Blood

OVERVIEW:

This is a summary of key concepts from the pre-recorded videos and arranged by session objective.

Peripheral blood smear: The staining on this sample shown above is called Wright’s Stain.   This stain is used for peripheral blood smears and it is similar to H&E in that it uses eosin as one of the dyes.  However, instead of hemotoxylin it uses methylene blue dyes.  As the image is scanned at an intermediate magnification, nucleated cells can be identified because of their basophilic nuclei. Below are images of leukocytes taken from this smear.

Optional activity:  You can practice looking at mature RBCs using a virtual microscope with guiding text in the right panel at this link (please don’t worry about learning the immature forms at this point).

Optional activity:  You can practice looking at platelets using a virtual microscope with guiding text in the right panel at this link.

Neutrophils-Polymorphonuclear leukocytes

No distinctively stained granules. “Neutral” to acidophilic or basophilic dyes.  Distinctive nuclear segmentation. The lower panel of images shows less mature neutrophils with less segmented nuclei. Remember that the nuclei of less mature neutrophils/polymorphonuclear leukocytes have less segmentation. “Shift to the left” of neutrophils in blood smear differential may be indicative of possible inflammatory response, when less mature neutrophils are recruited into the blood in response to systemic inflammatory stimuli.

An important concept is the “left shift” observed when mature neutrophils are depleted from fighting a severe infection.  Examine the band neutrophils and left shift phenomenon at this link.

Optional activity:  You can practice looking at mature neutrophils using a virtual microscope with guiding text in the right panel at this link (please don’t learn the immature forms except for band neutrophils at this point).

Eosinophils

Cytoplasmic granules are intensely eosinophilic.  Nuclei are bilobed.  The panel on the far right contains an eosinophil and a neutrophil so you can compare typical nuclear morphologies and cytoplasmic staining of the two cell types.

Optional activity:  You can practice looking at mature eosinophils using a virtual microscope with guiding text in the right panel at this link (please don’t worry about learning the immature forms at this point).

Basophil

Basophils are pretty infrequent in normal blood. (this is a reminder to know the relative abundance of nucleated blood cells in peripheral blood!). Similar to eosinophils, the basophil nucleus is bilobed. Because of the coarse basophilic cytoplasmic granules, the nuclear morphology of basophils may be difficult to discern.

Optional activity:  You can practice looking at mature basophils using a virtual microscope with guiding text in the right panel at this link (please don’t worry about learning the immature forms at this point).

Lymphocyte

Lymphocytes have relatively little cytoplasm compared to their nuclei, which are densely packed with chromatin and are very basophilic. In contrast to the granulocytes, which are post-mitotic by the time they reach the peripheral blood, lymphocytes retain the ability to undergo replication during an immune response (more on that later).  This means that the peripheral blood will contain lymphocytes of different size, depending on their replicative history (small, medium, and large lymphocytes).  This info is provided to you as an explanation for why you will see heterogeneous lymphocyte profiles in blood smears- you will not be required to make this subclassification of lymphocyte morphology.

Lymphocytes are a type of cell that you will find in lymphatic tissue sections throughout the body (some lymphatic tissue is encapsulated like seen in the link below, but often it is scattered, or diffuse, within a tissue).  Examine the lymph node at low magnification seen at this link to gain a sense of 1) increased cell density of lymphatic tissues (particularly because of the large amounts of lymphocytes), and 2) the basophilic staining properties of these tissues compared to the cells in the surrounding tissues.  Zoom in on the section to examine individual lymphocytes that are outside of the blood stream.

Optional activity:  You can practice looking at lymphocytes using a virtual microscope with guiding text in the right panel at this link.

Monocytes

Monocytes are macrophage precursors that circulate in the blood.  They can extravasate (leave the blood vessel to enter tissue compartments) to become tissue macrophages.  Like lymphocytes, they are mononuclear (not segmented or bilobed).  Monocytes are typically larger than lymphocytes and may have a cleft or notch in their nuclei.

Optional activity:  You can practice looking at monocytes using a virtual microscope with guiding text in the right panel at this link.

Some Abnormal Blood Cells:

Smear from patient with Chronic Myelogenous Leukemia (CML). The micrograph below highlights some differences from normal and serves to reinforce the expected representation of cells in a normal sample. Scanning this smear at intermediate magnification will demonstrate profiles of cells that resemble immature myeloid cells in the normal bone marrow but are not observed in normal peripheral blood. Lots of immature forms. Other common features in CML include variable elevation in peripheral blood basophils, elevated platelet counts  and alterations of erythropoiesis-reticulocytes and normoblasts in the smear.

Leukemic cells resembling normal myeloblasts and platelets (basophilic cell fragments in micrographs):

-Very large cells, abundant cytoplasm; nucleus not segmented; variably basophilic cytoplasm reflecting active protein synthesis, modest abundance of granules that stain indistinctly.

Elevated Number of Basophils in the Smear.  The most likely explanation if a patient presents with elevated basophil counts is CML.  Refer to a hematologist!

Basophils are more readily detected. Note the frequency of platelets in the smear.

Immature Erythrocytes in Peripheral Blood

Immature erythroid lineage cells are seen in the peripheral blood in some conditions like anemia. Also note the variability of erythrocyte diameter in the smears and the slightly elevated basophilia in some erythrocytes. What would be one interpretation of these findings related to erythrocytes?

Compare the blood smear of a patient with bacterial sepsis at this link to the case presented in the multiple choice question above.

Bone marrow

Stain information:  Hemotoxylin and Eosin

This is a plug of bone marrow that has been removed from surrounding bone before subsequent processing. Normally, surrounding bone would make identification of bone marrow trivial. Even without surrounding bone, bone marrow has some characteristic features. At this low magnification, note presence of scattered adipocytes that appear as white spots where tissue processing has extracted fats and lipid from adipocytes.

Slide 14:

The basophilia of bone marrow reflects the high density of nucleated cells with relatively little cytoplasm. Note that the cellularity of bone marrow is comprised of heterogeneous cells that reflect the active hematopoiesis occurring here and the different lineages of cells produced. You will see later that lymphoid tissue is also basophilic, but is of one predominant cell type-lymphocytes.  Several large polyploid megakaryocytes (the source of platelets) are indicated by yellow arrowheads. Adipocytes are indicated by asterisks. The eosinophilic structure at lower left is an artery (squamous endothelium forming the lumen and surrounded by smooth muscle. Hash mark is in the lumen.

Optional activity:  You can practice looking at megakaryocytes using a virtual microscope with guiding text in the right panel at this link.

Adipocytes are indicated by asterisks and a megakaryocyte is indicated by a yellow arrowhead. An irregularly shaped vascular sinusoid (a type of blood capillary in bone marrow) is outlined in black. Cells of the eosinophilic myeloid lineage can be picked out based on staining and some neutrophilic myloid cells can be identified based on nuclear morphology. Many of the cells with very small round condensed nuclei are normoblasts (nucleated immature RBC). One group is outlined in blue.

This is a sample of bone marrow with associated bone. The presence of spicules of trabecular bone (arrowheads) together with cortical bone and cartilage (arrow) suggests a vertebral body. In this sample, the presence of trabecular bone spicules is an important indicator that the basophilic tissue represents hematopoietic tissue.

The staining of this sample allows good discrimination between vascular sinuses (filled with blood-mostly RBC; outlined in black) and the surrounding tissue comprised of hematopoietic tissue and adipocytes. The more distal or terminal aspects of erythroid cell development can be seen to good advantage in this sample because these cells have very basic nuclei with eosinophilic cytoplasm. Chromatin of other lineages of cells and the earlier phases of erythroid lineage is not very condensed and doesn’t stain very well. These erythroblastic islands are circled in blue. A megakaryocyte is indicated with yellow arrow and some adipocytes are indicated by asterisks.