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1. Cells and organs of Immune
system
Parmar Krupal

2. Classification of organ of immune
system
• Primary Lymphoid Organs—Where Immune
Cells develop
• Site for development and maturation of lymphocytes.
• i.e. the bone marrow and the thymus—regulate the
development of immune cells from immature
precursors.

3. • Secondary Lymphoid Organs—Where the
Immune response Is Initiated
• Sites for lymphocytes and antigen interaction.
• i.e. including the spleen, lymph nodes, and specialized
sites in the gut and other mucosal tissues, MALT
Diagram of a lymph
node, showing the
flow of lymph
through the lymph
sinuses.

5. • hematopoietic stem cell (HSC) : all functionally
specialized, mature blood cells (red blood cells,
granulocytes, macrophages, dendritic cells, and
lymphocytes) arise from a single cell type.
• The process by which HSCs differentiate into mature
blood cells is called hematopoiesis.

6. • Two primary lymphoid organs are responsible
for the development of stem cells into mature
immune cells:
• the bone marrow,
– where HSCs reside and give rise to all cell types; and
• thymus,
– where T cells complete their maturation

7. • Stem cells are defined by two capacities:
• (1) the ability to regenerate or “self-renew”
• (2) the ability to differentiate into all diverse cell types.
• Types of stem cell
» Embryogenic stem cell
» Adult stem cell
capacity to generate every specialized cell type in an
organism( in other words, they are pluripotent )
have the capacity to give rise to the diverse cell
types that specify a particular tissue. Multiple adult organs
harbor stem cells (“adult stem cells”) that can give rise to
mature tissue-specific cells.

8. •Self-renewing hematopoietic stem cells give rise to lymphoid and myeloid progenitors.
• Most immune cells mature in the bone marrow and then travel to peripheral organs via
the blood. Some, including mast cells and macrophages, undergo further
maturation outside the bone marrow. T cells develop to maturity in the thymus.

11. • HSC can become a common myeloid-
erythroid progenitor (CMP), which gives rise
to all red blood cells (the erythroid lineage),
granulocytes, monocytes, and macrophages
(the myeloid lineage), or
• Either it can become a common lymphoid
progenitor (CLP), which gives rise to B
lymphocytes, T lymphocytes, and NK cells.

13. • Regulation of Lineage Commitment during Hematopoiesis
• Multiple genes that specify lineage commitment have been identified.
Many of these are transcriptional regulators
Transcription factor Importance
GATA-2 required form the development of all hematopoietic lineages. in
its absence animals die during embryogenesis.
Bmi-1 It is required for the self-renewal capacity of
HSCs, and in its absence animals die within 2 months of birth
because of the failure to repopulate their red and white blood
cells.
Ikaros is required for lymphoid but not myeloid development; animals
survive in its absence but cannot mount a full immune response
(i.e., they are severely immunocompromised).
Notch1 regulates the choice between T and B lymphocyte lineages