GRANULOCYTES,types of granulocytes

 

  granulocytes

• Granulocytes have irregularly shaped nuclei with two to five lobes.
• Their cytoplasm has granules that contain reactive substances that kill microorganisms and enhance inflammation.

  Three types of granulocytes exist:   1. Basophils                                                                                   

                                                            2.Eosinophil

                        

                                                            3. Neutrophils 

1. Basophils  

•        Basophils (Greek basis, base, and philein, to love) have irregularly shaped nuclei with two lobes.
• The granules contain histamine and other substances similar to those in mast cells.
• However, basophils arise from a different cellular lineage
• basophils tend to infiltrate specific tissue sites rather than circulate through the bloodstream.
• Basophils are also important in the development of allergies and hypersensitivities

 2.Eosinophil

• Eosinophils have a two lobed nucleus connected by a slender thread of chromatin.
• Eosinophil granules contain hydrolytic enzymes (nucleases,

glucuronidases, and peroxidases), and major basic protein.

• It circulate in low numbers and migrate from the bloodstream into tissue spaces, especially mucous membranes, when recruited by soluble chemotactic mediators.
• They are important in the defense against protozoan and helminth parasites, mainly by releasing enzymes, cationic peptides and reactive oxygen species into the extracellular fluid.
• These molecules damage the parasite's plasma membrane, killing it.
• Eosinophils also play a role in allergic reactions, as they have granules that contain histaminase and aryl sulphatase, down regulators of the inflammatory mediators histamine and leukotrienes, respectively.
• Thus their numbers circulating in the bloodstream often increase during

allergic reactions, especially type l hypersensitivities

 3.Neutrophils 

• Neutrophils are highly PHAgocytic cells with a nucleus that has

three to five lobes connected by slender threads of chromatin .

• Because of the irregularly shaped nuclei, neutrophils are also called

polymorphonuclear neutrophils, or PMNs.

• Neutrophils have inconspicuous organelles known as primary and secondary granules.
• Primary granules contain peroxidase, lysozyme, defensins, and various hydrolytic
• enzymes
• secondary granules have collagenase, lactoferrin, cathelicidins, and lysozyme. 
• These enzymes and other molecules help digest foreign material after it is phagocytosed.
• Neutrophils also use oxygen-dependent and oxygen-independent Pathways that generate additional antimicrobial substances to kill ingested microorganisms.
• Mature neutrophils leave the bone marrow and circulate in blood so they can rapidly migrate to a site of tissue damage and infection, where they become the principal phagocytic and microbicidal responders.
• Neutrophils have toll-like pattern recognition receptors (PRRs), as well as receptors for antibodies and complement proteins, so that PAMPs and opsonize particles,respectively, can be more readily phagocytosed.
• PRRs bind to specific patterns that characterize microbial macromolecules and that their binding upregulates transcription pathways for phagocytosis
• Neutrophils have a limited life span that shotens upon activation of the phagocytic
• processes.