Role of cytokines in the immune system
- Iain B McInnes, FRCP, PhD
Iain B McInnes, FRCP, PhD
- Professor of Medicine
- University of Glasgow
The immune system is a complex network designed to protect the host from both external (such as bacteria and viruses) and internal threats (such as malignant transformation). Cytokines are important mediators of immune responses that allow integration of the behavior of cells in time and geographical location as immune responses are generated.
Cytokine-directed treatments are being developed by the pharmaceutical and biotechnology industry as therapeutic agents for a number of autoimmune diseases. Clinicians using these treatments should understand the role of cytokines in the normal immune system, a topic that is reviewed here. The role of cytokines in the pathogenesis and treatment of rheumatic disorders is discussed separately. (See "Role of cytokines in rheumatic diseases" and "Cytokine networks in rheumatic diseases: Implications for therapy".)
OVERVIEW OF IMMUNE RESPONSES
The immune system is organized into innate and adaptive immune responses, with adaptive immunity further subdivided into two branches, humoral and cell-mediated immunity. (See "An overview of the innate immune system" and "The humoral immune response" and "The adaptive cellular immune response".)
Innate immunity is immediate and rapid. Innate defense mechanisms include neutrophils and macrophages, which, among other functions, can ingest and destroy pathogens. While often effective in protecting the host, innate immunity is associated with damage to host tissue in the context of providing defense. It is also amnestic in that the inciting agent is not specifically recognized by a unique structure and there is no creation of a memory to that agent such that future responses are more efficient.
Adaptive immunity is slower in its response to threats, particularly upon first exposure to that organism (naïve responses are slower than memory responses). However, it provides two main features that innate immunity lacks: specific antigen recognition and memory that allows rapid recall of original antigen exposure. Host defense is generally provided in two major arms of the adaptive response:
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- OVERVIEW OF IMMUNE RESPONSES
- CYTOKINE INTERACTIONS
- CYTOKINE MEASUREMENT
- Soluble cytokine assays
- - Biologic assay
- - Immunoassay
- Localizing cytokines in tissues
- CYTOKINES IN NORMAL IMMUNITY
- Antigen presentation
- T cell subsets
- - Th1
- - Th2
- - Th17
- - Th0
- - Regulatory T cells
- Amplification effects of cytokines
- Cellular migration
- Negative feedback
- Effects beyond the immune system