Topic overview

Start with the big picture

Innate immunity responds rapidly and broadly, beginning with physical and chemical barriers such as skin, mucosal surfaces, acidic conditions, lysozyme, and defensins. Innate cells and pattern-recognition receptors detect threats and help initiate cytokine and complement activity; natural killer cells contribute to defense against infected or abnormal cells. Adaptive immunity develops more slowly and targets specific antigens through humoral B-cell and cell-mediated T-cell responses. Antigen presentation and costimulation support T-cell activation, while clonal expansion generates effector and memory cells. The lesson also introduces antibody classes, primary and secondary responses, helper T-cell subsets, cytotoxic mechanisms, and processes that refine antibody responses.