aggregates of stainable substances, usually proteins. They typically represent sites of viral multiplication in a bacterium
or a eukaryotic
cell and usually consist of viral capsid
Protein inclusion bodies are classically thought to contain misfolded protein
. However, this has recently been contested, as green fluorescent protein will sometimes fluoresce in inclusion bodies, which indicates some semblance of the native structure and researchers have recovered folded protein from inclusion bodies.
Mechanism of formation
from one organism are expressed in another the resulting protein sometimes forms inclusion bodies. This is often true when large evolutionary distances are crossed: a cDNA
isolated from Eukarya
for example, and expressed as a recombinant gene
in a prokaryote
risks the formation of the inactive aggregates of protein known as inclusion bodies. While the cDNA
may properly code for a translatable mRNA
, the protein
that results will emerge in a foreign microenvironment. This often has fatal effects, especially if the intent of cloning
is to produce a biologically active protein
. For example, eukaryotic
systems for carbohydrate
modification and membrane transport
are not found in prokaryotes
. The internal microenvironment
of a prokaryotic cell
) may differ from that of the original source of the gene
. Mechanisms for folding a protein
may also be absent, and hydrophobic residues
that normally would remain buried may be exposed and available for interaction with similar exposed sites on other ectopic
proteins. Processing systems for the cleavage and removal of internal peptides
would also be absent in bacteria
. The initial attempts to clone insulin
in a bacterium
suffered all of these deficits. In addition, the fine controls that may keep the concentration of a protein
low will also be missing in a prokaryotic cell
, and overexpression
can result in filling a cell with ectopic
protein that, even if it were properly folded, would precipitate
by saturating its environment.
Viral inclusion bodies
Examples of viral inclusion bodies include Negri bodies
(which are intracytoplasmic inclusion bodies of Rabies
virus in neurons
) and Cowdry bodies
(which are intranuclear inclusion bodies seen in Herpes Simplex Virus
Inclusion bodies in Erythrocytes
Normally a red blood cell
does not contain inclusions in the cytoplasm. However, it may be seen because of certain hematologic disorders.
There are three kinds of erythrocyte inclusions:
- Developmental Organelles
- Howell-Jolly bodies: small, round fragments of the nucleus resulting from karyorrhexis or nuclear disintegration of the late reticulocyte and stain reddish-blue with Wright stain.
- Basophilic stipplings - this stipplings is either fine or coarse, deep blue to purple staining inclusion that appears in erythrocytes on a dried Wright stain.
- Pappenheimer bodies - are siderotic granules which are small, irregular, dark-staining granules that appear near the periphery of a young erythrocyte in a Wright stain.
- Polychromatophilic red cells - young red cells that no longer have nucleus but still contain some RNA.
- Cabot Rings - ring-like structure and may appear in erythrocytes in megaloblastic anemia or in severe anemias, lead poisoning, and in dyserythropoiesis, in which erythrocytes are destroyed before being released from the bone marrow.
- Abnormal Hemoglobin Precipitation
- Heinz bodies - round bodies, refractile inclusions not visible on a Wright stain film. It is best identified by supravital staining with basic dyes.
- Hemoglobin H Inclusions - alpha thalassemia, greenish-blue inclusion bodies appear in many erythrocytes after four drops of blood is incubated with 0.5mL of Brilliant cresyl blue for 20 minutes at 37°C.
- Protozoan Inclusion