What are titers? What do they mean?

[BostonRott]

Since threads on vaccination schedules come up frequently, and invariably the discussion leads to titer results, I thought I'd put something together which tries to explain what titers are and how they work.

A bit of VERY basic immunology. The body reacts to foreign proteins. Each virus or bacteria carries some sort of markers on it's surface that identy it as unique. Think of brands of cars. "Sedans" vs "SUVs" (virus vs bacteria). Sedans are different than SUVs, they are not easily confused with each other and anyone can spot them. Sedans are made by different manufacturers and each one gets its brand (Ford) and model name (Taurus). The brand/model helps differentiate it from other sedans (Honda/Accord). The badge of the manufacturer can be like the virus/bacteria surface marker: something that makes it blatantly obvious.

The body forms antibodies (a protein) against the markers on the surface (not against the ENTIRE virus or bacteria). When the body is first exposed to the foreign protein, it makes a lot of antibodies to fight off this new intruder. Over time, in an effort to conserve energy (it takes energy to make proteins), the amount of antibodies in the blood level decreases. What is left are memory cells, which contain a few surface antibodies against the intruders. If the memory cells bump into what they're looking for, an alert is sent out and the full immune response then happens.

Think of this analogy. The antibodies are the troops, the memory cells are the sentries. It would be a grand waste of any military's power/strength/money to keep the troops running around on full alert ALL the time, looking for a problematic foe. Instead the troops are recalled and a few sentries are left on the look out. Those sentries are the memory cells.

When you run a titer, you are literally diluting over and over. You keep diluting your solution until you can no longer find what you're looking for. In the case of antibodies, this means that you start with blood (containing antibodies) and keep diluting it in solutions until you no longer find any antibodies. The number of times you dilute it gives you a measure of how "strong" the antibody level is.

Think of a glass of water with several drops of food coloring in it, so that it's "cool-aid red." If you want to find out how "strong" the food coloring is, you would take a measured amount of the red water (let's say 1 mL), and add it to a known amount of clear water (9 mL). This adds up to a total of 10mL (1mL red water + 9mL of clear water). This is a 1:10 dilution. Most likely, this 1:10 dilution is still going to be red/pink, but certainly not clear.

You could then go back to your original cool-aid water, and take 1 mL and add it to 99mL of clear water. This would be a 1:100 dilution (for those with knowledge of serial dilutions, you could also take 1mL of 1:10 and put it in 9mL of clear water). If your 1:100 is still colored, then you try again.

1mL of red water into 999mL of clear water (or basically 1 cc into 1 L), gives you a 1:1000 dilution. You would keep following this pattern until finally you end up with clear water. That final dilution, which yields clear water, is known as your dilution strength.

If you have 2 glasses of red water, one with 4 drops of food coloring and 1 with only 1 drop, you would expect to have to do a lot more dilutions of the 4-drop water than the 1-drop water. This is because the 4-drop water is darker/stronger.

So, when you get lab results back on titers, you'll get something like 1:32 or 1:64 or 1:12,800. The second number, on the other side of the colon, (roughly) tells you how many times they had to dilute the sample until they could not find any more. The more you start with, the more dilutions you have to do before you get to zero.

The final piece to this puzzle is the "low titer" result. When using titering to assess a vaccination protocol, you need to draw the blood 2 weeks after the previous vaccine. This way, you can get a measure of the active antibody levels, before they start to drop off and return to just the memory cell/sentries. Titering does NOT measure memory cell capacity, only free antibody.

Therefore, it is ENTIRELY possible to have a very solid immunity in a dog, but if the dog has not recently been vaccinated or otherwise exposed to that antigen (be it parvo, distemper or lyme), there is not going to be a high level of free antibody, and you may get a low titer level.

Hopefully this helps ...... immunology is a very technical field and it's easy to make a muddy mess out of tryin to explain things!

[mwaters]

Whoa Gretchen,

That is FANTASTIC...I never really 'got' titers before...THANK YOU. Very clear.

Cool

[BostonRott]

I'm glad you could understand it!

Dr. Schultz says when running titers, not to worry if they are "low," as long as there IS a titer, then the dog shows sero-conversion (meaning the body recognized the vaccine as a foreign, dangerous, protein).

I personally would booster a dog who only shows 1:2 or 1:4 (assuming they are drawn 2 weeks after exposure/vaccination). If I drew one of my dogs (who previously had GOOD titers when drawn 2 weeks after vaccination) at some random point in time, and the titer was low, I would not bat an eye, and not re-booster. I would simply assume that the dog has had no recent exposure and therefore little or no free-floating antibody.

[MARYDVM]

Another point to remember is that a second form of immunity - called cell-mediated immunity can exist with a titer of 0, and still protect the dog. Killed parvo vaccines produce cell-mediated immunity only. If you were to give your dog a series of killed parvo vaccinations, and then check the titer, you would get a zero until the dog was actually exposed to the live virus - then it would seroconvert and produce a measurable titer.

[SaranBear]

This applies to measuring titres in humans as well? Just wondering if this is the same idea used to measure MMR titres.

[BostonRott]

Yes a titer is a titer.