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 710 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
Eosino’s
• Like Neutrophils, function
in phagocytosis
• function vs. parasitic
infections
• contents of released
granules damages parasitic
membrane in ADCC
Baso’s
• Non-phagocytic; function
as “sirens” for inflam and
allergy
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
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