Bovine mast cells: distribution, density, heterogeneity, and influence of fixation techniques

Area of Science:

• Immunology
• Cell Biology
• Veterinary Pathology

Background:

• Mast cell classification varies significantly across species (rodents, canines, humans), leading to confusion regarding mast cell heterogeneity.
• Species-specific data on mast cell distribution and types are crucial for accurate understanding and research.
• Previous studies lack comprehensive characterization of bovine mast cell subtypes and their distribution.

Purpose of the Study:

• To determine the physiological distribution of mast cell numbers and subtypes in various bovine tissues.
• To investigate the influence of different tissue locations, staining, and fixation methods on mast cell identification.
• To characterize bovine mast cells based on their protease content (tryptase and chymase).

Main Methods:

• Tissue samples were fixed using formalin or Carnoy's fluid.
• Mast cell numbers were quantified using a metachromatic staining method.
• Protease content was analyzed via double-enzyme-immunohistochemical staining to identify tryptase (T) and chymase (C) activity.

Main Results:

• Three mast cell subtypes were identified: T-mast cells, TC-mast cells, and C-mast cells.
• T-mast cells were the predominant subtype across most investigated bovine organs.
• Tryptase-positive mast cells were exclusively found in bovine skin and uterus, with no detectable chymase activity in these tissues.
• Carnoy's fluid fixation yielded a higher mast cell count but prevented the identification of chymase-positive cells, unlike formalin fixation.
• The three distinct mast cell subtypes were only observable in formalin-fixed tissues.

Conclusions:

• This study establishes distinct bovine mast cell subtypes (T-, TC-, C-mast cells) based on protease expression.
• The predominance of T-mast cells and the specific localization of tryptase-positive cells in certain bovine tissues highlight species-specific mast cell heterogeneity.
• Understanding these mast cell subtypes and their differential protease activities (tryptase vs. chymase) is essential for interpreting diverse inflammatory and tissue remodeling responses in bovines.