Immune system effectors

A mechanism of cell-mediated immunity whereby an effector cell of the immune system actively lyses a target cell that has been bound by specific antibodies. The typical ADCC involves activation of natural killer (NR) cells and is dependent on the recognition of... 

Antigen-presenting cells (APCs) are cells of the immune system that are able to process and present foreign antigens to effector cells. The antigen is presented in the context of an MHC-I or MHC-II molecule on APCs in the presence of so-called costimulatory molecules to activate the effector cells. 

Humoral immunity depends on soluble, noncellular effector mechanisms of the immune system. These include defensins and complement components (proteins of the innate immune system) and antibodies (products of the adaptive immune system). They are capable of reacting with foreign substances (e.g., bacteria and viruses) to produce detoxification and elimination. 

While cells of the innate immune system can combat invading microbes autonomously, their effector mechanisms are also used and greatly enforced by the... 

Parallel to orchestrating acute inflammatory processes by providing an optimal milieu of cytokines, mediators, and adhesion molecules in order to recruit and activate effector cells to the site of infection, dendritic cells also setve as professional antigen-presenting cells for cells of the adaptive immune system ( antigen presentation ... 

Immunomodulators are a group of mostly stimulatory effectors which act on cells of the immune system (e.g. cytokines, interferons). 

The key end result of TLR signalling is the induction of cytokines. Cytokines are proteins produced during an immune response that allow the maturation, activation and differentiation of effector cells in the immune system. The activation of NFkB and AP-1 by the MyD88 and the TREF dependent pathways leads to the production of proinflammatory cytokines such as IL-6, TNF-a and various chemokines. This pathway can also activate IRF-7 via TLR-7and TLR-9 allowing Type-I interferons to be produced. 

The main site of the mucosal immune system in the gut is referred to as gut-associated lymphoid tissue (GALT), which can be divided into inductive and effector sites. In the small intestine, the inductive sites are in the Peyer s patches, which consist of large lymphoid follicles in the terminal small intestine. The contact with external antibodies triggers a series of cascade events in the body based on immune response (Brandtzaeg et al., 1999). 

Molecular markers of microglial cells. In the past 10-15 years there has been a veritable explosion of activity in the field of microglial cell biology with the realization that this cell type is capable of functioning as a highly efficient accessory and effector cell of the immune system. 

Lymphocytes, the effector cells of the acquired immune system, include morphologically indistinguishable T and B cells, the former divided into CD4+ T helper cells and CD8+ cytotoxic T cells. Since the functions of those cell subsets differ so drastically, it became important to develop tools to distinguish them from each other. Efforts to identify cell subsets according to their expression of different surface antigens have been successful, including various Cluster of Determination (CD) markers (Table 23.1). In addition, cross-reactive monoclonal antibodies, and subsequently developed species-specific polyclonal and monoclonal antibodies towards the major histocompatibility complex (MHC) have been used to label cells in circulation and in tissue sections (Table 23.1). 

Although closely related, monocytes/macrophages (MO) possess features that are distinct from DCs. Due to their limited expression of T-cell costimulatory molecules, MO are not able to prime T cells de novo, but rather stimulate effector/memory T cells by the secretion of cytokines, which support T-cell proliferation. As DCs, MO differentiate from myeloid precursors and form a heterogeneous population of antigen-presenting cells (APCs) that link the innate and adaptive immune systems. However, their ability to interact with T cells via MHC class II TCR interaction(s) as well as engagement of T-cell costimulatory receptors on their surface, makes close contact between MO and Tregs likely to occur in vivo. 

In conclusion, the mutual interaction of Tregs and APCs enables Tregs to sustain their immunosuppressive function(s), which may be crucial for the maintenance of peripheral tolerance in healthy individuals. Since MO and DCs bridge the innate and the acquired immune system, this crosstalk with MO and DCs permits Tregs to gain influence on the iimate immune system. Furthermore, the impact on APCs offers Tregs to expand their suppression beyond the mere interaction with effector T cells. 

The innate and the adaptive arms of the immune systems of higher organisms are bridged by a complex set of cellular and molecular mediators. The immunomodulatory activities of host defense peptides, such as the direct chemotactic activity, cytokine and chemokine induction, and the stimulation of differentiation and activation of effector cells, may contribute to this process. Host defense peptides may also influence the polarization of adaptive immune response, for example, through their effects on cytokine production. ... 

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