@SOC -
IgM stands for immunogloblin class M. It's one of 5 heavy chains that can form the immunoglobulin molecules, which are each made of 2 heavy and 2 light (the heavies are of the same type, and the lights are of the same type, and one b cell makes only immunoglobulins of one heavy chain and one light chain, e.g. IgG-Kappa). That would mean immunoglobulin with heavy chain g (or gamma) and light chain k (or kappa).
So I'm suggesting that you don't have an IgM only problem, but an Ig problem in general (involving IgM, IgG, and IgA to varying degrees). There are many immune derangements. Common Variable ImmunoDeficiency (CVID) comes to mind, although usually the G is more pronounced than the M deficiency - but it's variable... hence the name!
When I say don't pay attention to reference ranges, I mean view them as blurry lines rather than strict cutoffs. So one lab says you are normal on IgG and the other says you are low - neither is right or wrong. The point is that you are on the low end of normal or high end of low, somewhere in that general range. The precise numbers are not important, and vary by lab, time of testing, and many other factors.
It is a bit unusual to see IgM be the lowest, although IgM can be highly variable. This is because most amplification of B-cells starts as IgM, and then the cells undergo a class switch to make either IgG or IgA, which are long term antibodies. (IgD and IgE are treated differently and have different roles.)
I wouldn't follow up on these results if you felt normal probably, but since you don't, I would.
That's not what I meant by lymphocytes. Eosinophils are actually not lymphocytes, they are granulocytes of the myeloid lineage. All blood cells are either from the lymphoid or myeloid lineage, and eosinophils are of the latter. I was more curious about the lymphocyte subset panel (if you have had one) and how the cells are distributed in terms of percentage and absolute numbers (e.g. CD3, CD19, CD8, CD4, CD56) CD3 would mean a T-lymphocyte, which can be broken down to CD4 (helper) and CD8 (suppresor/cytotoxic). CD19 are B-cells. CD56 are NK cells. (Oversimplified a bit but basically correct.) White blood cells (leukocytes) are all the cells that are part of the immune system (not platelets or red blood cells). Lymphocytes are a subset of these, as are granulocytes (eosinophils, basophils, neutrophils). There are others too - macrophages, dendritic cells, etc.
By mild I don't mean you don't have important symptoms, only that severe immunodeficiency leads to rapid death, which you have not experienced.
There's a fair bit of research on ME and Th2 shifts. I don't know that it is usually accompanied by elevated Ig's. However, I've generally not heard of Ig's being depressed at all. Cytotoxic function is usually implicated as defective, which is a Th1 process.
CD8 cells are part of the cellular immune response (they directly kill target cells via perforin/granzyme and other pathways). That they are low suggests a broader immunodeficiency like CVID rather than just IgM deficiency.
A hematologist seems like an appropriate place to follow up on this. He may be able to make some sense of it. It would require more testing.
It may be that ME is rather heterogeneous, encompassing a number of different immune dysregulations, all of which share some final common pathway leading to PEM. Or you may have something else... can't tell from the info we have now. He'll probably start with some blood tests. He might eventually do a bone marrow biopsy, but probably not.
It might be enough justification to get you IVIG, which generally helps ME patients. Dr. Jay Goldstein used it extensively in his early days and it worked well. We don't really know how it works, but it's a general immune suppressant / antiinflammatory and is useful in many autoimmune type diseases, but is also used in cases of immunoglobulin deficiency. You might get it for the latter but it might work because of the former. Most of the time they will not use IVIG in ME patients because it's too expensive and it's in limited supply (it's a blood product - they pool immunoglobulins from other people and separate out the red cells for those who need transfusions). So naturally, it's in short supply - you can't just make more.