IMMUNOLOGY

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Cells of the Immune system

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Stem cells

The cells which develop into the blood cells are called Stem cells

They are Undifferentiated embryonic cells

They have the ability to develop into any type of Red blood cells. So they are said to be Pluripotent and Totipotent

The stem cells develop in three lines, namely lymphoid lineage, Myeloid lineage and Erythroid lineage

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Stem cell

Myeloid lineage

Lymphoid lineage

Erythroid lineage

RBC

Erythropoisis

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Lymphoid lineage

Lymphoid Progenitor

T-Lymphocytes B-Lymphocytes Null cells

Natural Killer cells Killer cells

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Myeloid lineage

Polymorpho nuclear

leucocytes

Monocytes

1. Eosinophils

2. Basophils

3. Neutrophils

4. Mast cells

5. APC

6. Megakaryocytes Platelet

Macrophages (MΦs)

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Lymphocytes

Lymphocytes are the “Central cells of the immune system”, responsible for acquired immunity & the immunological attributes of diversity, Specificity, many and self / nonself recognition.

Lymphocytes constitute

20% to 40% body’s WBC

90% cells in the lymph

Lymphocytes are subdivided into THREE populations

B-Cells, T-Cells, Null cells

Lymphocytes are mononucleate, nongranular leukocytes of lymphoid tissue, participating in immunity.

They are found in blood, lymph, and lymphoid tissues such as Spleen, lymph nodes, tonsils, payer's patches, appendix.etc.

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B-Lymphocytes The letter “B” designated from its site of maturation:

Bursa of fabricus in birds

Bone marrowin mammalian species

B-lymphocytes carries out “Humoral immune response” by producing antibodies.

Each of the cell contains approximately 1.5X105 molecules of antibody on the membrane of a single B-cell has an identical binding site for antigen

B-lymphocytes are stimulated by TH-lymphocytes

When the antigen stimulate, the B-cell divides repeatedly & differentiate over a 4 to 5 day period, generating a population of Plasma cell and Memory cell.

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T-lymphocytes

The letter “T” designates from its site of maturation in the

The T-cell receptors on their membrane surface (cell markers), which belongs to an important group of molecules known as

“Major Histocompatibility Complex (MHC).

The T-lymphocytes can be divided into THREE types

1) T-helper cells

2) Cytotoxic T-cells

3) Suppressor T-cells

“Thymus”

T-Cells regulate the “Cell mediated immunity”

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TH- lymphocytes

1. The T-cells interact with MHC-II molecules, present on the surface of the macrophage surface.

2. The cells produce variety of soluble factors known as “Cytokines”.

3. The cytokines increase the response of B-cells, T-killer cells and T- suppressor cells.

4. The lymphocytes also secrete another lymphokine called “Macrophage Migration inhibition factor”

Cytotoxic T-cells

1. The cells clonally express a large number of differentiate surface markers

2. These cells attack infected cells and cancer cells

3. The cells discharge a protein called “Perforin”, which lyses the infected cell.

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Null cells

1. Null cells are the small group of lymphocytes in the peripheral blood do not express the membrane in nucleus & receptors that distinguish T & B-cells.

2. Null cells fail to synthesize Immunoglobulin because these cells do not produce “Antigen-binding receptors”.

There are TWO types of null cells namely,

1. Natural Killer Cells (NK cells)

2.Killer Cells (K cells)

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1. Natural Killer Cells (NK cells)

• Natural killer cells form the third population of lymphocytes.

• NK cells have a Kidney shaped nucleus.

• Cell surface possess FC receptors for Ig and CR3 receptor for complement.

• They destroy the cancer cells and cells infected with herpes and mumps virus.

• They do not need antibody for activity.

• They are activated by Interferon-1 and Interferon-2

• They recognize altered cell surface and bring about cytolysis and cytotoxicity. www.BiochemDen.in

2.Killer cells (K cells):

•They are antibody dependent cells.

•These cells possess Fc receptors for binding with IgG antibodies.

•It is termed as “Antibody-Dependent Cell-mediated Cytotoxic reaction (ADCC)”

•The cells kill a variety of cells such as tumor cells, Bacteria, viruses, fungi and parasites.

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Myeloid lineage

Polymorpho nuclear

leucocytes

Monocytes

1. Eosinophils

2. Basophils

3. Neutrophils

4. Mast cells

5. APC

6. Megakaryocytes Platelet

Macrophages (MΦs)

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Polymorpho Nuclear Leucocytes

1. Eosinophils:

1. Eosinophilic cells constitute about 2 to 5% of WBC.

2. These are acidophilic leukocytes and are called eoisinophils.

3. Eosinophils has a bilobed nucleous & granulated cytoplasm that stains with the acid dye “EOSIN” red.

4. It play a significant phagocytic role like Macrophages.

5. In allergic conditions the cell count will increase.

6. Granules present in the cells & it contains hydrolytic enzymes.

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2. Basophils

1. Basophils constitute about 0.4% of white blood cells.

2. The basophilic granules are believed to contain HEPARIN.

3. It has a lobed nucleus and heavily granulated cytoplsm that stains with the basic dye “Methylene blue”

4. The cells release pharamalogically agents like Histamine, Seratonine, platelet activating factor and vasoactive amines at inflammation regions.

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3. Neutrophils:

1. Neutrophils constitutes about 40 to 75% of WBC cells.

2. It has a multi-lobed nucleus & granulated cytoplasm that stains with both acid & basic dyes.

3. It is often called a “Polymorphonuclar leukocytes (PMN)”.

4. The cells contains primary & secondary granules:

larger, denser granules Peroxidase, Lysozyme,

& Various hydrolytic enzymes.

Smaller. Secondary granules Collagenase, Lactogenase & Lysozyme

4. The cells exhibit a larger “Respiratory Burst”

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4. Mast cells:

1. Mast cells are about 10 to 30m in diameter and they have polymorphous nucleus.

2. The cells are similar to basophilis of the blood, in appearance and function.

3. It play an important role in the development

4. The mast cells are of two types

Mucosal Mast cells

found in the mucosa of the lung and GUT. The cells are dependant on lymphocytes

for differentiation.

Connective tissue Mast cells

Present at the sites of immediate hypersensitivity reactions.

The granules of mast cells release substances

Seratonine, Histamine, Heparin, Leukotrienes, Prostaglandins and Platelet activating factorwww.BiochemDen.in

5. Antigen Presenting Cells:

The immune system contains of three types of antigen presenting cells (APC's).

1.Macrophages

2. B-cells3.Dendritic cells

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MonocytesMacrophages (MΦs)

1. Macrophages are phagocytic cells, derived from the blood Monocytes.

2. Macrophages are the part of the INNATE IMMUNITY.

3. The macrophages are amoeboid cells having bilobed nucleus & predominant cytoplasmic lysosomes.

4. Macrophages like cells serve different functions in different tissues & are named according to their tissue location.

Alveolar Macrophages In Lungs

Histocytes In connective tissues

Kupffer cells In the Liver

Mesangial cells In the Kidney

Microglial cells In the Brain

Osteoclasts In the Bonewww.BiochemDen.in

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