Re: If I donate blood often, would I be decreasing my built-up immunities?

Hi Al,
Absolutely no worries about depleting your antibodies because of repeated 
blood donations.  Antibodies, like all proteins in the blood, are 
constantly turning over.  The speed at which this happens determines the 
half-life of the protein.  The half-life of IgG antibodies, which are the 
most abundant in blood, is about three weeks; in three weeks from now, one 
half of your antibodies would be gone if they weren’t being replenished.  
The cells that produce the antibodies are called plasma cells and may live 
a long time.  They will keep replenishing the antibodies that are being 
turned over.  However, it is necessary for some immunity, like to tetanus, 
to get revaccinated every so often to replenish the plasma cells making 
anti-tetanus antibodies.  More information can be found in any Immunology 
textbook, for example:  http://www.whfreeman.com/ku
by/index.htm. Keep on donating!