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 )
The HSC is considered the paradigmatic adult stem cell because it can differentiate into all the types of blood cells.
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