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

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

Eosinophils and Basophils• 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

Eosino’s

Baso’s

Dendritic cells (DC)• Resemble dendrites of

nerve cells- hence the name

• major role as APC TH• 4 types: Langerhans

Interstitial DC’sMyeloid DC’sLymphoid DC’s

• all with hi levels of MHC II and B7 receptors

• follicular DC’s localized to follicles and have receptors for Ab’s

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

Primary lymphoid organs:1) 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

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

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

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