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Wednesday, December 28, 2011

The immune system

I’m working up to a reader request of the how’s, why’s, and when’s of the bone, tendon, and muscle conditioning.  That series is going to be rather involved, so before diving into “why bone is cool and what that means to you as the endurance rider”, I wanted to share an equally cool, but much less involved concept. 

The Youngen’s
I’ve just been informed by my boyfriend that the above is not a word, and therefore I can “fake” the spelling.  I think I disagree, but as looking up a dialect spelling in “Where the Red Fern Grows” may be overkill for a Wednesday morning topic about immunity, I’ll let it go for now. 

I’m not sure what you’all (pretty sure that Matt would think that isn’t a word either, but you and I know better) thought was the basis of vaccinating puppies and young animals multiple times, and their vulnerability to infection, but I thought it went something like this:

-puppies (and other young animals) are always susceptible to infection until they get their full set of vaccines because they have immature immune systems that can’t respond to vaccination, so the immune system needs to be stimulated over and over.  The time period is important because the immune system responds the most efficiently during the period early in puppy development. 

Sort of a “young animals are inherently broken and therefore you throw stuff at them a couple of times randomly and hope for the best” hypothesis. 

Because all my readers are brilliant, I’m sure you immediately see the fallacies of this hypothesis.

Turns out that the real mechanisms is a tad more sophisticated than that.  Imagine that. 

In my difference I’ve NEVER had an anatomy or physiology class that addressed immunity, and thought that the spleen was a vestigial organ with no apparent function. 

Yeah.  I may have learned a thing or two in my immunity block. 

Here’s the real story:

There’s all sorts of variations on the theme, but we can safely assume for the discussion here that newborn animals (mammals, such as dogs) have a bunch of antibodies floating around in their system from their mom.  These antibodies protect them from disease.  These acquired antibodies start to wear off eventually and the little pup has to manufacture it’s own.  This is where vaccination comes in - to stimulate the immune system to manufacture protection against certain diseases. 

Why don’t we vaccinate at birth?  Because, those acquired antibodies from the mom prevent the vaccine from working - vaccinations are only effective when the mom-antibodies start to go away.  This why some vaccines are given to the mom at specific times during gestation - the mom will give protection to the youngster through her antibodies.  However, you can’t “make up” for not giving the mom the right vaccines by giving them to the youngster at birth, because the vaccine won’t work!   In summary, you start vaccinating when the the acquired antibodies are going away, and the pup is starting to produce it’s own, which in dogs is about 6 weeks of age. 

The time between the mom antibodies going away, and the pup’s antibodies being produced is an especially vulnerable time for the puppy getting sick, because it’s literally building it’s immune system while the immune system that used to protect it is going away.  This is why it’s important to protect your puppy from unknown dogs and public places - it has a unique vulnerability at this time (which unfortunately also coincides with the socialization period). 

Vaccines try to bridge that dip in the immune system.  We start vaccinating BEFORE the mom antibodies totally go away - which means those early vaccines aren’t very effective.  It’s a desperate effort to give the pup some protection against a disease that could kill them so they aren’t totally unprotected.  Then, we re-vaccinate several times over the next couple of months, each vaccine being more and more effective as the concentration of mom-antibodies are less and less and the pup’s own immune system can respond to the vaccine more and more. 

This same concept explains why dogs with an unknown vaccination history don’t go through the same protocol as puppies.  They have a fully functional immune system, and while we may give a vaccine several times to make sure that the immune system is properly stimulated, we aren’t working with an immune system that is actively rejecting the vaccine. 

Large breed dogs develop slower - which can explain why it’s often recommended to give large breed puppies an extra series or two of their puppy boosters - That “gap” between the loss of the mom’s antibodies, and the development of their own may be bigger, requiring additional vaccines to both “bridge” that gap and to make sure that final vaccine isn’t given too early, before it’s really effective. 

Of course, the information is simplified, as I’m totally ignoring the facts about how 2 or 3 stimulations of the adaptive immune system (which is the immune system primarily stimulated by vaccines) is far more effective than just one exposure etc, but this is the basic concept of “why” behind the “how” young animals are vaccinated.

Here’s some graphical representations of all this from “Veterinary Immunology: An introduction” by Tizard