Functions of Monocytes, Eosinophils, and Neutrophils

Monocytes and Macrophages

Monocytes feature a bean-shaped nucleus that occupies almost the entire cell. A monocyte is an immature cell in transit through the blood; it eventually migrates into tissues to transform into a mature macrophage. Consequently, macrophages and monocytes are the same cell type at different stages of maturation.

Functions of Monocytes

• Phagocytosis and antigen processing.
• Acting as Antigen-Presenting Cells (APC).
• Production of molecular mediators of the immune response (such as IL-1, IL-12, and TNF).

Tissue-Specific Conformations

Once monocytes pass from the blood into tissues, they lodge there and acquire different forms and names based on their location:

• Kupffer cells in the liver
• Epithelioid cells in granulomas
• Microglia in the Central Nervous System (CNS)
• Alveolar macrophages in the lungs
• Mesangial cells in the kidneys

Eosinophils and Parasitic Defense

Eosinophils are primarily stained with acid dyes containing eosin. Their granules stain a deeper red than those of other granulocytes. These cells are relatively scarce in the blood, typically representing no more than 3% of total leukocytes.

Roles and Molecular Composition

• Anti-parasitic function: They are capable of participating as regulatory cells in the inflammatory process.
• Major Basic Protein (MBP): Contained within the granules, this molecule is highly toxic and kills parasites.
• Histaminase: This enzyme neutralizes the action of histamine, an important component in inflammatory processes.

Neutrophils and Phagocytosis

The main feature of neutrophils is that their granular content does not stain with the dyes used in May-Grünwald Giemsa (MGG) staining. They constitute approximately 55% of total leukocytes.

Immune Response and Respiratory Burst

Their primary function is to eliminate waste produced during the immune response. They are capable of emitting pseudopodia to engulf and digest debris. By incorporating large amounts of enzymes, proteases, and myeloperoxidase, they trigger the respiratory burst.