Origin and functional role
Plasma cells do not exist in tissues initially in their mature form. The process of their formation is inextricably linked with the immune response. The parent cell for the formation of plasmocytes is always a B-lymphocyte.
For the transformation process to begin, the B-lymphocyte must undergo stimulation by a specific antigen. Upon receiving the appropriate signal, the lymphocyte dramatically reorganizes its metabolism and structure, transforming into a highly specialized «factory». The sole and primary function of this factory is the continuous and massive production of antibodies (immunoglobulins), which are essential for neutralizing foreign agents.
Cytoplasm and Brachet's method
Since antibodies are proteins by chemical nature, the plasma cell requires a powerful and voluminous apparatus for their synthesis. This explains the fact that the cytoplasm of plasmocytes is extremely rich in rough endoplasmic reticulum (rER) and a vast number of ribosomes.
In histological practice, for the precise identification of plasma cells, a special histochemical reaction is used to detect RNA — Brachet's method. This staining utilizes a combination of two dyes:
- Methyl green;
- Pyronin.
Due to the colossal concentration of ribosomal RNA (which is necessary for active protein synthesis), the cytoplasm of the plasmocyte avidly binds pyronin. This phenomenon is called pyroninophilia. As a result, under the microscope, the cytoplasm of the cell acquires a bright and saturated crimson color.
Characteristic morphology: nucleus and «hof»
When studying histological preparations, plasma cells are easily recognized by two specific morphological features concerning the arrangement of the nucleus and organelles:
- Eccentric nucleus. Unlike many other cells, the nucleus in a plasmocyte is never located strictly in the center. It is always displaced toward one edge of the cell (occupying an eccentric position).
- Light «hof». Against the background of the intensely crimson-stained cytoplasm, an unstained, visually light area stands out clearly in the perinuclear zone. This formation is called the «hof» (or perinuclear halo).
The light appearance of the «hof» is explained by the fact that there are virtually no ribosomes and RNA in this zone, so it does not stain with pyronin. This area is dedicated to other crucial organelles: centrioles and an extensive Golgi apparatus are localized here. The role of the Golgi apparatus in this zone is critically important — it is where the final packaging of newly synthesized antibodies occurs before they are secreted outside the cell.
Briefly: answers to topical questions
What specific chromatin arrangement is characteristic of the plasma cell nucleus?
The plasma cell nucleus is characterized by peripheral chromatin condensation.
Additionally, the plasmocyte is described as having a predominance of euchromatin due to its high synthetic activity. The nucleus is located eccentrically, meaning it is shifted toward the cell periphery.
In which organs and tissues are plasma cells predominantly localized?
Plasma cells are virtually absent in circulating blood.
The main localization sites of plasmocytes:
- Lymph nodes and spleen — main storage sites; in lymph nodes, plasmocytes can reside and function in the medullary cords.
- Red bone marrow — predominantly during a secondary immune response.
- Connective tissue of mucous membranes — for example, the intestines; plasmocytes are listed among the cells in the lamina propria of the large intestine.
- Intralobular connective tissue of large salivary glands — contains numerous plasma cells.
To easily recall the structure of a plasmocyte, imagine a ring with a large gemstone, where the stone is the peripherally shifted (eccentric) nucleus. Right next to the stone, the metal shines brighter — this is the light «hof» with the Golgi apparatus, and the ring itself is crimson due to the abundance of RNA.
Class and exam questions
From which cells and under what conditions do plasma cells form?
They form from B-lymphocytes. Triggering this process requires stimulation of the B-lymphocyte by a specific antigen.
Why does the cytoplasm of plasmocytes stain crimson according to Brachet's method?
The crimson color (pyroninophilia) is due to the binding of the pyronin dye to RNA. In plasmocytes, the RNA concentration is extremely high because of the abundance of ribosomes and rER necessary for antibody synthesis.
What is the light «hof» and what does it contain?
This is an unstained perinuclear zone against the background of crimson cytoplasm. It contains the centrioles and the Golgi apparatus, which is responsible for packaging the synthesized antibodies.
What else to study on this topic
- Mechanisms of B-lymphocyte stimulation by antigen
- The process of immunoglobulin translation on rER ribosomes
- The role of the Golgi apparatus in antibody packaging and secretion
- Chemical principles of Brachet's method and properties of pyronin
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