Immune response description

This chapter first provides a description of immunity in general and then more specifically, immunity in the mucosal immune system. The immune response of both intestinal and respiratory tracts will be described in detail as these are the two most common portals of targeted vaccine development for mucosal immunity. The chapter will cover the basis of mucosal immunity using plant-based oral vaccines. Strategies for increasing mucosal immunity, such as the use of adjuvants, will also be discussed. Finally, the chapter will cover the precliiucal tests and various cliiucal trials that are taking place with respect to production of human and veterinary therapeutic proteins in plants. 

Immune responses have often been described in terms of humoral and cellular components. The humoral response involves the small circulating B lymphocytes (B cells), the antibodies (immunoglobulins), and proteins of the complement system. The cellular response is mediated by another group of small lymphocytes, the T lymphocytes (T cells). They resemble B cells in appearance but have quite different functions. However, newer knowledge has provided a somewhat different description of the body s defense... 

The innate and adaptive branches of the immune response are both needed for optimal immune function, and the two interact extensively.18,23 The adaptive response s ability to recognize and deal with foreign pathogens likewise involves an incredibly complex interaction between various cellular and chemical (humoral) components.23 48 51 A detailed description of the intricacies of how these components work together is beyond the scope of this chapter. Many aspects of the immune response are still being investigated. An overview of key cellular and humoral elements that mediate acquired immunity is illustrated in Figure 37-1, and these elements are described briefly below. 

We now turn to an anatomical description of lymph nodes. The lymph node is surrounded by a thick, fibrous capsule and is subdivided into compartments by trabeculae. Inside the capsule is the subcapsular or marginal sinus, which forms the entry point of lymphatic fluid into the node, via the afferent vessel. The lymph node cortex, which lies beneath the subcapsular sinus, is the location of the primary and secondary lymphoid follicles. The primary follicles are comprised of B-lymphocytes. An immune response stimulates B-cells to replicate and differentiate, converting the primary follicle into a secondary follicle or germinal center, surrounded by a zone of small lymphocytes. The paracortex surrounds the germinal centers and primary follicles and contains mostly T-lymphocytes. The medulla is composed of medullary cords, consisting of macrophages and plasma cells, and medullary sinuses. The medullary vessels include the arteries and veins, and the afferent and efferent lymphatic vessels, respectively, deliver the lymphatic fluid into and out of the lymph node. 

An important distinction must be made between the humoral response to a pure, capsular polysaccharide, and to the same polysaccharide when it is an integral part of the bacterium. Thus, the immunity received on recovery from infection by encapsulated bacteria, in terms of the polysaccharide antigen, differs from that generated by purposeful immunization with purified capsular-polysaccharide vaccines. Fortunately, with the exception of infants, the polysaccharide vaccines still stimulate protective-antibody levels in humans, despite these differences. In infants, due to the immature nature of their immune systems, these polysaccharide vaccines are of only marginal benefit.7 Some insights into the nature of these different responses in humans can be found in studies on the cellular basis of the immune response to polysaccharides. However, for the purposes of this Chapter, it would be inappropriate to provide a lengthy description of this incompletely understood mechanism in-depth reviews of this burgeoning field of research can be referred to.144-147,162-166... 

An antigen injected into a test animal elicits an immune response by binding to determinant specific receptor sites on two types of small lymphocytes denoted B and T. These receptor sites have been shown to be immunoglobulins integrated into the lymphocyte cell membrane, which accounts for their determinant specificity. A few characteristics of B and T lymphocytes are listed in Table 8-2, but their ontogeny, function, and interactions are immensely more complex than such a casual description... 

Immune responses can be directed toward a new nonself antigen that has become nonspecifically absorbed to a cell membrane. This mechanism is essentially the description of the sensitizing potential of a hapten and is one of the reasons why there is some overlap between hypersensitivity reactions and autoimmune conditions. 

Disease is caused when the number of antigens overcomes the immune response. Marchuk (1983) gave a simple mathematical description of the disease process, calling, for the sake of simplicity, all antigens to be "viruses" and all immune responses to be "antibodies" (Bell, 1971). 

So far, the described phenotypes that led to the identification of viral genes interfering with the immune response are frequently the modulation of MHC class I functions that affect the CTL and NK response of the host. The description of the loss of MHC class I from the cell surface led to the identification of immune-evasive... 

To date, only the mentioned vCKBPs have been studied as potential therapeutic agents. However, a whole set of other vGKBPs from different origins and with different properties and modes of action have been described. Possibly, each of them has evolved to control specific aspects of the activation of the immune response. Therefore, a detailed description of their roles in vivo in their own biological context may help define their potential clinical applications (Table 16.1). Indeed, the examination of the chemokine spectrum bound by each of them in comparison... 

In this section we shall address ourselves to a description of the specific immune responses which have been shown to be under the control of H-linked Ir genes in guinea pigs, mice, rats and rhesus monkeys. 

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