BT302 Immunology Special Gift by Iqbal

Cytokines belong to diverse group of non-antibody proteins which act as mediators between cells. Initially, these proteins were considered as products of immune cells. More importantly, these were also considered to act as mediators for immune cells. Later on, it was also found that these are also produced from non-immune cells and served as mediators too. Cytokines are used as biological response modifier for treatment of various diseases. In general, cytokine is a general term but it can be more specific term which is used according to their cell of origin as follows Monokines These are produced by mononuclear phagocytic cells.

These are produced by activated lymphocytes.

These are the mediators between leucocytes

These are responsible for leucocytes migration and inflammatory process Cytokines usually perform their functions as cascade signaling in the form of a network which is termed as cytokine network. Their functions are for enhancing their effects of other cytokines in an additive or synergistic manner. Moreover, these act for suppressing the effects of other cytokines in an opposing or antagonistic way. Cytokines are not as preformed proteins like antibodies. These are produced by gene transcription as needed because mRNA for cytokines are short lived in nature. Furthermore, the individual cytokine can act on many cells of the host which is termed as pleotropic response of cytokines.

Mechanism of acting of Cytokines

Cytokines act through specific receptors present on various cells. These are considered as redundant in nature. The redundancy of cytokines is due to the nature of cytokine receptors. The complex interaction between host’s cells and cytokines occur through cytokine network. Different cells can respond to same cytokine due to structural similarities among cytokine receptors (Fig.13.1). The cytokine signaling is flexible which can have both protective and damaging effects. Similarly, thes can also influence the synthesis of other cytokines.

Figure 13.1: The structure of various cytokine receptors Cytokines bind to specific receptors with high affinity and respond in following three ways

1. Autocrine

These effect on same cells which secrete the cytokine

2. Paracrine

In this way, the cytokines effect on nearby cells of cytokine secreted cells.

3. Endocrine

Through this way, the cytokines effect on distant cells through circulation.

Categories of Cytokines

Cytokines are categorized on following two basis I. Their source of origin II. Their functions I. Categories based on source cells Followings are the categories of cytokines on the basis of their source of origin i) Monokines As the name indicates, these are produced by mononuclear phagocytic cells for example Interferon gamma and Interleukin (IL-1) from macrophages & Monocytes ii) These are produced by activated lymphocytes for example IL-3, IL-4 & IL-5. iii) These are mediators between leucocytes for example IL-1, IL-10& IL-18. iv) These are responsible for leucocytes migration for example IL-8. II. Based on functions On the basis of functions, cytokines are categorized into following two categoryies a) Cytokines which act for Innate (non-Specific) immune system e.g TNF-α, IL-1, Il-10 etc b) Cytokines which act for Adaptive (Specific) immune system e.g Il-2,IL-4 & IL-5

Cytokines of Innate Immune System

These cytokines which act primarily for innate (non-Specific) immune system. These are as follows