PLASMA CELLS: CHARACTERISTICS, FUNCTIONS AND DISEASES - BIOLOGY - 2025

The plasma cells, also known as plasma cells, are cells derived from a type of white blood cell (leukocyte) having the ability to synthesize antibodies and found in various tissues of mammals and other animals, which have important immunological functions.

The German anatomist Heinrich von Hartz-Waldeyer (1836-1921) was the one who first used the term "plasma cells" in 1875, to refer to the set of cells present in blood plasma.

Normal plasma cells (Source: Lydia Kibiuk (Illustrator) via Wikimedia Commons)

Later, in 1890, Santiago Ramón y Cajal described these cells as "cyanophilic cells", but it was not until 1891 that Paul Gerson Unna used the term "plasma cell" to refer to a specific group of cells that he observed in the lesions lupus vulgaris skin diseases caused by M. tuberculosis.

Today we refer to "plasma cells" when we speak of rounded or oval cells, with a basophilic cytosol, derived from B lymphocytes, which is why they are cells specialized in the synthesis of specific antibodies or immunoglobulins against certain antigens, even in the absence of these "stimulant" molecules.

They are extremely diverse cells and, although the pathologies related to them are rare, they are often characterized by the exaggerated multiplication of one of these, resulting in a large set of clonal cells that produce the same antibodies.

Characteristics of plasma cells

Plasma cells are found in the medullary cords of resting lymph nodes; they have also been identified in the marginal regions of the spleen and in some connective tissues of the human body.

Furthermore, these cells are also very abundant in the lamina propria of the intestinal mucosa. In fact, more than 80% of plasma cells have been related to lymphoid tissues associated with the intestines, where they are responsible for the synthesis of immunoglobulin A (IgA).

Photograph of a stained plasmocyte (Source: Guy Waterval via Wikimedia Commons)

They are cells with an eccentric nucleus, that is, it is displaced from the center. Heterochromatin is found inside its nucleus in a very particular way, some authors describe it as “the spokes of a thick truck wheel”. Surrounding the nucleus is what many have called a "perinuclear fold."

Its cytosol is moderately basophilic or amphophilic, that is, it can be stained by both acidic and alkaline dyes. On the other hand, its general shape is rounded or oval, with a diameter of 9-20 microns. In their cytosol, plasma cells have a prominent rough endoplasmic reticulum, to which multiple ribosomes are associated.

A small percentage of plasma cells have one or more highly distended rough endoplasmic reticulum cisternae, which contain a very dense material that is composed of "incomplete" immunoglobulin molecules.

Between the membranes of the endoplasmic reticulum of these cells are numerous mitochondria. They also have a large Golgi complex that forms a perinuclear “halo”.

A fully mature plasma cell does not express any type of immunoglobulin on its surface. Likewise, it loses the ability to express molecules of the class II major histocompatibility complex, which is why they do not function in the presentation of antigens.

Where do plasma cells come from?

Like the precursor cells of erythrocytes, megakaryocytes and cells of the myeloid lineage, plasma cells are cells belonging to one of the hematopoietic lineages, representing between 2% and 4% of the nucleated cells of the bone marrow.

These are derived from small B lymphocytes that have been activated, that is, they are terminal differentiating cells.

Antigen-mediated activation of mature B cells encourages the development of a "germinal center," which forms transient cells known as "plasmoblasts," capable of secreting antibodies as they divide.

Plasma cells (Source: Calicut Medical College via Wikimedia Commons)

In addition to plasmoblasts, extrafollicular short-lived plasma cells that secrete germline-specific antigens also differentiate from mature B cells. Plasmoblasts enter the bloodstream for a short period of time, until they reach the bone marrow, spleen, lymph nodes, or mucosa-associated lymphoid tissues.

These different anatomical regions provide plasmoblasts with the necessary factors to survive and differentiate into mature plasma cells with a longer life. Today it is known that plasma antibody titers are produced by these long-lived plasma cells.

Surface marker expression

Plasma cells co-express two molecules known as CD138 and CD38, which makes them easily identifiable by flow cytometry when bone marrow, peripheral blood, and other body tissues are studied.

CD138 and CD38 are part of a set of surface markers that cytologists use for the "immunophenotyping" of cells of the immune system. This set of markers is known as the “group of differentiation”, from the English Cluster of Differentiation and they are often surface proteins with specific functions.

When these cells become "malignant cells" due to some type of pathology, the expression of their surface molecules is altered and these are easily identifiable by the presence of molecules such as CD28, CD33, CD56 and CD117.

Features

Plasma cells or plasma cells can be defined as "a mature B cell type" that does not express antibodies on its surface, but does secrete them in large quantities.

From this perspective, it is logical to point out that they are cells of utmost importance for the immune system, especially for the adaptive or humoral response system.

After maturing from a B lymphocyte, these cells continually produce antibodies for months and even years, even in the absence of an antigenic stimulus, therefore they are essential for the body's protection against various invading pathogens.

Related diseases

Plasma cell-related diseases or disorders are not very common, but are generally associated with the exaggerated or uncontrolled multiplication of a single type of plasma cell.

The result of these disorders leads to the synthesis of large amounts of the same antibody (monoclonal), which many scientists have identified as the M protein.

Given that the uncontrolled division of these cells produces clones and since these clones produce the same type of antibody, the body's ability to respond to other infections decreases, which is why people with this type of pathology are more prone to other infections.

When the number of “abnormal” plasma cells increases considerably and they invade different organs and tissues, too much antibody can damage vital organs such as bones and kidneys.

The most common "plasma" pathologies are:

- Monoclonal gammopathy.

- Multiple myeloma.

- Macroglobulinemia (rare).

- Heavy chain diseases (rare).

References

1. Bayrd, ED, & Kyle, RA (1976). The monoclonal gammopathies: multiple myeloma and related plasma-cell disorders. Thomas.
2. Chen-Kiang, S. (2005). Biology of plasma cells. Best practice & research Clinical hematology, 18 (4), 493-507.
3. Lee, DS, Chng, WJ, & Shimizu, K. (2014). Plasma cell neoplasms: genetics, pathobiology, and new therapeutic strategies. BioMed research international, 2014.
4. Pellat-Deceunynck, C., & Defrance, T. (2015). The origin of the plasma-cell heterogeneity. Frontiers in immunology, 6, 5.
5. Ribatti, D. (2017). The discovery of plasma cells: an historical note. Immunology letters, 188, 64-67.
6. Shapiro-Shelef, M., & Calame, K. (2005). Regulation of plasma-cell development. Nature Reviews Immunology, 5 (3), 230.