What do Toll-like receptors do?

• A. Use pattern recognition in the membranes of host cells to stimulate different innate immune responses.
• B. Present antigens to T cells.
• C. Activate B cells directly.
• D. Secrete antibodies.

Answer: (A)

Toll-like receptors are pattern recognition receptors on host cell membranes and in endosomes that detect conserved microbial components. When a TLR recognizes a pathogen-associated pattern, it triggers signaling pathways that stimulate innate immune defenses, including inflammatory cytokine production, type I interferons, and upregulation of costimulatory molecules to enhance antigen presentation. This initial alarm not only helps recruit and activate other innate immune cells but also helps shape the later adaptive response by maturing antigen-presenting cells for T cell activation. They do not directly present antigens to T cells—that role belongs to MHC-peptide complexes on antigen-presenting cells. They also do not activate B cells directly nor secrete antibodies, since antibody production comes from B cells after receiving help from T cells and plasma cell differentiation.