Which organisms are responsible for infections in primary T cell immunodeficiency, such as thymic hypoplasia (DiGeorge syndrome)?
- • Viruses (e.g., herpes viruses).
- • Intracellular bacteria (e.g., mycobacteria).
- • Fungi (e.g., Candida species).
- • Other ( Pneumocystis jirovecii ).
Primary T-cell immunodeficiency usually manifests during infancy and results in inadequate cell-mediated immunity, leading to infections similar to those encountered in patients with HIV infection, the prototypic acquired T-cell immunodeficiency state. CD4+ helper T cells (Th2 subset) interact with B cells to facilitate immunoglobulin class switching and productive antibody response to most protein antigens. CD4+ T cells (Th1 subset) and CD8+ cytotoxic T cells play a key role in detecting and eradicating intracellular organisms such as viral, fungal, mycobacterial, and Pneumocystis. Treg cells (CD4+ CD25+ FOXP3+ T REG ) are important in peripheral tolerance and absence of these cells leads to early onset autoimmunity. Recently, the Th17 subset of CD4+ T helper cells has been shown to be important in controlling superficial fungal infections. Patients with cellular defects (STAT1/3) or 1L-17 mutations develop severe chronic mucocutaneous candidiasis.
