Inclusion Bodies

Inclusion bodies are also known as cytoplasmic inclusions, cell inclusions, or elementary bodies. Some inclusion bodies examples are Negri bodies, Lewy bodies, etc. They are found floating in the cytoplasm. These are usually formed in the cells if they experience stress or are infected. Inclusion bodies class 11 is an important topic in the biology syllabus.

The general features of inclusion bodies depict the inclusion bodies as being acidophilic. Inclusion bodies can be classified as to where and how they are formed. In this article, we will read about the Inclusion bodies meaning, features, functions, and diseases involving inclusion bodies.

What are Inclusion Bodies?

Inclusion bodies are found in cells. They are formed when the pH of soluble fusion protein within cells decreases. Typically, they are formed in the virus-infected cells during infection. Inclusion bodies in cell are non-living and are composed of cellular metabolism by-products. Glycogen granules, phosphate granules, gas vacuoles, and cyanophycean granules are a few classic examples of inclusion bodies. Based on the cell type, inclusion body composition and function varies.

General Features of Inclusion Bodies in Cell

Common features of inclusion bodies are as follows:

• They are acidophilic.
• They do not have a membrane system and are freely suspended in cytoplasm.
• They appear as pink-coloured structures under the microscope on gypsum or methylene blue staining.
• They are made of virus antigens at the site of viral infection and indicate the degenerative changes in the cellular viral infection.

Functions of Inclusion Bodies

It performs various functions depending on the type of organism and the specific inclusion body. Some common functions of inclusion body are given below:

1. Protection: Inclusion bodies store harmful substances to prevent them from causing damage to the cell. For instance, polyphosphate granules in bacteria can sequester heavy metals, thereby protecting the cell from metal toxicity.
2. Storage: Inclusion bodies can serve as reservoirs for storing nutrients, energy reserves, or metabolic by-products.
3. Metabolic Regulation: Inclusion bodies can regulate metabolic pathways by isolating key enzymes or substrates. This helps in controlling the rates of certain metabolic processes within the cell.
4. Structural Support: Inclusion bodies can provide structural support to cells or tissues. For example, the crystalline inclusion bodies in cyanobacteria provide structural rigidity to the cell.
5. Protection Against Desiccation: Inclusion bodies like lipid droplets in some organisms serve to store lipids that can be used as a source of energy during periods of nutrient scarcity or to protect against desiccation.
6. Pathogen Defense: Inclusion bodies can sequester and degrade foreign materials, including pathogens, thereby contributing to the immune response of the organism.

Classification of Inclusion Bodies

Inclusion bodies can be present in prokaryotic and eukaryotic cells either in the cytoplasm or within the nucleus. Some inclusion bodies are formed during infection when the foreign microorganism infects the human cells. However, some inclusion bodies are formed during cell metabolism. Inclusion bodies in cell act as storehouses of certain metabolites or metabolic byproducts. Different types of Inclusion bodies are discussed further:

• Proteinaceous inclusion bodies: These are composed primarily of proteins. Examples include Lewy bodies in Parkinson’s disease and neurofibrillary tangles in Alzheimer’s disease.
• Viral inclusion bodies: These are formed during viral infections and contain viral proteins and nucleic acids. Examples include Negri bodies in rabies and Cowdry bodies in herpes simplex virus infections.
• Nuclear inclusion bodies: These are located within the nucleus of the cell. Examples include Cowdry type A bodies in herpes simplex virus infections.
• Cytoplasmic inclusion bodies: These are located within the cytoplasm of the cell. Examples include Lewy bodies in Parkinson’s disease.
• Neurodegenerative inclusion bodies: These are associated with neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease.
• Fibrillar inclusion bodies: These are composed of aggregated fibrillar proteins. Examples include neurofibrillary tangles in Alzheimer’s disease.
• Granular inclusion bodies: These are composed of granules or smaller particles. Examples include Negri bodies in rabies.
• Toxic inclusion bodies: These inclusion bodies may exert toxicity to the cell due to the accumulation of misfolded or aggregated proteins. Examples include Lewy bodies in Parkinson’s disease.
• Protective inclusion bodies: These inclusion bodies may serve a protective role by sequestering harmful proteins or viral particles. Examples include Mallory bodies in alcoholic liver disease.

Inclusion Bodies Examples

Some examples of each type of inclusion body is given as follows:

• Negri bodies: These are characteristic inclusion bodies found in the cytoplasm of infected neurons in rabies virus infection.
• Guarnieri bodies: These are eosinophilic cytoplasmic inclusion bodies seen in cells infected with smallpox (variola) virus.
• Polyhydroxyalkanoate (PHA) granules: These are inclusion bodies found in bacteria such as Escherichia coli during conditions of nutrient excess. They store carbon and energy in the form of PHA polymers.
• Lewy bodies: These are cytoplasmic inclusion bodies primarily composed of alpha-synuclein protein. They are characteristic of Parkinson’s disease and other neurodegenerative disorders.
• Neurofibrillary tangles (NFTs): These are intracellular inclusion bodies composed of hyperphosphorylated tau protein. They are a hallmark of Alzheimer’s disease and other tauopathies.
• Maurer’s clefts: These are inclusion bodies found in the cytoplasm of infected erythrocytes in Plasmodium falciparum, the causative agent of malaria. They are involved in protein trafficking and modification.
• Woronin bodies: These are specialized inclusion bodies found in filamentous fungi such as Neurospora crassa. They plug septal pores in response to cell injury, preventing cytoplasmic leakage.
• Droplets: Lipid droplets can also be considered inclusion bodies in fungal cells, serving as storage organelles for lipids.

Diseases Associated With Inclusion Bodies

Although storing cellular metabolites can serve a positive function for human cells, a deviation in natural balance can lead to certain disorders or health problems. Inclusion bodies cannot be confused with amyloid bodies which are also protein aggregates. The main difference is that amyloid accumulation involves polymerisation and can be intra or extracellular. However, inclusion bodies do not mandatorily need polymerisation and are specifically intracellular. Extracellular accumulations are not considered inclusion bodies.

Here, we have mentioned the human diseases involving inclusion bodies:

• Neuron and Muscle-Related Diseases: Occur when inclusion bodies or misfolded protein aggregates accumulate in the cytoplasm or nucleus of neurons. Examples include Huntington’s disease, Parkinson’s disease, dementia, and myositis.
• Erythrocyte-Related Diseases: RBCs do not contain inclusion bodies in general. But sometimes, they may accumulate in case of an existing pathological condition. Examples include alpha thalassemia and protozoan infections like malaria and babesemia.
• Viral infection-related diseases: These diseases occur due to the accumulation of basophilic or acidophilic inclusion bodies within plant or animal cells. Examples include smallpox, fowlpox, yellow fever and rabies.

Conclusion: Inclusion Bodies – Features, Classification and Examples

An inclusion body is a distinct structure found within cells that is often comprised of aggregated proteins, viral particles, or other substances. These bodies can vary widely in composition, size, and function, and they are observed across different organisms, including bacteria, viruses, fungi, protozoa, and human cells. Inclusion bodies are commonly associated with pathological conditions, but they can also serve physiological roles within cells like storage. They are an interesting topic of research and are still being studied to understand their mechanisms in depth.

FAQs on Inclusion Bodies

What are Inclusion Bodies Class 11?

Inclusion bodies are the tiny, floating particles within the cytoplasm of prokaryotic and eukaryotic cells. They are aggregates of protein or organic or inorganic molecules.

How are Inclusion Bodies Classified?

Inclusion bodies are diverse and can be classified based on location, composition and function.

• Based on the location: Intracellular and intranuclear inclusion bodies.
• Based on function: Infection or physiological inclusion bodies.
• Based on composition: Organic or inorganic inclusion bodies.

What is the Function of the Inclusion Body?

Inclusion bodies function as storage reservoirs of energy or carbon molecules as the glycogen or PHB bodies do.

Give Some Names of Inclusion Bodies in CNS.

Lewy bodies in Parkinson’s disease and dementia, Collin’s bodies in familial encephalopathy, inclusions in Huntington’s disease, and Bunina bodies in amyotrophic lateral sclerosis are some examples of inclusion bodies in CNS.

Can you Call Ribosomes as Inclusion Bodies?

Ribosomes cannot be considered as inclusion bodies. Ribosomes are non-membranous, granular structures composed of RNA and proteins.

How are Inclusion Bodies formed?

Inclusion Bodies are formed in the cells when pH increases in the cells containing a pool of soluble proteins. Besides, inclusion bodies are also formed in the cells during bacterial, viral or protozoan infections.

What are Inclusion Bodies in Protein Expression?

Inclusion bodies are dense protein aggregates formed during protein expression, often requiring isolation and refolding for protein recovery.