Granulocytes vs agranulocytes
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Granulocytes vs Agranulocytes: A Comparative Analysis
Introduction to Granulocytes and Agranulocytes
Granulocytes and agranulocytes are two primary types of white blood cells (WBCs) distinguished by the presence or absence of granules in their cytoplasm. Granulocytes, also known as polymorphonuclear leukocytes, contain granules and include neutrophils, eosinophils, and basophils. Agranulocytes, or mononuclear leukocytes, lack these granules and consist of lymphocytes and monocytes5.
Morphological Characteristics
Granulocytes
Granulocytes are characterized by their granular cytoplasm and multi-lobed nuclei. They can be further subdivided based on the staining properties of their granules:
- Neutrophils: Contain neutral-staining granules.
- Eosinophils: Contain granules that stain with eosin.
- Basophils: Contain granules that stain with basic dyes5.
In mollusks, granulocytes are identified by their cytoplasmic granules and are further categorized into subtypes based on size and granule distribution. For instance, in the mussel Mytilus galloprovincialis, granulocytes make up about 22% of hemocytes and are more prevalent under hypoxic conditions1. Similarly, in the gastropod species Trachea vittata, granulocytes are divided into three sub-categories: Progranulocytes, basophilic granulocytes, and eosinophilic granulocytes2.
Agranulocytes
Agranulocytes lack visible granules in their cytoplasm and have a large nucleus-to-cytoplasm ratio. They include:
- Lymphocytes: Small cells with a large, round nucleus.
- Monocytes: Larger cells with a kidney-shaped nucleus5.
In mollusks, agranulocytes are the predominant hemocyte type, comprising about 78% of the hemocytes in Mytilus galloprovincialis1. They are further divided into hyalinocytes and lymphoid hemocytes based on their size and nuclear-cytoplasmic ratio4.
Functional Roles
Granulocytes
Granulocytes play a crucial role in the immune response. They are the primary phagocytic cells, responsible for engulfing and destroying pathogens. In the oyster Crassostrea gigas, granulocytes are the main immunocompetent hemocytes, exhibiting high phagocytic activity, lysosome activity, and production of reactive oxygen species (ROS) and nitric oxide (NO)3. Similarly, in the freshwater mussel Cristaria plicata, granulocytes are efficient in phagocytizing yeast and bacteria4.
Agranulocytes
Agranulocytes are involved in various immune functions, including the production of antibodies and the regulation of immune responses. In mollusks, agranulocytes produce significantly less ROS compared to granulocytes1. They also exhibit phagocytic activity, although to a lesser extent than granulocytes. For example, in the invasive apple snail Pomacea canaliculata, agranulocytes show phagocytic responses to microorganisms, albeit with a lower phagocytic index compared to granulocytes6.
Response to Environmental Stress
Granulocytes and agranulocytes respond differently to environmental stress. Under hypoxic conditions, the number of granulocytes in Mytilus galloprovincialis increases, while the number of agranulocytes decreases. This shift is accompanied by changes in ROS production, with granulocytes showing decreased ROS levels under hypoxia1.
Conclusion
Granulocytes and agranulocytes are essential components of the immune system, each with distinct morphological and functional characteristics. Granulocytes are the primary phagocytic cells and are highly active in producing cytotoxic agents, while agranulocytes play a significant role in immune regulation and antibody production. Understanding the differences between these cell types is crucial for comprehending their roles in health and disease.
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Most relevant research papers on this topic
Morphological and functional characterization of hemocytes in cultivated mussel (Mytilus galloprovincialis) and effect of hypoxia on hemocyte parameters
Hypoxia in cultivated mussels changes hemocyte composition, increasing granulocytes and decreasing agranulocytes, without causing hemocyte mortality or proliferation.
Non-RCT
Animal StudyCategorization of hemocytes of three gastropod species Trachea vittata (Muller), Pila globosa (Swainson) and Indoplanorbis exustus (Dehays).
Hemocytes in Trachea vittata, Pila globosa, and Indoplanorbis exustus are divided into two types: agranulocytes and granulocytes, with granulocytes categorized into three sub-categories based on cell dimensions, nu
The granulocytes are the main immunocompetent hemocytes in Crassostrea gigas
Granulocytes are the main immunocompetent hemocytes in oyster C. gigas, with granulocytes playing a key role in phagocytic and encapsulating functions, and mainly expressing immune related genes.
In Vitro Study
Highly CitedMorphology and phagocytic ability of hemocytes from Cristaria plicata
Small granulocytes are more efficient in phagocytic activity than large granulocytes and hyalinocytes, with water temperature significantly affecting their phagocytic ability.
Immune Defenses of the Invasive Apple Snail Pomacea canaliculata (Caenogastropoda, Ampullariidae): Phagocytic Hemocytes in the Circulation and the Kidney
The apple snail Pomacea canaliculata has a unique immune system with phagocytic hemocytes in the circulation and kidney, which may play a role in defending against microorganisms.
In Vitro Study
Rigorous JournalGranulocyte-Colony-Stimulating Factor Effectively Shortens Recovery Duration in Anti-Thyroid-Drug-Induced Agranulocytosis: A Systematic Review and Meta-Analysis
G-CSF significantly shortens recovery duration in patients with anti-thyroid drug-induced agranulocytosis compared to non-G-CSF treatment.
Meta-AnalysisA comparative analyses of morphological variations, phagocytosis and generation of cytotoxic agents in flow cytometrically isolated hemocytes of Indian molluscs.
Hemocytes in Indian molluscs show diverse morphological variations, phagocytic functions, and cytotoxic agent production, potentially due to species-specific responses and adaptation to different ecological niches.
Effects of Genetics and Anesthesia Upon Granulocyte and Agranulocyte Levels in Seven Inbred Mouse Strains
Genetic differences and anesthesia contribute to variations in granulocyte and agranulocyte counts in inbred mouse strains, but these differences do not appear to be related to other physiological characteristics.
Non-RCTAnimal StudyGranulocyte colony-stimulating factor (G-CSF) does not improve recovery from antithyroid drug-induced agranulocytosis: a prospective study.
G-CSF treatment is generally ineffective for antithyroid drug-induced agranulocytosis, as it does not improve recovery time compared to antibiotic therapy alone.
RCTHighly Cited