Re: biological viruses

Charlie,

Good question.  It turns out that not only viruses but also bacteria and 

other organisms which invade your body are often quite picky about which cell

they first interact with and enter.  The easiest answer to give is that 

each cell type, whether it is a skin cell or a white blood cell has a set 

of molecules on its outer surface which are found only on that cell.  It is 

these molecules (called receptors) that are recognized by the invader and 

allow it to attach to and enter that cell.

HIV for example recognizes a protein called "CD4" on T-lymphocytes (part

of the white blood cell family) while the Varicella zoster virus (chicken

pox virus) appears to recognize a protein/sugar molecule (called a 

proteoglycan) on skin cells.

It's also interesting that some organisms (such as a the parasite Toxoplasma)

appear to invade every type of human cell known, so whatever its recognizing

must be found on all cell types.

Thanks for your question Charlie

Michael Crawford



Oh yeah, I almost forgot.  Here's some information on HIV

that talks a little about the virus, CD4 interaction, etc. 

Bye