AUER CANES: CHARACTERISTICS AND PATHOLOGIES - BIOLOGY - 2025

The Auer rods or bodies are abnormal granules Auer lysosomal origin appearing within immature leukocytes myeloid series in pathological processes, specifically in acute myeloid leukemias.

Some authors call them Auer corpuscles, Auer sticks or Auer rods. They usually appear in M1, M2, M3, M4 acute myeloid leukemias (AML), among others. The name of these rods was placed in honor of the physiologist John Auer.

Smear from a patient with acute myeloid leukemia showing Auer's rods. Source: VashiDonsk from Wikipedia / Flickr

The precursors of granulocytic cells can present Auer bodies, especially in myeloblasts and promyelocytes. These bodies are nothing more than granules of the primary type or abnormal azurophils.

They are formed by the fusion of lysosomes, therefore they are rich in lysosomal enzymes and peroxidase. They also contain crystalloid precipitates of a protein nature.

Auer bodies are located in the cytoplasm of the cell and their observation helps in the diagnosis of myeloid leukemias, since they do not appear in lymphoid-type leukemias. Therefore, Auer bodies are a characteristic pathological sign of immature cells of the myeloid series.

characteristics

The fused azurophilic granules accumulate in an aligned manner in the cytoplasm of the cell and, consequently, acquire the shape of a rod or needle, hence the name of rods.

Cells containing Auer bodies are positive for myeloperoxidase and Sudan black B, which shows that they are cells of the myeloid lineage. Although more rare, Auer bodies may appear in precursors of the monocytic lineage (monoblasts) in AML (M5).

Auer bodies stain red or pink with Wright's stain, therefore they are easily visible, as they stand out in the strongly basophilic cell cytoplasm (grayish blue).

A cell can contain one or more Auer bodies, such that Auer rods can appear sparsely or abundantly.

Patients with cells with abundant Auer bodies are at risk for consuming coagulopathies and may end up with disseminated intravascular coagulation, for example acute promyelocytic leukemia (M3).

This is due to the release of a substance contained in the granules that is similar to tissue factor.

When this substance is released, it binds to factor VII of the coagulation cascade and lengthens the prothrombin times (PT) and partial thromboplastin (PTT). In addition, there is a low concentration of fibrinogen and a significant decrease in platelets.

Pathologies in which Auer's bodies are present

Auer bodies appear in myeloid-type leukemias and do not appear in lymphoid-type leukemias. Therefore, they are considered a pathognomonic sign of myeloproliferative or myelodysplastic disorders.

In this sense, the types of leukemias are mentioned according to the French-American-British Group (FAB) classification that can occur with the presence of Auer bodies.

Acute myeloblastic leukemia M1

It is characterized by presenting a higher percentage of blasts, which present an agranulated cytoplasm and a nucleus with 2 or 3 nucleoli.

While a very small percentage of the blasts may present few azurophilic granules or Auer rods. Both structures could even be present.

Myeloblastic leukemia with maturation (M2)

It is also called maturing or differentiated acute myeloid leukemia. A small percentage of promyelocytes and a higher proportion of mature cells of the granulocytic lineage can be seen in peripheral blood smears from these patients. Immature cells usually have Auer bodies within the cytoplasm.

Acute promyelocytic leukemia M3

It is characterized by the presence of abnormal promyelocytes with misshapen nuclei and grotesque and dysplastic granulations that may be accompanied by abundant Auer bodies. In this pathology there are important coagulation disorders, which distinguishes it from the rest of the leukemias.

Acute myelomonocytic leukemia M4

It is characterized by the homogeneous presence of both granulocytic and monocytic precursors in bone marrow with a proportion of promyelocytes and monocytes above 20%. Some promyelocytes may contain Auer bodies.

Erythroleukemia (M6a)

Abundant nucleated erythrocytes with few reticulocytes are seen in peripheral blood smear. Nucleated erythrocytes can be morphologically abnormal. There is an elevation of the myeloblasts and, they may or may not present Auer bodies.

Acute myeloid leukemia with dysplasia

It is characteristic of this type of leukemia that a bone marrow smear shows: Auer bodies, megaloblastoid maturation, as well as hyposegmentation of the nucleus and hypogranulation in the cytoplasm.

While peripheral blood smears usually show: circulating blasts, high percentage of monocytes, presence of hypogranular neutrophils, basophilia and pseudo-Pelger Huert forms

Chronic myeloid leukemia with blast transformation

It has 5 to 19% blasts in peripheral blood, and some promonocytes have Auer rods.

Other causes

It has been observed that a low percentage of patients with cancer disorders have developed a myeloid leukemia or a myelodysplastic syndrome after receiving treatment with chemotherapy and radiotherapy.

Especially those that have been treated with alkylating agents and epipodophyllotoxins.

Other situations in which it has been possible to observe Auer bodies is in patients who have suffered some type of bacterial infection or poisoning. They have also been observed in pregnant women and burns.

On the other hand, these cells are incapable of maturing on their own, so it was believed that Auer bodies could only be found in immature cells and that it was also impossible for these abnormal cells to return to normal. However, this theory was overthrown with the discovery of Dr. Degos.

He observed that patients with acute promyelocytic leukemia treated with trans-retinoic acid had a high remission rate, but the most curious finding was that the mature cells of these patients retained the pathognomonic mark of the disease (presence of Auer rods).. This suggests that the treatment makes the abnormal immature cells able to mature.

References

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