6

CASE 6

Jason, a 6-year-old boy who lives on a farm, has convinced his parents that he should be allowed to take care of the chicks that are in the hay loft area of the barn. He is intrigued with this brood of chicks and spends hours just lying down in the hay to watch them or dragging hay over to their nest. When he is not in the barn, Jason is “helping” his mother with the new garden. After several weeks of this regimen, Jason started having difficulty breathing and seemed to “always be coughing.” The parents took him to their family physician, who had already treated Jason for a severe diaper rash (Candida albicans) when he was an infant and over the past few years for numerous severe bacterial infections.

The physician ordered several tests, including a complete blood cell count and differential, total serum immunoglobulins, immunization antigen titer, T cell function test, and a bronchoalveolar lavage to use for culture. The white blood cell count showed a mild leukocytosis, but the differential indicated a normal percentage of each cell type. Total IgG was normal for the pediatric population (see Appendix), as was the antibody titer to immunization antigens. T cell function was normal. An inquiry into Jason’s family revealed that he had three older sisters and two brothers, none of whom had presented with clinical symptoms analogous to those for which Jason’s parents had sought medical attention. How would you proceed?

QUESTIONS FOR GROUP DISCUSSION

1. Fungal infections (e.g., Candida albicans) occur frequently in patients with T cell disorders. However, laboratory tests indicated that this patient’s T cell number and function were normal. What other cell type plays an important role in the elimination of fungal infections?

2. This patient has a history of both fungal and bacterial infections. Therefore, which cell type should you consider investigating with respect to cell number and function?

3. The phagocyte plays an important role in the innate immune system using as its armamentarium lysosomal enzymes, reactive oxygen intermediates (ROIs), and nitric oxide. ROIs are generated during the respiratory burst. Which enzyme complex is required to trigger the sequence of events that generates the ROIs?

4. Describe the laboratory tests used to determine if the NADPH oxidase enzymatic complex is functional.

5. Culture of the bronchoalveolar lavage fluid revealed that Jason was infected with Aspergillus fumigatus, a fungus that is widely distributed in nature, including garden soil and hay lofts. Despite this, aspergillosis is not common. Explain.

6. In a normally functioning immune system, T cells enhance the phagocytic ability of phagocytes. Explain.

7. Recently, prophylactic administration of the cytokine interferon gamma (IFNg) has gained popularity as a therapeutic intervention to treat patients with a defect in a component of the NADPH oxidase complex. Explain. What is the source of IFNγ in an intact immune system?

8. Describe some of the effects of IFNγ, other than effects described in question 7.

9. Describe the rationale for bone marrow transplantation and gene therapy.

10. Explain the role of NRAMP-1 in host defense.

RECOMMENDED APPROACH

Implications/Analysis of Family History

An inquiry into Jason’s family revealed that he had three older sisters and two brothers, none of whom had presented with clinical symptoms analogous to those for which Jason’s parents had sought medical attention.

Implications/Analysis of Clinical History

Whereas bacterial infections can be commonly seen in complement and cell-trafficking abnormalities, susceptibility to fungal infections should trigger a concern to investigate a defect in phagocyte or T cell function.

Tags: Problem-Based Immunology

Jun 18, 2016 | Posted by admin in IMMUNOLOGY | Comments Off

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