some of the Diseases that Involve Inclusion Bodies

  1. Inclusion body myositis which affects muscle cells.
  2. Amyotrophic lateral sclerosis that affects motor neurons.
  3. Dementia with lewy inclusions that affect cerebral neurons.

How to Prevent the Formation of Inclusion Bodies?

The cell inclusions are made of denatured aggregates of proteins (inactive), and several techniques have been developed to prevent the inclusion bodies formation. These help in the solubilisation and recovery of active proteins. The techniques are mentioned as follows:

  • Usage of weaker promoters to slowing down the rate of protein expression.
  • Using low copy number plasmids.
  • Co-expression of chaperone.
  • Using specific E.coli strains.
  • Fusing the target protein with a soluble partner.
  • Lowering of the expression temperature.

FAQ (Frequently Asked Questions)

  1. Define Inclusion Bodies. Cite Some Inclusion Bodies Examples.

Ans. Non-living materials found inside a bacterial cell are called  inclusion bodies. Some of the examples include gas vacuoles, inorganic inclusions present as granules like iron and sulphur granules, food reserve inclusion bodies that are responsible for food storage (eg: lipid globules and protein granules.

  1. Mention the Difference Between Cell Organelles and Cell Inclusions?

Ans. Cell organelles are the living components present in the cytoplasm of a cell, examples include mitochondria, ribosome, chloroplasts, ER, Golgi body, etc. Cell inclusions are the non-living components of the cytoplasm and examples include reserve food, excretory/secretory products and mineral matter.

  1. What are Ribosomes and Inclusion Bodies?

Ans. Ribosomes are attached to the plasma membrane of the cell and are the site of protein synthesis. In prokaryotes, it consists of two subunits 50 S and 30 S that form 70 S prokaryotic ribosomes. These are 15 to 20 nanometer in size, non-membrane bound bodies and several ribosomes get attached to the mRNA to form a chain called polyribosome or polysome.
Inclusion bodies are the reserve material found in the prokaryotic cells, stored in the cytoplasm. These can be cyanophycin granules, gas vacuoles, phosphate granules or many others. These are non-membrane bounded bodies and present freely in the cytoplasm.

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