Immunology—Helper T lymphocytes (CD4+): In adaptive immunity, helper T cells provide assistance to which cell populations during an immune response?

Introduction / Context:
Helper T cells (CD4+ T lymphocytes) are central coordinators of the adaptive immune response. Rather than directly killing infected cells, they secrete cytokines and provide costimulatory signals that help other lymphocytes and innate cells perform their effector functions effectively. This question tests understanding of which cell types receive assistance from helper T cells.

Given Data / Assumptions:

• Helper T cells express CD4 and recognize antigen peptides presented on MHC class II molecules.
• They secrete cytokines and express costimulatory ligands (for example, CD40L) after activation.
• Target populations for their help include B cells and other T-cell subsets.

Concept / Approach:
Helper T cells differentiate into functional subsets such as Th1, Th2, Th17, Tfh, and Treg. Th1 cells assist cytotoxic T cells (CD8+) and macrophages via cytokines like IL-2 and IFN-gamma. Tfh cells interact with B cells in germinal centers via CD40L–CD40 and cytokines (for example, IL-21) to drive class switching, affinity maturation, and memory formation.

Step-by-Step Solution:

Verification / Alternative check:
Experimental and clinical data show that CD4+ deficiency (for example, untreated HIV infection) impairs antibody class switching and cytotoxic T-cell responses, confirming their dual helper role.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing CD4+ helper functions with CD8+ cytotoxic functions; thinking helper T cells only influence antibody production while ignoring their role in priming cytotoxic responses.

Final Answer:
Certain B lymphocytes and other T lymphocytes.