Basic concepts of the immune system

What is immunology?

The study of the molecules ,cells, organs and systems responsible for recognition and disposal of foreign material

Other factors of immunology

-How the body components respond and interact

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the desirable and undesirable consequences of immune interactions

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The ways in which the immune system can be advantageously manipulated to protect against or treat diseases

What are the two main functions of the immune system?

To distinguish between self antigens and non-self antigens and to defend the body against non-self antigens through various mechanisms

What are self antigens?

Endogenous antigens that originate within the body

What are non-self antigens?

Exogenous antigens that originate outside the body

Serology

The study and diagnostic examination of blood serum and other body fluids that can be used for detection of disease and monitoring of therapy through serological laboratory testing

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Blood test done to identify the existence of antibodies and/or antigens associated with a microorganism

What are the two major components of the immune system?

Innate immunity and adaptive immunity

What does the immune system rely on

-Hematopoietic (bone marrow where immune cells are born)

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-Vasculature (blood cells that transport immune cells)

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-Lymphatic (lymph nodes, vessels and organs where immune response are coordinated)

classification of the 3 lines of defenses for immunity

What is innate immunity?

A nonspecific defense system that responds to foreign substances and includes structural defenses, inflammatory processes antimicrobial proteins and phagocytes

What is adaptive immunity?

A specific defense system that responds to specific foreign substances and has the ability to remember antigens

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Evolved mechanism allowing the body to recognize, remember and respond to a specific stimulus (an antigen)

Innate vs. Adaptive Immune System

Antigens

-immunogen

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-molecules that have the ability to initiate adaptive immune responses e.g. components of pathogenic organism

Antibody

Immunoglobulin

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Large Y-shape protein produced by plasma cells that is used by the immune system to identify and neutralize antigens

Primary lymphoid organs

Lymphoid organs where the lymphocytes differentiate and mature from stem cells

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ie:- Thymus (site of T cell development)

.- and fetal liver and postnatal bone marrow (site of B cell development)

What are the main secondary lymphoid organs and tissues?

-Lymph nodes

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- spleen

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-mucosa-associated lymphoid tissue (found in association with mucosal surfaces) MALT

Function of spleen and why people without a spleen are more susceptible to some pathogens

responds to blood-borne antigens ; The spleen helps protect against pathogens that reach the bloodstream

What is the function of lymph nodes?

They protect the body from antigens that come from the skin or internal surfaces and are transported through lymphatic vessels

Which cells arise from the lymphoid progenitor lineage?

B lymphocytes ,T lymphocytes and natural killer cells

What are lymphoid cells?

Multipotent , hematopoietic progenitor cells that give rise to :

B lymphocytes ,T lymphocytes and natural killer cells

What are the three main types of T lymphocytes?

Helper T cells, cytotoxic T cells and regulatory T cells

What is the main role of T lymphocytes?

They play a key role in cell-mediated immunity and manage the immune response

What is the main role of B lymphocytes?

They play a key role in humoral immunity by producing antibodies

What is the role of natural killer cells?

They are involved in innate immunity and provide a rapid response against virus-infected cells

Hematopoiesis

the process of blood cell formation

Summarize hematopoiesis

-Blood cells are derived from the pluripotent stem cell

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--The PPSC eventually gives rise to multipotential hematopoietic stem/progenitor cells that develop along one of two major pathways: myeloid progenitors or lymphoid progenitors

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-pluripotent stem cell gives rise to colony forming units

Myeloid progenitor gives rise to

• -Granulocytes

  • Neutrophils

  • Eosinophils

  • Basophils

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• -Erythroblasts → red blood cells

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• -Megakaryocytes → platelets

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• Monocytes → macrophages after entering tissues

Lymphoid progenitor gives rise to

• -B lymphocytes

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• -T lymphocytes

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• -NK (natural killer) cells

Three pathways of Hematopoiesis

-(Erythropoiesis)The formation of red blood cells

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-(Leukopoiesis)The formation of white blood cells

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-(Thrombopoiesis)The formation of platelets

Further classification of (Leukopoiesis)

-(Granulopoiesis)Formation of neutrophils, eosinophils and basophils

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-(Lymphopoiesis)Formation of B cells and T cells

What are neutrophils and function ?

The most abundant type of circulating phagocyte that rapidly leaves the bloodstream during infection and kills microorganisms

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Release cytokines and chemokines that prolong inflammation

What do primary neutrophil granules contain?

Cationic proteins, defensins, proteolytic enzymes ,lysozyme and myeloperoxidase used to kill bacteria

What do secondary neutrophil granules contain?

Compounds involved in forming toxic oxygen compounds lysozyme and lactoferrin

What is the function of lactoferrin in neutrophils?

It removes essential iron from bacteria

What are eosinophils?

-Granulocytes that play a crucial role in killing parasites and have a limited ability to participate in phagocytosis and regulate other immune cell functions

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-Homeostatic regulator of inflammation suppresses inflammatory reaction to prevent excessive spread of inflammation

How do eosinophils help kill parasites?

Their granules contain toxic

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Cell’s receptors interact with larval stages pf some parasites and damage them through oxidative mechanisms

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-granules also damage antibody coated parasites

What is the role of interleukin-5 in eosinophils?

It is a polypeptide that interacts with eosinophils and causes them to grow and differentiate

Description of Basophils and function

Bi-lobed obscured nucleus in which chromatin filaments connecting them are not visible

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-Release histamine and heparin contributing to inflammatory response to fight invading organisms

What receptors can Basophils bind to

IgE, IgG, complement, and histamine

What do basophil granules contain?

Heparin, chondroitin sulfate, peroxidase, platelet-activating factor and other substances

What are monocytes?

Agranular leukocytes that originate in the bone marrow and circulate in peripheral blood before entering tissues

What do monocytes become after entering tissues and egs ?

Tissue-specific macrophages:

Osteoclasts

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microglia cells

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histiocytes

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Kupffer cells

What are macrophages and importance ?

Highly specialized cells that remove dying or dead cells cellular debris and foreign materials

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important in chronic inflammation, as the early stages of inflammation are dominated by neutrophil granulocytes, which are ingested by macrophages at the end of their lifespan

Two types of macrophages

-Wandering cells:

specialized macrophages ie : pulmonary alveolar macrophages / dust phagocytes function as the first line of defense against inhaled foreign particles / bacteria

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-Fixed cells:

line the endothelium of capillaries and sinuses of organs such as bone marrow and spleen

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In strategic locations such as the lungs ,liver ,neural tissue, bone, spleen and connective tissue

Explain how immunocontent cells are developed (bk)

Where does antigen challenge occur?

In secondary lymphoid tissues such as lymph nodes spleen and other lymphoid tissues

What happens after lymphocytes become activated?

Activated immunocompetent B and T cells recirculate in the blood and lymph

What is immunocompetence?

The ability of mature T or B cells to display receptors on their cell membrane for a specific antigen

What is the significance of the receptors on an individual lymphocyte?

All receptors on one cell are identical and recognize a specific antigen

How are T cells selected in the thymus?

Through positive selection and negative selection

What is positive selection?

The process in which T cells that recognize MHC survive

What is negative selection?

The process in which T cells that react against self-antigens on MHC are eliminated

What happens to most initial T cell precursors during selection?

Most are eliminated and approximately 2 percent survive

What happens to B cells during development?

B cells are sorted in the bone marrow by an incompletely understood process

What is humoral immunity?

Adaptive immunity in which B lymphocytes play the key role by producing antibodies

What is cell-mediated immunity?

Adaptive immunity in which T lymphocytes play the key role

What is the main difference between humoral and cell-mediated immunity?

Humoral immunity is mediated primarily by B lymphocytes and antibodies while cell-mediated immunity is mediated primarily by T lymphocytes

What happens during T cell activation?

An antigen is combined with MHC and displayed on the plasma membrane then the T cell receptor binds to MHC and is stimulated by the associated antigen

What is required in addition to antigen recognition for T cell activation?

A co-stimulator such as cytokines or interleukins

What is the function of a co-stimulator during T cell activation?

It prompts the T cell to form a clone

What happens when a T cell does not receive a co-stimulator?

The T cell becomes tolerant to the antigen in a state called anergy

What is anergy?

A state in which a T cell becomes tolerant to an antigen in the absence of an appropriate co-stimulator

What is the role of helper T cells?

They help manage and regulate the immune response

What is the role of cytotoxic T cells?

They are a type of T lymphocyte involved in cell-mediated immunity

What is the role of regulatory T cells?

They are a type of T lymphocyte involved in regulating the immune response

What is the role of B cells in the immune response?

They produce antibodies and are responsible for humoral immunity

What is the role of T cells in the immune response?

They participate in cell-mediated immunity and manage the immune response

What is the relationship between antigen recognition and lymphocyte activation?

Specific antigen recognition by lymphocyte receptors leads to activation when the appropriate requirements for immune activation are present