Q.45 A patient suffering from pneumonia and tuberculosis was found to have very low CD4+
T
cells. In all probability the PRIMARY causative infectious agent belongs to
(A) Klebsiella family
(B) Mycobacterium family
(C) Retrovirus family
(D) Streptococcus family
Low CD4+ T Cells in Pneumonia-Tuberculosis: Primary Causative Agent
Patients with pneumonia and tuberculosis showing very low CD4+ T cells point to an underlying immunodeficiency. The primary causative agent directly destroys these crucial immune cells, worsening opportunistic infections like TB. Retroviruses, particularly HIV, are the main culprits.
Correct Answer
(C) Retrovirus family. HIV (a retrovirus) selectively depletes CD4+ T cells, leading to AIDS and susceptibility to TB and Pneumocystis pneumonia.
Immune Role of CD4+ T Cells
CD4+ T cells (helper T cells) orchestrate immunity against intracellular pathogens like Mycobacterium tuberculosis. Their depletion (<200/μL) causes opportunistic infections: TB reactivates, and pneumonia often stems from Pneumocystis jirovecii.
Disease Context
Tuberculosis alone doesn’t primarily destroy CD4+ cells; it relies on them for control. Low CD4+ counts in TB-pneumonia combo screams HIV co-infection. TB thrives in AIDS patients due to failed granuloma formation.
Option Analysis
| Option | Family | Correctness | Reason |
|---|---|---|---|
| (A) | Klebsiella | Wrong | Gram-negative bacteria causes bacterial pneumonia; doesn’t deplete CD4+ cells. Neutrophil-driven, not T-cell dependent. |
| (B) | Mycobacterium | Wrong | Causes TB but CD4+ cells fight it; depletion worsens TB but TB doesn’t cause primary CD4+ loss . |
| (C) | Retrovirus | Correct | HIV targets CD4+ receptors, causing profound depletion and AIDS-defining illnesses like TB/pneumonia . |
| (D) | Streptococcus | Wrong | Common pneumonia bacterium; extracellular, handled by antibodies/phagocytes, no CD4+ destruction. |
Clinical Insight
In HIV-TB coinfection, CD4+ <200/μL predicts active TB risk. Start ART + anti-TB therapy. Differentiate: bacterial pneumonia (Strep/Klebsiella) responds to antibiotics; PCP needs TMP-SMX.
