Large parasites killing

Killing of intracellular bacteria and large parasites in the extracellular fluid... 

KILLING OF INTRACELLULAR BACTERIA AND LARGE PARASITES IN THE EXTRACELLULAR FLUID... 

The significance of large parasites as pathogens in humans is indicated by the evolution of two new cells and one new antibody. These are the eosinophil, the mast cell and IgE (Appendices 17.1 and 17.2). It is the collaboration between these cells and the IgE antibodies that enables the body to kill these parasites. 

Eosinophils, which constitute only 1 to 4% of the total number of white blood cells, are only weak phagocytes. These leukocytes are produced in large numbers in individuals with internal parasitic infections. The eosinophils attach to the parasites and secrete substances that kill them, including ... 

In passively immunized neonatal rats, Tyv-specific antibodies exclude larvae from the epithelium (Appleton et al., 1988), where large numbers of excluded larvae become entrapped in mucus (Carlisle et al., 1991a). Similarly, when immune adult rats are challenged with larvae, many luminal parasites are observed entrapped in mucus (Lee and Ogilvie, 1982 Bell et al, 1984). Larvae are neither injured nor killed by mucus entrapment, which is reversible and is not a requirement for expulsion (Carlisle et al., 1990). Rather, mucus appears to participate in expulsion by temporarily confining larvae to the lumen, thus facilitating their elimination from the intestine by normal physiological processes. 

Th2 cells The Th2 cells secrete cytokines (IL-4, -6 and -10) that stimnlate B-cells. They can cause a class switch from IgG to IgE antibodies. The latter activate eosinophils, which are important in killing parasites that are too large to be phagocytosed. Unfortnnately, they are also involved in allergic reactions (see below). 

One of the reasons there are more types of cells than soluble factors is that they must have the capacity to distinguish between those pathogens that are present in the extracellular fluids (e.g. blood and lymph), those that are present within host cells (e.g. vimses, some bacteria) and those that are too large to be phagocytosed (some parasites e.g. helminths, worms). The mechanisms of killing, therefore, must be sufficiently flexible to deal with all of these pathogens. 

The antigens on these parasites stimulate B-cells to produce IgE antibodies which do two things (i) they coat (opsoifise) the parasite and (ii) they bind to the mast cell via a specific receptor. The parasite is sufficiently large that many eosinophils bind to it, via the IgE antibodies. Many of the eosinophils are so close that they are in direct contact with the plasma membrane of the parasite. The lysosome of the eosinophil can fuse with the plasma membrane and the contents of the lysosome are released in close proximity to the parasite, which is then damaged or killed by proteolytic and other enzymes (Figure 17.34). 

Trichlorfon is mostly used to kill mangold fly larvae it is also very efficient against the dangerous rice weevil, which can destroy whole harvests. Trichlorfon is successfully used in viticulture (to kill grapevine moths) and pomiculture (to kill apple, pear and plum sawflies, apple ermine moths and gooseberry sawflies). Trichlorfon is very efficient in cot-ton-growing (to kill cotton worms). The low toxicity of trichlorfon for warm-blooded animals accounts for its use in veterinary medicine to combat parasites on large animals. 

The modern period of chemotherapy, the treatment of disease by use of chemical substances, began with the work of Paul Fhrlich (1854-1916). It was known at the beginning of the present century that certain organic compounds of arsenic would kill protozoa, parasitic micro-organisms responsible for certain diseases, and Ehrlich set himself the task of synthesizing a large number of arsenic compounds, ill an effort to find one which would be at the same time toxic (poisonous) to protozoa irj the human body and non-toxic to the human host... 

Control Usually controlled by natural enemies (blister beetle larvae, ground beetles, predatory flies, birds, parasitic nematodes, fungal dieases) cultivate fields in fall to kill overwintering eggs aerial sprays of commercial protozoan disease Nosema locmtae) may be effective over large areas but is not useful on a home-garden scale. 

Quinoline compounds and the plants that contain them have historically anchored the antimalarial arsenal, and they remain principal drugs today. Quinine and its diastereomer, quinidine, are quinoline alkaloids which were isolated in 1820 from the bark of the Cinchona tree, by virtue of the traditional South American use of this bark to treat intermittent fevers. Quinine is an effective schizonticide (i.e., it kills the form of the parasite in peripheral blood), but because it also affects mammalian lysosomes, the drug has been associated with significant adverse toxicity (48,50). The development of synthetic derivatives of quinine has resulted in improvement in potency and selectivity over the parent compound. Chloroquine and mefloquine are more potent and less toxic than quinine (49,51), thus, chloroquine had largely replaced quinine in clinical use however, resistance of P. falciparum to chloroquine has been reported... 

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