the immune system:
the body's not-so-simple defenses
Dr. Tom Beckett on the immune system and immune stimulators

As noted earlier, E. Equi (Anaplasma phagocytophilum) has a protein that sits on the bacteria's outer membrane surface. When the bacteria, through tick bites, transfers to (a dog), the bacteria chooses the protein variation needed to stay hidden from that particular host. Lyme disease (Borellia burgdorferi) also has some very effective strategies for evading the host's immune system. How do they manage this? Shouldn't a normal, healthy immune system be able to handle these invaders?

While there is value in thinking about immune functioning in the holistic manner, it is also necessary to remember the immune system is a highly complex and diverse system with many, many parts, mechanisms and functions, not one single, simple, monolithic entity.

Sometimes 99% of the immune functions are quite adequate but the 1% that is puny results in a serious problem.

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We need to recognize a distinction between 'exposure without infection' and the more general case of "exposure of any sort."

In this context "exposure without infection" implies that the animal had an encounter with the type of organism under consideration, but those organisms failed to establish a population in the animal.

Animals have an innate immune system (aka the 'non-specific immune system') that has a number of resources for defeating/destroying any micro-organisms that threaten to invade the animal.

In some (perhaps many??) instances the TBD organisms involved in an encounter may be few in number or not robust for some reason and/or the dog's innate immune defenses are in top-notch shape, with the result that the organisms are wiped out by the innate immune system before they are able to establish a 'resident' population. Thus, an 'exposure without infection'.

If the micro-organisms are able to establish a population in the animal, that animal is 'infected'. If the infecting organism leads to signs/symptoms/pathology, the animal then can be said to be 'diseased'.

Animals also have an adaptive immune system. A major feature of this branch of the immune system is that it has cells which produce *antibodies* to the *antigens* from micro-organisms that the immune cells have encountered. A transient encounter of the *exposure-without-infection* type may be enough to trigger antibody production. Normally an infection will trigger antibody production--whether producing disease or not. Antibodies are normally produced when disease is present - provided there has been time post-infection (usually ~2-3 weeks) for the antibody-producing cells to commence production. The adaptive immune system is big on 'memory' features, so once production of specific antibodies is started, it tends to continue long-term.

So, as a precise generalization, when our TBD tests indicate presence of antibodies, we only have evidence - strictly speaking - that the dog's (adaptive) immune system has had an encounter of some sort with (i.e., been exposed to) the antigens of the organism in question.

It is seriously flawed thinking to rigidly equate low antibody titers with 'only exposure'. Seriously affected dogs sometimes have low titers.

Tom Beckett, DVM 

 

 

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Immune System Stimulators

FWIW: A reminder that it is fallacious to think of the immune system as one monolithic entity that can be turned up or down in toto in a manner comparable to the way adjusting the thermostat in a home heating system regulates the furnace. The immune system is far too complex to fit such a simplistic model.

The mechanism whereby E. canis contributes to the development of "autoimmune" disorders is not simply prolonged "overstimulation" of the immune system. A generally accepted explanation is that some of the proteins with which E. canis "clothes" itself are a near match in composition and structure to proteins that are a normal integral component of the dogs own self in various cells/tissues. After prolonged exposure to these E. canis proteins the immune system sometimes begins to mistakenly identify the quite similar self proteins as foreign and mount attacks against them.

With most all the various purported immune stimulators there are great gaps in knowledge concerning what, if anything, they actually do for good or ill--and this, it seems to me, is a good reason to eschew their use.

Tom Beckett, DVM

 
Read more on the immune system

National Institute of Allergy and Infectious Diseases

 
Wikipedia: another good read.
 
 
 
               Ellie Goldstein's beautiful Borzoi, Seek 
 
 
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