Granulocytes : Neutrophils/Eosinophils/Basophils

1. Granulocytes: Neutrophils/Eosinophils/Basophils • Classified according to cell morphology and cytoplasmic staining • Neutrophils: stains with BOTH acid and basic dyes • called ‘PMN’ for lobed nucleus; 50% of circ leukocytes • Eosinophils: stain with ACID dye (Eosin-red); bilobed nucleus; • 1-3% of leuko’s • Basophils: stain with BASIC dye (Methylene blue); <1% of • leuko’s

2. Neutrophils • Circulate in peripheral blood 7-10 hr before migrating into tissue; live only a few days • “front line of innate defense” • increased # (leukocytosis) used as an indicator of infection • extravasate in inflam rxn • attracted by chemotactic factors • active phagocytes; digestive enzyme held in 1° and 2° granules • Use both O2-dep and O2-indep digestive mech’s • Produce high levels of defensins

3. Eosinophils and Basophils Eosino’s • Like Neutrophils, function in phagocytosis • function vs. parasitic infections • contents of released granules damages parasitic membrane in ADCC • Non-phagocytic; function as “sirens” for inflam and allergy Baso’s

4. Dendritic cells (DC) • Resemble dendrites of nerve cells- hence the name • major role as APC  TH • 4 types: Langerhans Interstitial DC’s Myeloid DC’s Lymphoid DC’s • all with hi levels of MHC II and B7 receptors • follicular DC’s localized to follicles and have receptors for Ab’s

5. Organs of the Immune system Primary lymphoid organs: location of lymphocyte maturation and immunocompetence *bone marrow *thymus gland Secondary lymphoid organs: locations where Ag contacts lymphocytes ranges from a) diffuse groupings of lympho’s and MØ (in lungs + lamina propria of int. wall) to b) lymphoid follicles – aggregates of lymphoid cells cradled by draining lymph vessels to c) lymph nodes and spleen – highly organized organs

6. Primary lymphoid organs: • Thymus Gland – flat, bilobed organ just above the heart • -surrounded by a capsule divided into lobules by strands of conn tissue called trabeculae • -each lobule has a peripheral portion  Cortex • with immature T cells (thymocytes) + nurse cells • -each lobule has an inner portion  Medulla • all is embedded in a stroma containing DC + MØ’s • *thymus generates T cells with large diversity of TCR’s; destroys those T cells which react with self Ag’s and those which cannot recog Ag/MHC

8. Thymic function declines with age; max size at puberty- atrophies thereafter

9. Primary Lymphoid Organs: 2) Bone marrow – not site of B dev in all species -site of both origin and development of B cells -stromal cells secrete cytokines req’d for B cell devlpt -those B cells which react to “self” are destroyed

10. Lymphatic system • BP serves to push plasma thru thin capillary walls • This “interstitial fluid” bathes cells of tissues • some returns to capillaries, some flows into lymphatic capillaries to lymphatic vessels to lymph nodes, etc  to efferent lymph vessels to thoracic duct or right lymph duct where it (lymph) enters back into bloodstream and circulation • Foreign Ag gaining entry to lymph drainage is carried to local lymph nodes where it becomes trapped and presented to lymphocytes