Cells and organs of Immune system Parmar Krupal

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.

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.

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.

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

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.

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.

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.

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