Cells of immune system

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1. CELLS OF IMMUNE SYSTEM:
Stem cells:
 The cells which develop into blood cells are called stem cells
process called haemopoiesis
 Undifferentiated embryonic cells
 Ability to divide into any type of blood cells said to be
pluripotent and totipotent
 Early embryonic stage originated in the yolk sac and migrate to
liver and then to bone marrow in adult
 the stem cells proliferate and differentiate under the influence of
colony stimulating factors
 the stem cells develop in three lines namely lymphoid lineage,
myeloid lineage and erythroid lineage
 lymphoid lineage;
 the stem cells develop into lymphoid progenitor ….further
develops into three groups of immune cells namely T
lymphocytes, B lymphocytes, and null cells


LYMPHOCYTES:
B LYMPHOCYTES:
 The lymphocyte that matures in bursa of fabricius or bone
marrow and that brings about humoral immunity is called B
lymphocytes
 Mononucleate, non granular
 Spherical or oval in shape diameter of 7 to 12um
 Large nucleus and a rim of cytoplasm
 They do not contain endoplasmic reticulum
 Consists of about 27%
 Found in blood and lymph,spleen, lymph nodes
 Involved in humoral immunity(produce antibodies)
 The B lymphocytes contain immunoglobulins on their surface
called surface immunoglobulins
 The immature B cells contains IgM on their surface and in
mature it contains both IgD and IgM

2.  Ia(immune associated) protein which binds with the Ia receptor
of the T lymphocytes
 Fc receptor to bind with the Fc fragment of the immunoglobulin
 CR1 and CR3 receptors of complement system
 Haemopoietic stem cells turn into lymphoid progenitor
differentiated into pre B cells and enter into bone marrow and
develops into B lymphocytes
 When there is proper antigen stimulation B cells are divided
into plasma cells and memory cells
Memory cells:
 Survive for a longer period of time and they respond quickly
and effectively during the subsequent similar antigenic
stimulation
 They bring about secondary immune response


PLASMA CELLS:
 End cells of B lymphocytes
 Eccentrically placed nucleus and cartwheel shaped
 Protein synthesizing machinery is well developed
 Filled completely with endoplasmic reticulum
 Is devoid of surface receptors
 Rich in immunoglobulins in the cytoplasm
 Russels bodies are observed in the cytoplasm
 Plasma cells do not divide and have half life of about two to
four days
T LYMPHOCYTES:
 Mononuclear non granular that matures in thymus
 Brings about cell mediated immunity
 Thymus dependent cells
 Have a large nucleus and a rim of cytoplasm
 Highly concentrated in the blood and spleen
 Contain T cell surface markers
 Erythrocyte receptor recognizes the sheep erythrocytes
 T cell antigen receptor recognizes both MHC I and II
 Ia protein receptor recognizes the immune associated protein

3.  Inter leukinrecpetors like IL 1 and IL2 are present on the T
cells
 They are different types of T cells
T helper cells:
 Regulatory cells
 Represented by Th
 Contain glycoprotein molecule called CD4 molecules on the
surface
 The HIV mainly infects the Th cells
 It secretes lymphokines which increases the release of B cells T
killer and T suppressor cells
 Also secrete macrophage migration inhibition factor …..which
activates macrophages to perform phagocytosis
T suppressor cells
 Regulatory cells
 Suppresses the function of the T killer cells and T helper cells
 Responsible for immune tolerance
T cytotoxic cells
 Also called effector cell or cytotoxic cells
 Contain CD8 glycoprotein on the surface
 It directly attack a cell and kill the virus infected cell
 Important role in destroying cancer cells
T delayed type hypersensitivity cells
 Similar to Th cells and bring macrophages to areas where
delayed hypersensitivity reaction occur
Null cells:
 Lymphocytes with cytotoxic property
 Neither B cell not T cell
 Two types
Natural killer cells:
 Large granular lymphocytes
 Kidney shaped nucleus
 They possess FC receptor for IgG and CR3 for complement
 Antibody independent ……kill the target cell
 Activated by interferons and interleukins

4. Killer cells;
 Antibody dependent cells
 They possess IgGrceptors for binding with IgG antibody

Myeloid lineage;
MONOCYTES:
 Mononuclear phagocytic leucocytes possessing an oval or
kidney shaped nucleus
 Granules in the cytoplasm
 Originated form the stem cells of bone marrow ……developed
into myeloid progenitor cells .turn into monoblasts…….become
promonocytes….monocytes
 Monocytes live only for 24hrs they leave the blood and migrate
into tissues where they enlarge and become macrophages
 Two types resident macrophages ( stationary and immobile) and
elicited macrophages( wandering cells)
 Based on the tissue they are kupffer cells ( liver)
 Alveolar macrophages (lungs)
 Peritoneal macrophages(peritoneal cavity)
 Microglial cells (nervous system)
 Giant cells (formed by the fusing of many macrophages)
Functions:
 Phagocytosis
 Antigen processing
 Antigen presentation
 Macrophages that present antigens to T helper cells by MHC II
 Macrophages that present antigens to T cytotoxic cells by MHC
I
 Secretion substances like components, hydrolytic enzymes,
interleukin-1

5. GRANULOCYTES:
 Are those leucocytes which have irregular shaped nuclei with
two or five lobes
 Granulated cytoplasm
 Granules of cytoplasmic matrix contain reactive substances that
kill microorganisms and enhance inflammation
 Granulocytes are also called polymorphonuclear leucocytes
BASOPHILES:
 Named because of their cytoplasm containing granules that
stain with basic dyes
 Possess bi lobed irregular shaped nucleus
 Are non phagocytic cells that function by releasing
pharmacologically active substances ( histamine,
prostaglandins, serotonin)
 0.4% white blood cells
 Preventing blood clotting because basophils contain heparin
 Mediating allergic reactions
 Basophils are also thought to play a role in causing the body to
produce the antibody called IgE
 Non motile and remain confined to the blood stream

6. EOSINOPHILS:
 Disease fighting white blood cells
 They are acidophilic leucocytes
 Named so eosin an acid due stains the granules of the cytoplasm
 Bi lobed nucleus
 The granulocytes are rich in hydrolytic enzymes
 2-5% of leucocyltes
 Increase in number of eosinophils is observed in allergic
reactions especially during infection with intestinal parasites
 At the time of parasite infection degranulation of eosinophils
occurs and hydrolytic componenets of the granules are released
which kill the parasite
 Are motile cells that migrate from blood stream into tissue
spaces

7. NEUTROPHILS:
 Forms the major part of the white blood cells
 Motile short lived cells with multi lobed nucleus
 Cytoplasm contain granules which do not take acidic or basic
strains called neutrophils
 Major function is phagocytosis
 First cell to arrive at infection site
 Important role in inflammatory response
 Use oxygen dependent and oxygen independent pathways to
generate antimicrobial substances
 Cytoplasm contain primary and secondary granules which
contain hydrolytic enzymes

Dendritic cells:
 0.2% of cells in blood
 Present in the spleen and lymph nodes
 They are antigen presenting cells
 Present th antigen to TH cells
 They contain FC receptor and class II MHC
 Long membrane extensions resembling the dendrites of nerve
cells

8. Langerhans cells;
 Present in the skin
 From skin they migrate into the spleen and lymph nodes
 They contain class I and II MHC molecules, FC and C3
receptor
 Present the antigen to T cell
Mast cells;
 Large tissue cells with basophilic granules in cytoplasm
 Similar to basophils
 Sessile and present in the tissues through out the blood
polymorphous nucleus
 Two types
mucosal mast cells;
 Found in the mucosa of the lung and gut
 These cells are dependent on T lymphocytes for differentiation
Connective tissue mast cells:
 These cells do not dependent on the T lymphocytes
 Granules of mast cells releases histamine, heparin, platelet,
leukotrienes and prostaglandins which bring about the
inflammatory and allergic reactions
Platelets:
 Nonnucleated cells of blood
 Spherical and colourless
 Derived from megakaryocytes of bone marrow
 They have class I MHC products and receptors for IgG
 Role in blood clotting
 Involved in immune response especially in inflammation

9.  They contain granules which secrete histamine and serotoin


Note:
 Granulocytes or polymorpho nucleate cells : neutrophils,
eosinophils, basophils
 Antigen presenting cells: macrophages, dendritic
cells,Langerhans cells
 Agranulocytes or Mononuclear cells; Tcells, B cells, NK cells ,
monocytes