Exposure of human lymphocytes to bacterial endotoxin (lipopolysaccharide, LPS) typically causes blast transformation in which population?

Introduction / Context:
Mitogens are substances that non-specifically stimulate lymphocyte proliferation. Bacterial endotoxin (LPS) is a classical B-cell mitogen in many species, driving polyclonal B-cell activation and blast formation. Understanding which stimuli activate which lymphocyte subsets is key in immunology labs and diagnostics.

Given Data / Assumptions:

• Mitogen: LPS from Gram-negative bacteria.
• Cellular targets: B cells vs T cells vs monocytes.

Concept / Approach:
LPS engages pattern-recognition receptors (e.g., TLR4-MD2-CD14 complex) and can directly activate B cells (especially in mice) leading to blast transformation and proliferation. T-cell mitogens are different (e.g., phytohemagglutinin, concanavalin A, anti-CD3 antibodies). Monocytes respond to LPS with cytokine secretion rather than classic blast proliferation.

Step-by-Step Solution:

Verification / Alternative check:
In vitro assays show robust B-cell proliferation with LPS; monocytes produce TNF and IL-1 in response but do not show classic lymphoblast proliferation.

Why Other Options Are Wrong:

• T cells: Not directly driven to blasts by LPS.
• Monocytes: Activate and secrete cytokines; not classic mitogen-induced blasts.
• None/Eosinophils: Incorrect; B-cell activation is well documented.

Common Pitfalls:

• Assuming any strong innate stimulus is a T-cell mitogen; specificity matters.

Final Answer:
B cells (polyclonal activation)