A 5-year-old boy with severe, recurrent respiratory infections is undergoing evaluation. Sputum studies reveal intracellular bacteria. Further testing shows that the patient's T cells lack the IL-12 receptor. Supplementation with which of the following substances would most likely improve this patient's condition?

Question

A 5-year-old boy with severe, recurrent respiratory infections is undergoing evaluation.  Sputum studies reveal intracellular bacteria.  Further testing shows that the patient's T cells lack the IL-12 receptor.  Supplementation with which of the following substances would most likely improve this patient's condition?

Quizplus · Accepted Answer

11ec160b_37a0_f79a_9249_5f793fb2bfc4_MD0001_00 Helper T cells that have not yet contacted antigens are called naive (Th0) cells and have T-cell receptors (TCRs) and CD4 proteins on their surface. An antigen-MHC class II complex on an antigen-presenting cell (eg, macrophage, dendritic cell) can activate a naive Th cell by interacting with both TCR and CD4. The activated T cell then differentiates into either a Th1 or Th2 cell. If the antigen is presented by a macrophage, the macrophage will produce IL-12, which stimulates differentiation into Th1 cells. A deficiency of IL-12 receptors on naive T cells prevents differentiation into Th1 cells, which produce interferon-gamma (IFN-γ). IFN-γ is responsible for activation of the macrophage and CD8⁺ cytotoxic response against intracellular organisms, such as mycobacteria. Therefore, individuals with an IL-12 receptor deficiency are susceptible to severe, persistent mycobacterial infections. Administration of IFN-γ improves the immune response to mycobacterium in these patients. (Choices A and B) Both complement and GM-CSF (granulocyte-macrophage colony-stimulating factor) play a part in the immune response against pathogens such as mycobacterium. However, patients with an IL-12 receptor deficiency are unable to produce sufficient IFN-γ and therefore would not be able to mount a sufficient immune response to mycobacterium without IFN-γ supplementation. (Choices C and E) Formation of Th2 cells is induced by IL-4, which also plays a role in B cell differentiation and the production of immunoglobulins. Administration of immunoglobulins or IL-4 would improve the immune response against extracellular bacteria or viruses but would not be effective in stimulating an immune response against intracellular bacteria such as mycobacterium. Educational objective: IL-12 stimulates the differentiation of naive Th0 cells into Th1 cells. Patients with IL-12 receptor deficiency are susceptible to severe mycobacterial infections due to the inability to mount a strong cell-mediated granulomatous immune response; therefore, they require treatment with IFN-γ.

A 5-Year-Old Boy with Severe, Recurrent Respiratory Infections Is Undergoing