Ultrastructure of fibrillar granules in human neutrophils

Area of Science:

• Hematology
• Cell Biology
• Electron Microscopy

Background:

• Fibrillar granules (FGs) are primary neutrophilic granules characterized by clustered filaments.
• Neutrophils play a crucial role in immune response and are implicated in various hematological disorders.

Purpose of the Study:

• To investigate the presence and ultrastructure of fibrillar granules (FGs) in neutrophils from patients with chronic myeloproliferative disorders (CMPD).
• To characterize the composition of FG-filaments by determining their diameter and comparing them to known cytoskeletal filaments.

Main Methods:

• Bone marrow samples were obtained from 17 patients diagnosed with chronic myeloproliferative disorders (CMPD).
• Neutrophils were examined using high-resolution electron microscopy to identify and analyze fibrillar granules.
• The diameter of filaments within FGs was measured and compared to established filament types.

Main Results:

• FG-positive neutrophils were detected in 15 out of 17 CMPD patients, indicating a high prevalence.
• The frequency of FG-positive neutrophils varied among the patients.
• The filaments comprising FGs measured 7-8 nm in diameter, distinguishing them from intermediate filaments (typically 10 nm) and actin filaments (typically 7 nm, but with different structural properties).

Conclusions:

• Fibrillar granules (FGs) are a common finding in neutrophils of patients with chronic myeloproliferative disorders (CMPD).
• The unique 7-8 nm diameter of FG-filaments suggests they are composed of novel proteins or protein complexes, not previously identified cytoskeletal elements.
• Further research is warranted to elucidate the specific composition and function of these unique FG-filaments in the context of CMPD.