Defensive mechanism

Phytoalexins are low molecular weight compounds produced in plants as a defense mechanism against microorganisms. They do, however, exhibit toxicity to humans and other animals in addition to microbes (30). Coumarins, glycoalkaloids, isocoumarins, isoflavonoids, linear furanocoumarins, stilbenes, and terpenes aU. fall into the category of phytoalexins (31). Because phytoalexins are natural components of plants, and because their concentration may increase as a response to production and management stimuli, it is useful to recogni2e the possible effects of phytoalexins in the human diet. 

Formaldehyde is classified as a probable human carcinogen by the International Agency for Research on Cancer (lARC) and as a suspected human carcinogen by the American Conference of Governmental Industrial Hygienists (ACGIH). This is based on limited human evidence and on sufficient evidence in experimental animals (136). Lifetime inhalation studies with rodents have shown nasal cancer at formaldehyde concentrations that overwhelmed cellular defense mechanisms, ie, 6 to 15 ppm. No nasal cancer was seen at 2 ppm or lower levels (137). 

This wide range of pharmacokinetic properties, along with thek ease of administration, broad spectmm antimicrobial activity, and noninterference with host-defense mechanisms is responsible for thek widespread use five decades after thek discovery. 

Skunks excrete 1-butanethiol and 2-methyl-1-butanethiol [1878-18-8] as a natural defense mechanism (12). Methanethiol is found in cheese, milk, coffee, and oysters (13—16). It is also found in the kuttin fmit, which is endemic to Southeast Asia. 

Extractives and Ash. The amount of extractives in wood varies from 5 to 20% by weight and includes a wide variety of organic chemicals (11). Many of these function as intermediates in tree metaboUsm as energy reserves or participate in the tree s defense mechanism against microbiological attack. The extractives contribute to wood properties such as color, odor, and decay resistance. 

The immune system in vertebrates provides a defense mechanism against foreign parasites such as viruses and bacteria. Three main properties are essential to its successful operation specific recognition of foreign molecules, the ability to destroy the foreign parasite, and a memory mechanism that allows a more rapid response to a second infection by the same microorganism. 

Disruption of these defense mechanisms can lead to bacterial colonization or viral infection. Mucus temperature is important in controlling respiratory infections because decreasing below central body core temperature not only impairs ciliary movement,hut also enhances viral replication,- greatly increasing the likelihood of respiratory infection. Drying of airway mucus also increases the possibility of respiratory infection by reducing mucus thickness and impairing mucociliary clearance, i- i--... 

Widdicombe, J, G. (1977). Defense mechanisms of the respiratory tract and lungs. In International Review of Physiology Volume 14. Repiratory Physiology U (J. G. Widdicombe, Ed.), pp. 291-316. University Park Press, Baltimore. 

Proctor, D. E, Andersen, E, and Lundqvist, G. R. (1977b), Nasal mucociliary funerion in humans, Part 1. In Respiratory Defense Mechanisms pp. 427- 52. Marcel Dekkcr, New York. 

Airway defense mechanisms Group of physical, physiological, and immu-... 

Usually fairly high concentrations of such a drug are needed for effective control of an infection because the inhibitor (the false substrate) should occupy as many active centers as possible, and also because the natural substrate will probably have a greater affinity for the enzyme. Thus the equilibrium must be influenced and, by using a high concentration of the false substrate, the false substrate-enzyme complex can be made to predominate. The bacteria, deprived of a normal metabolic process, cannot grow and multiply. Now the body s defense mechanisms can take over and destroy them. 

Rees, J.-F., et al. (1998). The origins of marine bioluminescence turning oxygen defense mechanism into deep-sea communication tools. J. Exp. Biol. 201 1211-1221. 

Extracts from 152 plant species, representing 46 different families, were screened for effects on tobacco mosaic virus (TMV) replication in cucumber cotyledons. Twenty species have shown enough activity to warrant further study. Several members of the Caprifoliaceae family increased virus replication. An extract of Lonicera involucrata enlarged the virus lesions in local lesion hosts and produced a thirty fold increase in virus titer, but had no effect on virus replication in systemic hosts. The active material appears to affect the virus defense mechanism of local lesion hosts. An extract of common geranium is an active virus inhibitor. It inactivates TMV and TMV-RNA (ribonucleic acid) in vitro by forming non-infectious complexes. In vivo, it also inhibited starch lesion formation in cucumber cotyledons incited by TMV infection. 

Therefore, in the cucumber-TMV system, tannic acid treatment had no effect on the establishment of infection it merely suppressed the expression of starch lesions and at the same time interfered with the defense mechanism of the host, permitting systemic spread of the virus. 

In both cases, a seeming virus stimulator (twinberry extract) and a virus inhibitor (tannic acid) operated in a more or less similar way in the cucumber-TMV system. They both affect the host defense mechanism against virus infection. The active component in twin-berry extract exhibits a mild and temporary interference, thus permitting virus to make further rounds of gain (ringlike patterns) while tannic acid produces a strong and permanent interference. 

Type II, III, and IV allergic reactions are variants of physiologic defense mechanisms only relevant in special situations, which follow a common pathologic pattern. In general, treatment of these forms require antiinflammatory ( inflammation) or immunosuppressive strategies ( immunosuppression). Therefore, only therapy of Type I reactions will be described here. 

Knowles MR, Boucher RC (2002) Mucus clearance as a primary innate defense mechanism for mammalian airways. J Clin Invest 109 571—577... 

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