Case 22

Published on 18/02/2015 by admin

Filed under Allergy and Immunology

Last modified 22/04/2025

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CASE 22

Dawn, a 15-year-old African American girl, was debating whether she should go on the spring ski trip that she had planned for so long. She had noticed stiffness in both her hips (and hands) each morning and wondered if that would affect her skiing. However, since the stiffness abated during the day, she thought that she would go, even if it meant only skiing in the afternoons. She enjoyed the trip, particularly since the weather was so warm and sunny, but she was concerned when she noticed a rash on her face. The rash persisted after she returned and so she went to see her family physician, who recognized the rash as being a classic presentation of systemic lupus erythematosus (SLE), and so he referred her to a local rheumatologist.

On questioning, the rheumatologist learned that there was no history of arthritic-type diseases in the family, although a distant cousin had recently been diagnosed with an inflammatory bowel disorder. A urine sample was found to be normal, indicating that glomerulonephritis was not a problem. A complete blood cell count was performed, along with an assay for antinuclear antibodies (ANA). The white blood cell count indicated a mild lymphopenia and neutropenia, reduced red blood cell count, and a severe drop in platelet count (see Appendix for reference values). The ANA antibody titer was significantly high (normal range: 1:40 to 1:120 depending on the laboratory). How would you proceed?

QUESTIONS FOR GROUP DISCUSSION

1. Dawn’s physician recognized the rash across her face as a classic presentation of SLE. What is the underlying cause of this rash? Explain the underlying cause of the arthritis. (Hint: laboratory investigation revealed that Dawn had a high ANA titer.)

2. Dawn has a significant ANA titer. Define antibody titer. Explain why a negative result in this test would rule out SLE but a positive result would not confirm this diagnosis.

3. What follow-up antibody titer tests could you request to further investigate the presumptive diagnosis of SLE? Explain the principles underlying an indirect immunofluorescence antibody (IFA) test.

4. Explain why you would want to measure the levels of complement proteins C3 and C4. Explain what is meant by the expression “Levels of C3 and C4 are concordant with disease activity in patients with SLE.”

5. Dawn’s blood work indicated that she was anemic. Consequently, the physician requested the indirect and the direct Coombs’ tests. Explain the principles underlying these tests and the rationale for requesting these tests in this patient.

6. Dawn’s urine sample was normal, indicating that glomerulonephritis was not a problem. Explain why patients with high antibody titers often present with glomerulonephritis.

7. Explain why UV light exacerbates SLE.

8. Review B cell activation after encounter with antigen. Why would autoimmune B cells never be activated if T cell tolerance is intact?

9. Explain why a biopsy of the lymph nodes in a patient with active SLE would reveal hyperplasia in the cortex.

10. Explain why there are so many different autoantibodies of different specificities produced in SLE.

RECOMMENDED APPROACH

Implications/Analysis of Family History

The absence of a strong genetic link would not negate the presumptive diagnosis of SLE because susceptibility to SLE is multifactorial. The combined effect of hormones, genes, and environment determine disease prevalence, with females having a greater risk of disease, as does being African American. Dawn is an African American female and, as such, is in the highest risk group.

Implications/Analysis of Clinical History

A red butterfly rash on cheeks after sun exposure in a teenage female is a classic presentation of SLE and has been shown to lead to early testing and diagnosis. The rash results from blood leaking out of damaged blood vessels (immune complex–mediated inflammation) into the skin. However, recent studies have shown that when the initial presentation is arthritis (joint inflammation) and/or arthralgia (joint pain), diagnosis is often delayed, despite the fact that these are the most common initial symptoms (60% of patients studied).

Implications/Analysis of Laboratory Tests

Blood Cell Counts

Dawn’s white blood cell count indicated a mild lymphopenia and neutropenia, which is very common in SLE patients and most likely results from autoantibodies to white cells. Low platelet count (thrombocytopenia), also common in SLE patients, can result in bleeding that manifests as bruises and/or rash. Dawn’s red blood cell count was low, indicating anemia, and thus direct and indirect Coombs’ tests were ordered to determine whether the anemia was due to the presence of autoantibodies that target proteins on the red blood cells. (See Additional Laboratory Tests.)

ANA Assay

Dawn had a significant ANA titer. ANA are autoantibodies that are specific for proteins and nucleic acids in the nucleus (e.g., histones, dsDNA, ssDNA). In the ANA assay, a patient’s serum is serially diluted and then layered on nuclear components of human epithelioid cells (HEp-2). If ANA antibodies are present they will bind to the nuclear components of the HEp-2 cells. The presence of ANA antibodies is detected using a fluorescent-labeled immunoglobulin (antihuman) antibody that targets the Fc region of a particular antibody isotype (e.g., Fcγ, Fcμ, or Fcα). This is an indirect immunofluorescence assay (IFA). (Some laboratories may use rat liver or kidney cells instead of HEp-2 cells.)

Antibody titer is defined as the serum dilution beyond which autoantibodies cannot be detected. A positive ANA titer greater than the reference range, in that particular laboratory, is indicative of disease when accompanied by clinical symptoms. Although a negative result rules out a diagnosis of SLE, a positive result is only suggestive because other inflammatory conditions can also have ANA autoantibodies.

Additional Laboratory Tests

A variety of other tests were performed (anti-DNA, antiphospholipid, C3 and C4, direct and indirect Coombs’ test) to examine evidence for abnormalities characteristic of SLE.

Antiphospholipid Antibodies

Antiphospholipid antibodies are a heterogeneous group of autoantibodies that can cause thrombotic events, leading to deep vein thrombosis or strokes.

Anti–Red Blood Cell Antibodies

In patients with anemia, the direct and indirect Coombs’ tests are used to establish whether there is evidence of autoimmune hemolytic anemia, which can occur in SLE when autoantibodies against erythrocytes are present. In Dawn’s case, both the direct and indirect Coombs’ tests were negative (see Case 15), indicating that this was not the cause of the anemia.

Anti-DNA test

To support a positive ANA result, the patient’s serum is screened for anti-dsDNA using an enzyme-linked immunosorbent assay (ELISA) and, if positive, a titer is determined using the IFA technique (see ANA assay earlier). A negative anti-dsDNA antibody test result does not eliminate SLE as a possible diagnosis, because not all SLE patients have anti-DNA antibodies (moderate sensitivity, high specificity test). However, significant titers of both anti-ANA and anti-dsDNA antibodies, as in Dawn’s case, make a diagnosis of SLE very likely.

Complement C3 and C4

Dawn’s serum C3 level was significantly reduced (normal: see Appendix). In general, the serum level of C3 and C4 complement proteins in SLE patients is decreased because immune complexes bind to and activate the classical pathway of complement. Complement activation triggers an enzymatic cascade in which C3 and C4 are cleaved and biologically active fragments are produced. Often the depletion in these proteins is proportional to the severity of the disease (i.e., number of immune complexes). In such cases the level of C3 and C4 is said to be “concordant” with disease activity, and thus can be used to monitor disease and its response to therapy. Successful immunosuppressive therapy is reflected in a rise in the serum level of C3 and C4. Nephelometry of either C3 or C4 (see Case 11) is sufficient to monitor disease in such patients.

DIAGNOSIS

Dawn was diagnosed with systemic lupus erythematosus.

THERAPY

Dawn should obviously avoid sunlight in the future (see later). Topical corticosteroids and hydroxychloroquine (Plaquenil), an antimalarial drug that has a beneficial effect for SLE for unknown reasons, have both been shown to be effective in treating the rash; however, the hydroxychloroquine has also been shown to be effective in controlling the arthritis. Depending on the severity of the arthritis, NSAIDs or mild doses of corticosteroids may be required, and in more severe cases high doses of corticosteroids will be necessary.

Dawn will have to be monitored carefully because immune complex deposition in the glomerulus is the trigger for inflammation and glomerulonephritis (Fig. 22-1). Proteins or red blood cells in the urine would signal this type of inflammation and so Dawn’s immunosuppressive therapy would need to be increased and accompanied by periodic administration of cyclophosphamide intravenously.

FIGURE 22-1 IgG deposited along tubal basement membrane in kidney of patient with SLE. (×100.)

ETIOLOGY: SYSTEMIC LUPUS ERYTHEMATOSUS

Systemic lupus erythematosus is a multisystemic disease involving increased size of lymph nodes as well as the production of several autoantibodies, immune complex formation, and deposition with consequential clinical manifestations. Sunlight (UV light) exacerbates the disease because UV light results in the crosslinking of DNA in cells. The release of DNA in an immunogenic form (UV linked) can lead to autoimmunization. As we shall see later, other autoimmune reactions may have different triggers for tolerance breakdown.

Polyclonal B Cell Activation

It is common in SLE to see evidence for polyclonal B cell activation with increased levels of serum immunoglobulin. Presumably, the increased lymph nodes are reflective of this B cell hyperplasia. Should you be concerned about this (e.g., premalignant or malignant lesions), a biopsy of an easily accessible lymph node could be ordered. Most likely this would reveal follicular hyperplasia in the cortex and increased numbers of plasma cells in the medulla.

There are often a plethora of autoantibodies of different specificities produced in SLE. In part, this is because the antigen(s) implicated in initiation of the disease are complex ones, such as the whole (or part thereof) of a nucleosome or a ribonucleoprotein particle (RNP), which contains several different molecular entities. Patients can produce autoantibodies against each of the different epitopes represented, with each epitope stimulating antibody production by a specific and unique B cell. Following this, in principle, any of these antibodies may form an immune complex with the whole nucleosome (or RNP).

Breakdown in Tolerance

Potentially autoreactive B cells probably exist normally in the circulation of all individuals, but it must be noted that we normally do not activate these B cell clones. Autoimmunity in general, and SLE in particular, represent a breakdown in normal “self tolerance” mechanisms. Exactly why this occurs remains unclear. For SLE, it seems that tolerance breakdown may result from a failure in normal immunoregulatory populations of T cells.

If T cell tolerance is intact, autoimmune B cells are never activated because the appropriate “help” for B cell differentiation to produce autoantibodies does not occur by virtue of T cell–induced regulation. An alternative hypothesis suggests that immune tolerance is broken by virtue of a generalized vigorous inflammation (e.g., UV light exposure). In this scenario, inflammation results in provision of a bystander milieu (of cytokines and other mediators) conducive to polyclonal B cell activation and a resulting differentiation of, at least some, B cells producing autoantibodies. Once these, in turn, produce cellular damage the reaction can become self perpetuating.

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