Anatomy and Components of Immune System

2011

Components of Immune system

Immune System-Anatomy

• The bone marrow hemopoietic stem cells are the ultimate origin of :

erythrocytes all leucocytes including the lymphocytes.

• Many lymphocytes pass through the thymus when they become processed by humoral microenvironment prior to release.

• These lymphocytes are now called thymus-derived lymphocytes, T-lymphocytes or T-cells.

• The majority of the bone marrow derived lymphocytes which do not enter or become processed by the thymus are called B-cells.

Formation of B-cells and T cells

Cells of the Immune system

Many cells of the immune system derived from the bone marrow, Hematopoetic stem cell differentiation

Cells of the Immune system

Lymphocytes

• Lymphocytes are mononuclear, non granular.• Found in blood, spleen, lymph node, tonsil.• They are spherical or ovoid in shape.• They arise from pluripotential haemopoietic stem

cells.• They are important in both humoral and cell-mediated

immunity• Types of lymphocytes:

1. B lymphocytes

2. T lymphocytes

3. Null cells

B lymphocytes /B cells

• Mature in bone marrow • Are mononuclear and non granular• Have a large nucleus• Found in blood and lymph• Highly concentrated in lymph nodes and spleen.• Contain immunoglobulin on their surfaces.• Immature B cells changes to mature B cells which

has IgD and IgM.• B-cells produce antibodies brings about humoral

immunity

Protection by B cells

• When bacteria, virus and toxins stimulate B cells,• B cells divide rapidly and forms two types of cells

1. Plasma cells- secrete antibodies in response to specific antigens- Primary response

2. B memory cells• move from blood to lymph • Survive for longer time• respond quickly and effectively during similar

subsequent infection• Produce antibodies - secondary response

T Lymphocytes/ T- cells

• Derived from haemopoietic stem cells of bone marrow• mononuclear, non-granular leucocytes that matures in

thymus• They become functional on exposure to antigen• Brings about cell mediated immunity.• Types of T cells:

1. T helper cells ( TH cells)

2. T suppressor cells T ( TS cells)

3. T cytotoxic cells ( TC cells)

4. T delayed type hypersensitivity cells ( TD cells)

T helper cells ( TH cells)

• Regulator cells• T helper cells get activated by very small quantities of

antigens which cannot activate other cells.• Helper T cells: release interleukin-2 which in turn

triggers the release of other cytokines.

Cytokines: any soluble factor secreted that act as a signal to other lymphoid cells. There are two categories:-

1. Lymphokines: secreted by lymphocytes

2. Monokines: secreted by macrophages

Certain cytokines like interferon and interleukins are secreted by both lymphocytes and macrophages

• Lymphokines increase the response of B cells, T killer cells and T suppressor cells.

• B cells are activated to produce antibodies.• Another type of Lymphokines secreted by

helper cells called macrophage migration inhibition factors which cause the accumulation of macrophages around the antigen and activation of macrophages to perform phagocytosis.

T Suppressor Cells (TS cells)

• Suppress the activity of B cells and other T cells.

• Are the regulatory T cells.• They inhibit antibody production by B cells.• They suppress the function of the T killer and

T helper cells.• Suppressor T cells are responsible for immune

tolerance by limiting the ability of the immune system to attack a person’s own body tissues.

Cytotoxic T cells ( Tc) or T killer cells (Tk)

– recognizes the foreign antigen on the surface of virus infected cells and destroy the cells releasing cytolytic protein.

– Cytotoxic substances are probably lysosomal

enzymes manufactured in the Tc cells.– Cytotoxic T cells (Tc) are lethal to tissue cells

that have been invaded by viruses.– The virus particles entrapped in membranes of

infected cells attract T cells because of viral antigenicity and Tc cells ultimately damage the virus infected tissue cells.

• Also play important role in destroying cancer cells, heart transplant cells or other types of cells that are foreign to the persons own body.

T Delayed Type Hypersensitivity cells (TD)

• Brings macrophages to areas where delayed hypersensitivity reaction occur.

• TD similar to TH cells.• TD secrete primarily macrophage chemotoxin

and macrophage migration inhibition factor.• By secreting these lymphokines the TD cells

are directly involved in the delayed hypersensitivity reaction.

Plasma Cell

–Fully differentiated B cells.–Do not divide and have a half life of about

2-4 days.–Found rarely in plasma of blood but are

found in lymph nodes and spleen.– secretes Antibodies (immunoglobulins)

Null Cells

• Are lymphocytes with cytotoxic properties.• Neither B cells nor T cells but intermediate.• Two kinds:

1. Natural Killer cells and

2. Killer cells

Natural Killer cells

– Have 2 or 3 large granules in the cytoplasm– Have kidney shaped nucleus– Kills cells infected with certain viruses

– Kill the target cells without the aid of antibody and complement - antibody independent.

– Destroy the cancer cells and cells infected with herpes and mumps virus.

– Don’t need antibody– Activated by interferon and interleukin

– Both innate and adaptive

Killer cells ( K cells)

• Are antibody dependent.• Depends on the presence of bound antibody, • thus reaction is termed- antibody-dependent

cell- mediated cytotoxic reaction.• K cells can kill a variety of cells such as tumor

cells, bacteria, viruses, fungi and parasites.

Monocytes/Macrophage

• Are large, mononuclear phagocytic

cells derived from monocyte.• Have large nucleus and contain

a large number of lysosomes• Strongly phagocytic to a wide

variety of particulate materials such as microorganisms, dead cells, effete cells, debris, immune complex.

• Phagocytosis and killing of microorganisms

• Activation of T cells and initiation of

immune response.• Involved in the processing of antigen before

they are presented to the T and B cells.

Macrophages are important secretary cells- secrete substances such as components of complement system, hydrolytic enzymes, toxic forms of oxygen and monokines.

• Monocyte is a young macrophage in blood

Dendritic Cells

• Activation of T cells and initiate adaptive immunity

• Found mainly in lymphoid tissue• Function as antigen presenting cells (APC)• Most potent stimulator of T-cell response

Mast Cells

• Large cells with basophilic granules in the cytoplasm.

• Mast cells are similar to basophils of the blood, in appearance and functions.

• Expulsion of parasites through release of granules.

• Release substances like serotonin, histamine, heparin, platelet activating factors, leukotrines and prostaglandins which brings about inflammatory and allergic reactions.

Neutrophil

• Granulocyte–Cytoplasmic granules

• Polymorphonuclear• Short life span (hours)• Phagocytosis• Very important at “clearing” bacterial

infections• Innate Immunity

Eosinophils• Double Lobed nucleus• Granules are rich in hydrolytic

enzymes.

• Kills Ab-coated parasites through degranulation.

Involved in allergic inflammation

• Orange granules contain toxic compounds

Basophils• Might be “blood Mast cells’• A cell-killing cells• Blue granules contain toxic

and inflammatory compounds.• Important in allergic reactions.• The basophilic granules are believed to contain

heparin, histamine, serotonin, platelet activating factor and other vasoactive amines that may be released at the sire of inflammation or region of immediate hypersensitivity reaction.

Other Blood Cells

• Megakaryocyte–Platelet formation–Wound repair– Involved in immune response, especially in

inflammation.– Involved in hypersensitivity reaction.

• Erythrocyte–Oxygen transport

Task• Differentiate between B cell and T cell

END