Mononucleosis and Mononuclear Leukocytes

I think I’ve found the answer to my question but I’d like some confirmation. (One thing this message board has taught me is that a lot of the things I think I know are, um, just not true.)

My daughter has come down with a case of “mono”. While we’re all smart enough to know this is short for “mononucleosis”, our immediate question was “What is a mononucleo?”.

I consulted a couple of reference books and did a web search and learned alot about the disease. The name derives from elevated levels of “mononuclear leukocytes” or “monocytes” in the bloodstream. This is where the tough question comes. Don’t most cells have just one nucleus? Why are these particular cells called out? It seems to me like noticing you’ve seen a lot of birds lately with wings. Normally you don’t call attention to the obvious.

Here’s my guess. I discovered there are other types of leukocytes called, IIRC, “polymorphonuclear” or something like that. While they don’t technically have multiple nuclei, the nucleus is “segmented” (their term). The mononuclear leukocytes have ovoid shaped, non-segmented nuclei. So they aren’t celebrating the discovery of rare, single-nucleus cells. They’re just using a differentiating term for distinguishing one type of leukocyte from another.

So can any of you medical, biological, pathological, histological, microbiological or hematological types out there confirm or correct my diagnosis? It would help if I was right since I already explained it to my family and I’d hate to have to publish a retraction.

I’d say your comments are 100% accurate.

There are two main categories of white blood cells.

Mononuclear cells refer, generically, to white cells of lymphoid/macrophage lineage. And, just as you inferred, “polymorphs” is simply code for the other main type of white cells - the neutrophil (the prototype of the non-lymphoid white blood cell).

Likewise you are right in stating that their morphology-based names are simply reflections of the appearance of their nuclei (a vestige of days gone by when morphology, and not genetic nor other fundamental paradigms, prevailed).

And just if anyone is interested, and so I’ll feel like I actually contribute something to this place, the two types of mononuclear white blood cells are monocytes and lymphocytes. Confusingly enough, it’s the lymphocytes that are increased in most viral infections such as mononucleosis. If it were a bacterial infection, say, then you’d probably see an increase in the pmns (polymorphonuclear leukocytes) otherwise called neutrophils.

Staring at blood smears and counting the numbers of cell types is one of the things I do eight hours a day. Nice to find the information useful outside work. :slight_smile:

The lingo is derived from the concept of “polymorphonuclear” vs. “monomorphonuclear” cells. The polymorphonuclear cells also have one nucleus, but it’s very convoluted and lobulated, hence the name. The nuclei y have many different possible shapes, or polymorphs. The mono cells have one big round-looking nucleus, it always looks about the same, hence monomorph, or shortening even further (and inappropriately, to be technical), mono.

In mononucleosis, for a multiplicity of reasons too dull to go into here, the predominant white blood cell present in the peripheral blood smear is a monomorphonucleated one, as opposed to the usual situation where polys predominate. Hence the name; Mononucleosis.

Qadgop MD

I just wanted to make sure that people noticed this.