Proteins of the complement system

Immunoglobulins play a key role in the defense mechanisms of the body, as do proteins of the complement system. Some of the principal features of these proteins are described. 

When neutrophils encounter bacteria, possibly coated with opsonin proteins of the complement system, the invaders are engulfed by the phagocytes and taken into the cells by endocytosis. A small part of the neutrophil membrane is used to create a phagosome - that is, a vacuole enclosing the bacterial cells. Within a matter of a few... 

The table also lists important globulins in blood plasma, with their mass and function. The a- and p-globulins are involved in the transport of lipids (lipoproteins see p. 278), hormones, vitamins, and metal ions. In addition, they provide coagulation factors, protease inhibitors, and the proteins of the complement system (see p. 298). Soluble antibodies (immunoglobulins see p. 300) make up the y-globulin fraction. 

Manderson, G. A., Martin, M., Onnerfjord, P., Saxne, T., Schmidtchen, A., Mollnes, T. E., Heinegard, D., and Blom, A. M. (2009). Interactions of histidine-rich glycoprotein with immunoglobulins and proteins of the complement system. Mol. Immunol. 46, 3388-3398. 

Of the particulate stimuli certain ones are far more active when they are coated with proteins from serum (opsonized) than when they are not. However, others like latex beads elicit formation of Oj" by PMNs without opsonization DeChatelet et al. found that the production of O by PMNs from man and rabbit was stimulated by opsonized but not unopsonized zymosan (fragments of yeast cell walls). Bacteria alone were found to stimulate the formation of O but in the presence of serum bacteria stimulated the formation of O7 three fold However, the stimulatory effect of bacteria appeared to be caused by changes which the bacteria produced by an interaction with constitutents of serum, because serum itself after exposure to the bacteria stimulated production of O by PMNs. The active component from serum was heat sensitive (100°) and not sedimentable at 105,000 g. Whether this material was derived from the components of serum or from the bacteria is not clear but may have been a protein of the complement system. 

Immunoglobulins, oq-trypsin inhibitor and a2-macroglobulin,k ten or more blood clotting factors and proteins of the complement system all have protective functions that are discussed elsewhere in this book. Hormones, many of them proteins, are present in the blood as they are carried to their target tissues. Many serum proteins have unknown or poorly understood functions. Among these are the acute phase proteins, whose concentrations rise in response to inflammation or other injury. 

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... 

Several other types of covalent crosslinks, mostly derived from lysine or 5-hydroxylysine residues (the latter being formed by post-translational modification), are found in collagen and elastin. A few examples are given (5.2-5.7) A6 7-dehy-drolysinonorleucine (5.2), lysinonorleucine (5.3), dehydrohydroxylysinonorleucine (5.4), lysino-5-ketonorleucine (5.5), desmosine (5.6) and isodesmosine (5.7). An intrachain thiol ester loop is present in a2-macroglobulin and proteins of the complement system and consists of a fifteen-membered ring derived from cysteine and glutamic acid (5.8). 

Proteins of the Complement System Alternative, Classical, Lectin, and Membrane Attack Pathways and Complement Regulating Proteins... 

As we have seen in Chapter 4, the immune system comprises the ancient, non-specific, innate immune system and the more recently evolved specific, adaptive immune system. The ancient innate immune system is vital both for providing an initial rapid response to infection, and also in activating the adaptive system.8 A crucial part of the early innate immune system response is provided by two proteins of the complement system called C3b and C4b. These proteins are vital in the recognition and destruction of invading microorganisms. 

The interaction between the parenteral fat emulsicHis and the MPS. to which the RES belongs, is of crucial importance (150). It consists of circulating hlood monocytes and macrophages which are in the tissues (e.g., Kupffer ceils of the liver) or in the endothelial of the blood capillaries. Their job is to remove substances from the btxly that have been recognized as foreign to it. By sorption of opsonines and proteins of the complement system the fat droplets are marked as foreign and so they are phagocytized by the cells of the RES. 

Alternative pathway One of the sequences of reactions in non-specific host responses by which proteins of the complement system are activated. 

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