13. Macrophages eliminate pathogenic bacteria upon activation by
(a) NK cells (b) Basophils
(c) CD4+ T cells (d) Plasma cells
Macrophages play a crucial role in innate immunity by phagocytosing bacteria, but full activation to eliminate tough pathogens requires helper T cells. The correct answer to this immunology MCQ is (c) CD4+ T cells. This SEO-optimized article breaks down the mechanism and all options for biotech students and researchers.
Correct Answer Explained
CD4+ T cells, particularly TH1 subsets, activate macrophages through IFN-γ cytokine secretion and direct contact via CD40L. This boosts macrophage microbicidal activity, including reactive oxygen species, nitric oxide, and lysosomal enzymes, enabling efficient killing of intracellular bacteria like Mycobacterium tuberculosis. Without this activation, resting macrophages struggle against persistent pathogens, making CD4+ T cells essential in adaptive immunity.
Option Analysis
Understanding why other options fail highlights immune cell roles:
| Option | Cell Type | Role in Immunity | Why Not Correct for Macrophage Activation |
|---|---|---|---|
| (a) NK cells | Natural Killer cells | Innate lymphoid cells that lyse infected or tumor cells via perforin/granzymes and secrete IFN-γ | NK cells indirectly aid by killing infected cells to release bacteria for macrophage uptake, but do not directly activate macrophages against pathogens . |
| (b) Basophils | Granulocytes | Release histamine, IL-4 for allergic responses and parasite defense | Basophils promote TH2 responses and M2 macrophage polarization for wound healing, not antibacterial activation . |
| (c) CD4+ T cells | Helper T cells | Orchestrate adaptive immunity via cytokines | Correct: TH1 CD4+ cells prime macrophages for enhanced phagocytosis and killing . |
| (d) Plasma cells | B cell effectors | Produce antibodies for humoral immunity | Plasma cells target extracellular pathogens via opsonization; no role in macrophage activation . |
This mechanism underscores CD4+ T cell importance in infections like tuberculosis, where their depletion (e.g., in HIV) leads to macrophage failure. For deeper study, explore TH1-macrophage crosstalk in molecular immunology texts.
