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PubMed This is a summary of 5 peer-reviewed journal articles Updated
Clinical Immunology

Understanding Your Lab Results and Diagnosis

At a Glance

Partial IL6ST deficiency is usually diagnosed by matching a disease-causing change in one copy of the IL6ST gene with the person’s clinical findings. IgE, eosinophils, memory B cells, CRP, and specialized cell-response tests can support the diagnosis, but no single result is definitive.

Navigating the laboratory journey for autosomal dominant (AD) partial IL6ST deficiency can be complex because your immune system is “muffled” rather than completely silent. Diagnosis generally centers on identifying a pathogenic genetic variant interpreted alongside your clinical symptoms, sometimes supported by specialized “functional” blood tests [1].

Your Immune Profile: What the Numbers Mean

Your blood work may show a distinct pattern that points toward a Hyper-IgE syndrome (HIES). While not every patient will have all of these findings, common laboratory reports include:

  • High IgE Levels: Many patients with this condition have very high levels of Immunoglobulin E (IgE), an antibody that usually fights parasites but causes allergic symptoms when elevated [1].
  • Eosinophilia: You may have a high count of eosinophils, a type of white blood cell involved in allergic inflammation [1].
  • Low Memory B Cells: Tests often show a reduction in CD27-positive memory B cells. These are cells that help your body remember how to fight specific germs you have encountered before [1].
  • The “Quiet” Alarm (CRP and Fever): Because your IL-6 signaling is impaired, your C-Reactive Protein (CRP) and fever may be lower than expected, even if you are quite sick [1][2]. Always rely on how you feel, your breathing, and your doctor’s clinical assessment rather than just a thermometer or CRP level.

The Genetic Signature and Counseling

Diagnosis is typically anchored by finding a specific type of mutation in one copy of your IL6ST gene.

  • Monoallelic Truncating Variant: This means you have a mutation on only one copy (monoallelic) that acts as a “stop sign,” cutting the protein short (truncating it) [1].
  • Expert Review: A truncating variant is not automatically pathogenic on its own. A clinical geneticist or immunologist must review the specific gene change to confirm it fits the disease profile [1].
  • Genetic Counseling: Because this variant has a 50% chance of being passed to each biological child, consulting a genetic counselor is highly recommended to discuss family testing and reproductive planning.

Why Surface Tests Are Unreliable

You might expect that a genetic defect would mean you have less of the GP130 receptor on your cells. Surprisingly, the opposite is often true. Because the mutated receptors are missing a “recycling motif” (a signal that tells the cell to take them down), they often pile up on the cell surface [1][3]. Simply measuring the amount of GP130 on your cells is not enough for a diagnosis, as levels can be high, low, or normal [2].

Specialized Confirmatory Testing: Functional Assays

To support a difficult diagnosis, specialized laboratories can perform functional assays. Instead of just counting receptors, they watch how the cells respond to a “test signal.”

  1. Stimulation: Scientists take your cells and “ping” them with signals like IL-6 and IL-11 [1].
  2. Phosphorylation: In a healthy cell, these signals cause a protein called STAT3 to “light up” (phosphorylate) to deliver the message [1][4].
  3. Confirming the Defect: In AD-IL6ST deficiency, the cells show a reduced ability to phosphorylate STAT3 in response to IL-6 and IL-11 [1][5].
    (Note: These functional assays are specialized confirmatory tests; they are not available in every laboratory and are not strictly mandatory if the genetics and clinical picture are clear).

Your Completeness Checklist

Ensure the following key data points are in your medical record to help your specialists coordinate your care:

  • [ ] Genetic Test Report: Documenting your specific variant in the IL6ST gene [1].
  • [ ] Quantitative IgE and Eosinophil Count: To track allergic inflammation over time.
  • [ ] B Cell Subset Panel: Looking at CD27+ memory B cells [1].
  • [ ] Vaccine Response Levels: Records of whether you have protective antibodies. Do not skip routine vaccines or seek live vaccines without explicit advice from your immunologist, as safety and timing (especially if receiving immunoglobulin therapy) must be highly individualized [1].
  • [ ] Functional Assay Results: If performed by a specialized center [1].

Common questions in this guide

How is autosomal dominant partial IL6ST deficiency diagnosed?
Diagnosis usually combines a disease-causing variant in one copy of the IL6ST gene with the person’s symptoms and immune findings. A truncating change is not automatically disease-causing, so a clinical immunologist or geneticist must review the specific variant. Specialized cell-response testing can provide additional support when needed.
What do high IgE and eosinophils mean in partial IL6ST deficiency?
High IgE and eosinophilia are common clues and can resemble a hyper-IgE syndrome pattern. IgE is an antibody associated with allergic responses, while eosinophils are white blood cells involved in allergic inflammation. These findings are not present in every patient and do not establish the diagnosis by themselves.
Can an infection cause little fever or a normal CRP with IL6ST deficiency?
Yes. Impaired IL-6 signaling can reduce the usual CRP rise and fever response, even when an infection is significant. Do not rely on temperature or CRP alone; worsening symptoms, breathing changes, and your clinician’s assessment are important.
Why does a GP130 surface test not confirm IL6ST deficiency?
The altered GP130 receptor may build up on the cell surface because it lacks a signal that normally helps the cell remove or recycle it. As a result, GP130 levels may be high, low, or normal, so a surface measurement alone cannot confirm the diagnosis.
What does a STAT3 phosphorylation test show?
This specialized functional test exposes cells to IL-6 or IL-11 and measures whether STAT3 becomes activated. Reduced STAT3 activation can support partial IL6ST deficiency, but the test is not available everywhere and may not be necessary when the genetic and clinical evidence is clear.
What results should be included in my IL6ST deficiency medical record?
Keep the genetic report with the exact IL6ST variant, IgE and eosinophil results, the B-cell subset panel including CD27-positive memory B cells, vaccine antibody responses, and any functional assay results. Ask your immunologist before changing routine vaccines or receiving a live vaccine, especially if you receive immunoglobulin therapy.
Can partial IL6ST deficiency be passed to my children?
Because this condition is autosomal dominant, a person with the disease-associated variant has a 50% chance of passing it to each biological child. A genetic counselor can discuss family testing and reproductive planning.

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References

References (5)
  1. 1

    Dominant-negative mutations in human IL6ST underlie hyper-IgE syndrome.

    Béziat V, Tavernier SJ, Chen YH, et al.

    The Journal of experimental medicine 2020; (217(6)) doi:10.1084/jem.20191804.

    PMID: 32207811
  2. 2

    New Dominant-Negative IL6ST Variants Expand the Immunological and Clinical Spectrum of GP130-Dependent Hyper-IgE Syndrome.

    Arlabosse T, Materna M, Riccio O, et al.

    Journal of clinical immunology 2023; (43(7)):1566-1580 doi:10.1007/s10875-023-01517-4.

    PMID: 37273120
  3. 3

    Fine mapping of heterozygous IL6ST nonsense variants underlying autosomal dominant hyper-IgE syndrome.

    Ashihara K, Asano T, Takeuchi K, et al.

    JCI insight 2025; (10(14)).

    PMID: 40526438
  4. 4

    Selective loss of function variants in IL6ST cause Hyper-IgE syndrome with distinct impairments of T-cell phenotype and function.

    Shahin T, Aschenbrenner D, Cagdas D, et al.

    Haematologica 2019; (104(3)):609-621 doi:10.3324/haematol.2018.194233.

    PMID: 30309848
  5. 5

    The Human GP130 Cytokine Receptor and Its Expression-an Atlas and Functional Taxonomy of Genetic Variants.

    Chen YH, van Zon S, Adams A, et al.

    Journal of clinical immunology 2023; (44(1)):30 doi:10.1007/s10875-023-01603-7.

    PMID: 38133879

This page is for informational purposes only and does not constitute medical advice. Your immunologist and clinical geneticist should interpret your IL6ST results and guide decisions about testing, vaccines, and infection monitoring.

Guide contents Autosomal dominant combined immunodeficiency due to partial IL6ST deficiency
Research & Literature
03 The Biology of Your Diagnosis 05 Standard of Care Treatment and Daily Management