Definition

Cytokines are chemical substances which serve as messengers, mediating interaction and communication between the various cells of immune system.

Major Classes of Cytokines

Present nomenclature of cytokines includes all the com pounds that were known earlier by various names, such as:

* Lymphokines—produced by lymphocytes

* Monokines—produced by monocytes and macrophages

* Interleukins—produced by WBCs and acting on the same or different WBCs

*  Chemokines—involved in chemotaxis and other leukocyte behavior.

Properties of Cytokines

Cytokines are comparable to growth factors and hormones in many ways such as all of them act at very low concentration (picomoles) and through specific receptors. However, there are some differences also.

* Growth factors are produced constitutively while cytokines are inducible, i.e. produced only after the activation of their cells of origin

* Hormones have mostly endocrine effects; whereas cytokines have broad range of effects, which include (Fig. 1):

- Autocrine effect—that acts on the same cell

- Paracrine effect—that acts on the adjacent cell

- Endocrine effect—that acts on a cell present at a distant site.

* Unlike hormones and growth factors which work mostly independently, cytokines can work together and there are various types of interactions occurring between cytokines:

- Pleiotropy and redundancy effect: Pleiotropy refers to same cytokine having different actions on different target cells, whereas redundancy implies to different cytokines producing the same effect on the same target cell (Fig. 2)

- Synergy and antagonism effect: Two cytokines may augment each other’s action producing a larger effect (synergism) or may oppose each other’s action (antagonism)

- Cascade effect: It refers to a series of effects mediated by different cytokines. One cytokine acts on a target cell to produce another cytokine which in turn acts on another target cell and so on.

Fig1. Action of cytokines on target cell.

Fig2. Pleiotropy and redundancy effect of cytokines.

Structure of Cytokines

Cytokines are glycoproteins with molecular weight less than 30 kDa. Most cytokines display high degree of α-helix structure but no β-structure. Cytokines characterized so far belong to one of the four groups—(1) the hematopoietin family, (2) the interferon family, (3) the chemokine family, or (4) the tumor necrosis factor family; each interacting with a separate class of cytokine receptors present on target cell surface.

Functions of Important Cytokines

Though cytokines are secreted by a wide variety of cells, the major producers are TH cells and macrophages. Cytokines produce a range of overlapping functions on the target cells/tissues, which can be broadly categorized into two groups:

 1. Promote development of cellular and humoral responses of adaptive immunity:

- Interferon-γ

- Cytokines such as IL-2, IL-4, IL-5.

2. Cytokines promote various responses of innate immunity:

- Induction of inflammatory responses—by IL-1, IL-8, TNF-α

- Regulation of hematopoiesis—by colony-stimulating factors, IL1, IL-3, IL-7, IL-9, IL-11, etc.

- Antiviral activity—By interferon- α and β

- Antitumor activity—By TNF- α and β

- Pyrogenic activity—By TNF- α, IL-1 and IL-6.

 The functions of individual cytokines are summarized in Table 1.

Table1. Sources and functions of cytokines.

Table1. Sources and functions of cytokines.

Cytokines and Diseases

 Pathogenesis of many diseases is characterized by increased expression of cytokines or their receptors. Common examples include the following:

- Septic shock due to gram-negative bacteria, such as Escherichia coli or Neisseria meningitidis is mediated by the endotoxins released by bacteria that stimulate macrophages to produce IL-1 and TNF-α

- Toxic shock syndrome is caused by the toxin released from Staphylococcus aureus, which activates T cells nonspecifically leading to massive cytokine release and that in turn activates macrophages to release large quantities of IL-1 and TNF-α

- Cancers: Several malignancies have been associated with ↑IL-6, e.g. cervical cancer, bladder cancer, etc.

- Chaga’s disease is caused by a parasite named Trypanosoma cruzi which is shown to inhibit the IL 2α receptor, thus blocking the IL-2 action → leading to inhibition of T_H1 activity → immunosuppression

- Cytokine storm (see highlighted box).

cytokines used in Therapy

 Cytokines offer great promise for the treatment of a number of diseases. Many strategies have been followed to create a cytokine or anticytokine state in the body depending on the need. The strategies are:

* Use of cytokines (e.g. interferons) as drug:

- Interferon-α is used for the treatment of hepatitis B, hepatitis C, hairy cell leukemia, multiple myeloma and chronic myeloid leukemia (CML)

- Interferon-β is used for the treatment of multiple sclerosis

- Interferon-γ is used for the treatment of chronic granulomatous disease.

* Cytokine-toxin conjugates are used to destroy the target cells; here the cytokines help in binding to the target cells so that the toxin can act on them.

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اخبار العتبة العباسية المقدسة

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العتبة العباسية المقدسة تختتم فعاليات البرنامج المركزي الأسبوعي لمنتسبيها

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ما السر وراء مشية إيلون ماسك الغريبة والسريعة ؟

المزيد

مواضيع ذات صلة

Antigen presentation

Structure of MHC Molecule

MHC Genes and Their Products

Macrophage

B Lymphocytes

T Lymphocytes

Immunologic Manifestations of Infectious Mononucleosis

Peripheral Lymphoid Organs

Central Lymphoid Organs

Effector Functions of Complement

Complement Pathways

Mechanisms of innate immunity