Host Cell Susceptibility

It has long been known that cells vary greatly in their susceptibility to viral infection, even when no differences can be demonstrated in their surface receptors for virus adsorption. Moreover, the same virus clone can inhibit macromolecular synthesis in one cell type to a greater extent than another, even though virus yields may not differ significantly. For example, Baxt and Bablanian (1976 ) showed that VSV inhibits nucleic acid synthesis in BHK-21 celts more readily than it does in LLC-MK2 cells. Week and Wagner (1978) also reported that MFC-11 mouse myeloma celts were more susceptible to VSV shut-off of cellular RNA synthesis than were BHK-21 or mouse L cells. 

PROTEIN SYNTHESIS INHIBITION BY VESICULAR STOMATITIS VIRUS 

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Silvie O, Greco C, Franetich JF, Dubart-Kupperschmitt A, Hannoun L, van Gemert GJ, Sauerwein RW, Levy S, Boucheix C, Rubinstein E, Mazier D. Expression of human CD81 differently affects host cell susceptibility to malaria sporozoites depending on the Plasmodinm species. Cell Microbiol 2006 8 1134-1146. 

It must not alter virus infectivity or host-cell susceptibility. 

In order to obtain any significant understanding of the nature of viruses and virus replication, it is necessary to be able to quantify the number of virus particles. Virus particles are almost always too small to be seen under the light microscope. Although virus particles can be observed under the electron microscope, the use of this instrument is cumbersome for routine study. In general, viruses are quantified by measuring their effects on the host cells which they infect. It is common to speak of a virus infectious unit, which is the. smallest unit that causes a detectable effect when placed with a susceptible host. By determining the number of infectious units per... 

Attachment (adsorption) of the virion to a susceptible host cell ... 

Many plasmids are known to possess three properties (1) increased resistance to the bactericidal effects of UV and chemical mutagens, (2) increased spontaneous mutagenesis, and (3) increased susceptibility to UV and chemically induced mutagenesis. Some plasmids possess all three properties others may possess just one, for example, increased susceptibility to mutagenesis (review Mortelmans and Dousman, 1986). Often the profile of activity depends on the DNA repair status of the host cell (Pinney, 1980). Plasmid pKMIOl carries DNA repair genes and has been widely used in strains used in bacterial mutagenicity tests. 

As it is the outer surface of the virus particle, whether nucleocapsid or envelope, that first makes contact with the membrane of the host cell, its structure and properties are of vital importance in understanding the process of infection. In general, naked (envelope-free) viruses are resistant and survive well in the outside world they may also be bile-resistant, allowing infection through the alimentary canal. Enveloped viruses are more susceptible to environmental factors such as drying, gastric acidity, and bile. These differences in susceptibility influence the ways in which these viruses can be transmitted. 

In a recent study (54), we showed increased activities of two enzymes of the general phenylpropanoid pathway, PAL and 4-coumarate CoA lig-ase, as well as one enzyme of the specific pathway of lignin biosynthesis, cinnamy 1-alcohol dehydrogenase (CAD), in resistant plants at the time of the hypersensitive host cell death. On the other hand, decreased activities were observed at the same time with susceptible host plants (54). Furthermore, we showed that the well known increase in peroxidase activities, which is strong in resistant and only weak in susceptible plants (55-58), is at least partly due to the increased activity of the lignin biosynthetic pathway (54,59). 

Figure 1. Hypothetical scheme of events leading to race-cultivar specific resistance or susceptibility in the rust system. If the substrate specificity of the fungal cell wall degrading enzymes (e.g., pectinases) is suitable for degradation of a specific host cell wall component (e.g., partly esterified pectin), endogenous suppressors will be produced which prevent the elicitor induced lignification response, thus leading to susceptibility.

Docosanol is not directly virucidal instead, it blocks the entry of the virion into the host cell by inhibiting the fusion of the viral envelope with the host plasma membrane. Because it does not affect viral replication or protein production, it may be less susceptible to the development of resistance than other antiviral drugs. 

The specific interaction of chemicals or radiation with DNA activate cdlular DNA repair processes which appear to play an important role in carcinogenesis. Eukaryotic cells show enhanced repair capacity for repair of viral nucleic add if the host cells are first damaged by chemicals or irradiation. The ihanced susceptibility to cancer of patients with defective repair systems, such as those with xeroderma pigmentosum, suggests that intact repair mechanisms are protective... 

Neun, D.J., Penn, A. Snyder, C.A. (1992) Evidence for strain-specific differences in benzene toxicity as a function of host target cell susceptibility. Arch. Toxicol., 66, 11-17... 

Cancer cells don t grow any faster than normal cells but they continue to divide when normal cells would not. For this reason, a cancer can grow rapidly and its demands for nutrients can literally starve the host. Cancer tends to weaken the immune system, making the host more susceptible to infections. In addition, cancers often interfere directly with the functioning of various organs and may cause death in this way. 

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