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LACTOGENIC IMMUNITY IN THE SOW: A PRACTICAL APPROACH
HUMORAL COMPONENT Proteins and biochemical mediators which have various functions are included in this class (Table 1). The complement system is one of these groups of proteins, formed from a wide variety of proteins that are found in high levels in the plasma. The various components of the complement system are a set of plasma molecules that interact in a certain order to perform their role in the body’s defence. Their function is to boost the inflammatory response, enable phagocytosis, and organise cellular lysis. Other proteins involved in this response are the acute phase proteins. These include some very important proteins, such as the pentraxin family, which includes C-reactive protein, serum amyloid protein, haptoglobin, and mannose-binding lectin (MBL). Their functions are varied, but they all bind and activate complement proteins, enabling opsonisation. Opsonisation can proceed in two ways: antibody opsonisation is the process by which a pathogen is marked with an antibody for ingestion and destruction by a phagocyte. The cell can also be destroyed by a process called antibody-dependent cytotoxicity, where the
pathogen does not have to be phagocytosed to be destroyed. The last, large family of proteins activated in the innate immune response is the cytokines. These proteins regulate the function of the cells that produce them, or the function of other types of cell. They are responsible for intercellular communication, and they activate specific membrane receptors. They also regulate cell proliferation and differentiation, chemotaxis and growth, and they modulate immunoglobulin secretion. Immunoglobulins are mainly produced by activated lymphocytes and macrophages, although they can also be secreted by other cells. Their main activity is to regulate inflammation. Some cytokines are pro-inflammatory (TNF-α, IL-1), and others are anti-inflammatory (IL-2, IL-4). One very important group of cytokines are type I interferons (IFN-alpha, beta, omega, epsilon, and kappa) which are produced naturally by most animals’ immune systems in response to external agents. Interferon production is triggered by other cytokines, such as IL-1, IL-2 and TNF-α, which are synthesised when a virus is detected in the body.
In conclusion, the humoral components of the innate immune system can be summarised as complement system proteins, acute phase proteins, and cytokines (Table 1). The nonspecific defence mechanisms provide a good system of protection, but they are often insufficient to defend the body effectively. Fortunately, the body also has a specific immune response, termed adaptive or acquired (Fig. 2).
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