Alkaline phosphatase activity in phagocytizing granulocytes: a backscattered electron imaging study

Area of Science:

• Cell Biology
• Microscopy Techniques

Background:

• Alkaline phosphatase activity is crucial in cellular functions.
• Detecting enzyme activity in human polymorphonuclear leukocytes (PMNs) is challenging due to small lead depositions.
• Scanning electron microscopy (SEM) in backscattered electron imaging (BEI) mode offers potential for high-resolution imaging.

Purpose of the Study:

• To develop and validate a method for visualizing alkaline phosphatase activity in human PMNs using SEM-BEI.
• To identify distinct phases of the phagocytic sequence by observing lead precipitate patterns.

Main Methods:

• Utilized scanning electron microscopy (SEM) in backscattered electron imaging (BEI) mode.
• Employed a lead method to detect alkaline phosphatase activity.
• Incubated human PMNs with latex particles to enhance precipitate visibility.

Main Results:

• SEM-BEI successfully visualized lead precipitates indicative of alkaline phosphatase activity in human PMNs.
• Incubation with latex particles led to well-evident lead precipitates, aiding in the identification of phagocytic stages.
• Observed irregular depositions suggested secondary granule aggregation near phagocytic vacuoles.
• Homogeneous, round precipitates, larger than latex particles, likely represent fused vacuoles containing the enzyme.

Conclusions:

• SEM-BEI, combined with latex particle incubation, is effective for visualizing alkaline phosphatase activity in human PMNs.
• This method allows for the identification of different stages of phagocytosis based on enzyme localization and precipitate morphology.
• The findings provide insights into the dynamic process of granule fusion and enzyme release during phagocytosis.