Reticulocytes are immature
red blood cells
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...
(RBCs). In the process of
erythropoiesis
Erythropoiesis (from Greek 'erythro' meaning "red" and 'poiesis' "to make") is the process which produces red blood cells (erythrocytes), which is the development from erythropoietic stem cell to mature red blood cell.
It is stimulated by decrea ...
(red blood cell formation), reticulocytes develop and mature in the
bone marrow
Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It is composed of hematopoietic ce ...
and then
circulate
''Circulate'' is the second solo album of Neil Sedaka after his 1959 debut solo album '' Rock with Sedaka''. ''Circulate'' was released in 1961 by RCA Victor and was produced by Al Nevins and Don Kirshner. Except for the title song "Circulate ...
for about a day in the blood stream before developing into mature red blood cells. Like mature red blood cells, in mammals, reticulocytes do not have a
cell nucleus
The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...
. They are called reticulocytes because of a reticular (mesh-like) network of
ribosomal
Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to fo ...
RNA
Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
that becomes visible under a
microscope
A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...
with certain
stains
A stain is an unwanted localized discoloration, often in fabrics or textiles.
Stain(s) or The Stain(s) may also refer to:
Color
* Stain (heraldry), a non-standard tincture
* Staining, in biology, a technique used to highlight contrast in samples
...
such as
new methylene blue
is an organic compound of the thiazine class of heterocycles. It is used as a stain and as an antimicrobial agent. It is classified as an azine dye, and the chromophore is a cation, the anion is often unspecified.
Applications
NMB is a staini ...
and
Romanowsky stain
Romanowsky staining, also known as Romanowsky–Giemsa staining, is a prototypical staining technique that was the forerunner of several distinct but similar stains widely used in hematology (the study of blood) and cytopathology (the study of di ...
.
Clinical significance
To accurately measure reticulocyte counts, automated
counters use a combination of laser excitation, detectors and a
fluorescent dye
A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with se ...
that marks
RNA
Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
and
DNA (such as
titan yellow
Titan yellow is a compound with formula C28H19N5Na2O6S4. It is a triazene
Triazene is an unsaturated inorganic compound having the chemical formula N3 H3. It has one double bond and is the second-simplest member of the azene class of hydro ...
or
polymethine
Polymethines are compounds made up from an ''odd'' number of methine groups (CH) bound together by alternating single and double bonds.Kachovski and Dekhtyar, ''Dyes and Pigments'', 22 (1983) 83-97. Compounds made up from an ''even'' number of meth ...
).
Reticulocytes appear slightly bluer than other red cells when looked at with the normal
Romanowsky stain
Romanowsky staining, also known as Romanowsky–Giemsa staining, is a prototypical staining technique that was the forerunner of several distinct but similar stains widely used in hematology (the study of blood) and cytopathology (the study of di ...
. Reticulocytes are also relatively large, a characteristic that is described by the
mean corpuscular volume
The mean corpuscular volume, or mean cell volume (MCV), is a measure of the average volume of a red blood corpuscle (or red blood cell). The measure is obtained by multiplying a volume of blood by the proportion of blood that is cellular (the hema ...
.
![Reticulocytes Human Blood Supravital Stain](https://upload.wikimedia.org/wikipedia/commons/9/99/Reticulocytes_Human_Blood_Supravital_Stain.jpg)
The normal fraction of reticulocytes in the blood depends on the clinical situation but is usually 0.5% to 2.5% in adults and 2% to 6% in infants. A reticulocyte percentage that is higher than "normal" can be a sign of
anemia
Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...
, but this depends on the health of a person's bone marrow. Calculating the
reticulocyte production index
The reticulocyte production index (RPI), also called a corrected reticulocyte count (CRC), is a calculated value used in the diagnosis of anemia. This calculation is necessary because the raw reticulocyte count is misleading in anemic patients. ...
is an important step in understanding whether or not the reticulocyte count is appropriate to the situation. This is often a more important question than whether the percentage is in the normal range; for instance, if someone is anemic but has a reticulocyte percentage of only 1%, the bone marrow is likely not producing new blood cells at a rate that will correct the anemia.
Immature reticulocyte fraction (IRF)
Reticulocytes at less mature levels can be detected by having higher intensity fluorescence regions. An increased immature reticulocyte fraction (IRF), specifically an IRF more than or equal to 0.23, together with an increased absolute reticulocyte count, generally indicates an adequate erythroid response to anemia.
[ ] An IRF of more than 0.23 but a subnormal or normal absolute reticulocyte count (with a corresponding reticulocyte production index of less than or equal to 2) is seen in for example acute infection, iron deficiency anemia, human immunodeficiency virus infection, sickle disease with crisis, pregnancy, and myelodysplastic syndrome.
An IRF of less than 0.23 is seen in diseases that lead to decreased erythropoietic activity, predominantly chronic renal insufficiency.
Development
The development begins with the expulsion of the normoblast nucleus, and is followed by loss of organelles and remodeling of the plasma membrane, giving rise to an
erythrocyte
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
.
Research
Reticulocytes are a valuable tool for biologists who study
protein translation
In molecular biology and genetics, translation is the process in which ribosomes in the cytoplasm or endoplasmic reticulum synthesize proteins after the process of transcription of DNA to RNA in the cell's nucleus. The entire process is ...
. Reticulocytes are unusual among cells in that they contain all of the machinery necessary to translate proteins but lack a nucleus. Since a cell's nucleus contains many components that make studying translation difficult, these cells are quite useful. Scientists can collect reticulocytes from animals such as rabbits and extract the
mRNA
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein.
mRNA is ...
and translation enzymes to study protein translation in a
cell-free,
in vitro
''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
system, allowing greater control over the environment in which proteins are being synthesized.
References
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Blood cells
Human cells