What makes influenza a respiratory virus?

[ryan at mbcf.stjude.org]

In article <5uy8dHK.aguldo at delphi.com>, bogleb <aguldo at delphi.com> writes:
> 	Specifically, can anyone tell me (preferably by email, but not
> mandatory) which viral protein imparts "respiratoriness" to influenza
> virus?  Thanks & allocades in advance. . . .
>  
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> Bob R. Bogle, MT(ASCP),CLS(NCA)		Voice:   (520) 694-6107
> Dept. Clinical Pathology		E-mail:  aguldo at delphi.com
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Hi Bob,

this question has several answers. A couple of them are:

1) the hemagglutinin glycoprotein (attaches virus to target cell) must undergo
proteolytic cleavage to be biochemically active. Proteases that can do the job
are found in respiratory tissues (and elsewhere). Concurrent bacterial
infections can also increase the amount of such proteases on respiratory tissue
surfaces. 

2) influenza isn't just a respiratory virus. The nastier pathogenic strains (at
least some avian strains) can spread through virtually all body tissues:
kidney, brain, whatever. But how do you catch these infections? It's very hard
to catch an infection in the brain, since there's no convenient route of direct
entry. In contrast, the respiratory system constantly samples the environment 
and pulls in anything present in aerosols/dust particles/etc. In short, the 
respiratory system is easy to get at. 

Some strains are cleared by the immune response without getting much beyond
respiratory tissues. Some strains spread more rapidly beyond these sites, due
to more rapid virus replication and to an easier-to-cleave hemagglutinin. 

Among other things.

Cheers, Kevin.
-- 
--
       	==========================================
	Kevin W. Ryan
	Department of Virology & Molecular Biology
	St. Jude Children's Research Hospital
	Memphis, Tennessee 38101-0318, U.S.A.
	
	phone: (901) 522-0411
	fax:   (901) 523-2622
	Internet: ryan at mbcf.stjude.org
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