Innate immune system monocytes/macrophages

The components of the immunosurveillance are the innate immune system, consisting of monocytes, macrophages, dendritic cells (DC), natural killer (NK) and NKT cells, and the adaptive immune system, represented by DC, B-cells, and T cells (Fig. 1). 

The major cell types of the innate immune system include monocytes (blood precursor cells of antigen-presenting cells), antigen-presenting cells (macrophages, dendritic cells), granulocytes (neutrophil, eosinophils, basophils), mast cells and natural killer cells. All these cells depend on chemokines for migration and, additionally, they are an important source for chemokines. 

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. 

Non-specific cellular immunity All other immune cell types such as granulocytes, various cells of the mononuclear phagocytosis system (macrophages/ monocytes, dendritic cells) or natural killer cells form part of the (less specialized) innate immunity. 

The immune system is divided into two defense mechanisms nonspecific, or innate, and specific, or adaptive, mechanisms fhat recognize and respond to foreign substances. Some of the important cellular components of nonspecific and specific immunity are described in Table 9.2. The nonspecific immune sysfem is the first line of defense againsf infectious organisms. Its cellular components are the phagocytic cells such as the monocytes, macrophages, and polymorphic neutrophils (PMNs). 

Inflammation is a complex and well-coordinated response of the innate and adaptive immune system following infection or injury. This process is characterized by a vascular response and recruitment of circulating leukocytes, defined initially by polymorphonuclear granulocytes followed by monocytes, which differentiate locally into macrophages [47]. 

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