PHAGOCYTOSIS

Dr AnuPriya J

Scheme

• Definition • Phagocyte – cell types• Steps of phagocytosis• Summary

Phagocytosis

• Phagein = "to devour", kytos = "cell“, osis = “process” (from Ancient Greek)

• Phagocytosis is the process of engulfment and destruction of solid particles such as bacteria, dead tissue and foreign particles by the cells.

Phagocytes

• The cells performing phagocytosis are called phagocytes.

The cell types are• Neutrophils• Monocytes and• Macrophages

Steps

1. Margination 2. Diapedesis 3. Chemotaxis 4. Opsonization → attachment stage5. Engulfment stage 6. Secretion (degranulation) stage7. Degradation stage

Margination

Diapedesis

Chemotaxis

Chemotaxis

Potent chemotactic substances or chemokines are

• Leukotriene B4 (LT-B4)• C5a, C3a• Cytokines

• Opsonization refers to the process of coating of bacteria by the opsonins.

• The opsonin coated bacteria gets attached to the surface of phagocyte through the opsonin receptors.

• The principal opsonins are IgG opsonin and C3b opsonin.

Opsonization → Attachment stage

Engulfment stage

Pseudopodia

Engulfment stage

Phagocyte Lysosome

Degranulation stage

• Release of lysosomal enzymes into the vesicles

Degradation stage

• Oxygen dependent bactericidal mechanism mediated by oxidizing agents.

• Oxygen independent bactericidal mechanism mediated by lysosomal enzymes.

SUMMARY

1. Margination 2. Diapedesis 3. Chemotaxis 4. Opsonization → attachment stage5. Engulfment stage 6. Secretion (degranulation) stage7. Degradation stage

THANK YOU

Engulfment

• Formation of cytoplasmic pseudopods by the phagocytes around the bacteria.

• The bacteria is endocytosed and is contained in a vesicle thus forming a phagosome

• The phagosome fuses with nearby lysosome to form phagolysosome.